UK Cherub - tech

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

2007 Nationals Entries

The following have confirmed that they are coming:

No	Sail Number	Name	Comment
1	2694	Badger's Nadgers	Picking up new mast on friday morning, sailing friday afternoon!
2	2692	Natural Born Skiffeurs	French contender
3	2688	Atum Bom	You bet
4	2686	Primal Scream	Hope to avoid the rocks this year.
5	2652	The Flying Trifle	Last place is a happy place!
6	2648	Comfortably Numb	Extra sticky paint may lead to early planing (or multi coloured crew)
7	2643	Taking Liberties	Tinner's going DOWN!
8	2642	Little Fluffy Clouds	Eek, it's July already! First time out at the nationals then
9	2603	Aggro	For the weekend.
10	1494	Huckle (The Maori Hunter)	For the weekend.
11	2638	Prodigal Son	For Sat Sun and Monday when I find a lightweight crew to compensate for the lardy helm
12	2657	Slippery When Wet	Just got to learn how to sail the boat!
13	2673	Dangerous Beans	Ready to fly…
14	2693	Subtle Knife	Will be there with Hoppy helming expect to see some very hungover sailing
15	2645	Cheese Before Bedtime	Boat at WPSNA, Now totally psyched out after trying to keep up with A'Bom & Shiny on Sunday
16	2649	Dangerous Strawberry	Got a crew and ready to represent the bistros!
17	2698	Ronin	Flying high
18	2685	Loco Perro	Big, white and out of control
19	2644	Suicide Blonde	Yellow and speedy
20	2651	Suicide Blonde	Slightly strange and in no way brown
21	2683	Pocket Rocket	Is that a rocket in your pocket or are you pleased to see me?
22	2669	Catananche	Flying the Weston flag
23	2680	Nautilus Pompilius	Mostly pretending to be a 12 foot skiff!
24	2655	Monkey Magic	Bananas clearly ARE the only fruit
25	691	Suspense	Long live the symmetric boats
26	2656	Therapy	White and very cool

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

These are some construction shots of my Italian Bistro, which was completed from a professionally build vacuum bagged shell and false floor. The shell was made in a female mould flopped off Norwegian Blue (Dave Roe's Italian Bistro). Wiz has now moved on, but was then one of the top high tech boatbuilders, having been involved in several major projects, inclusing Tony Bullimore's “Spirit of Apricot” and the first of the Nigal Irens ILAN motor trimarans, which took the round Britain powerboat record.

The shell is biaxial glass over foam with local carbon reinforcement, the foredeck 3mm Marine ply and the side decks 4mm. Dick Jarrett, who'd been building high quality wood Cherubs a few years previously, has some good quality marine ply stored away, which I gratefully purchased. These days such materials are prohibitively expensive…

Collecting the shell from Wiz Deas (then) yard at Pill near Bristol. Amongst other well known projects the wing mast for “Spirit of Apricot” was built there.

The shell as collected. Its biaxial glass over Termanto foam. I've never quite understood why Wiz put the carbon in the floor, but its certainly stood up to all sorts of abuse over the years.

Decking the boat in the front room. Note that there is no deck level beam from the prodder to the bow. This was a mistake - the boat bent slightly under rig loads.

Although the shell is foam sandwich I decked the boat in wood, as I didn't yet feel comfortable with foam. Thus we have a typical wood boat decking arrangement, with stringers and little ply bulkheads to support the decks. Alistair Cope helped - well pretty much built - the tank sides, which were my first experience of foam sandwich.

Completed boat fresh out of the front room in 1990. The two tone paint job was sprayed by Wiz. The front room as a building workshop is fairly normal for Cherubs, but was rather frowned upon by my Landlords when they found out!

Fairly minimalist internal layout. The ports visible in the sidetanks forward are for the spinnaker sheets, which run through the topsides to vertically mounted cam cleats just inside the deck. The spinnaker chute comes back into the port sidetank.

And a view from the upstairs window. I suppose its worth noting that the boat is complete and fully fitted out in these pictures, and also that the boat predates asymmetric spinnakers and bowsprits. Since the initial bowsprit conversion it no longer has a sealed bowtank and spinnaker chute, and doesn't look so tidy either.

Pictures 1 & 2, © Alison Wilde, remaining © Jim Champ.

Oh yes, spinnaker chutes. Commercially available ones were too large and too heavy. I decided to make my own. Big mistake - it was more trouble than any other five components of the boat put together. If you're ever tempted to build a spinnaker chute take my advice and don't.

The other thing I wouldn't do again is deck the boat in wood. Foam sandwich is (much to my surprise) so much easier to work with. The passing of time has seen the boat change, like all Cherubs. It's recently acquired a snout.in a second significant modification.

This page is dedicated to the memory of my friend Steve Dyer (1956-1999). If he hadn't inspired me to get off my backside and make a major career change - or even start - I would never have been in a financial or domestic position to build the boat at all.

Jim Champ

Adding a snout to an Italian Bistro

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Adding a snout to an Italian Bistro

Mid life surgery is not uncommon on Cherubs. Here my 10 year old Italian Bistro is gaining a snout in 2000. Its all hand laid up glass over foam with local carbon reinforcement except as noted.

Ready to start - angle grinder waiting!

The idea behind the odd bracket was so that the pole could retract into the side tank rather than into the crew area. The boat was built without a bowsprit, and there was no room for one under the daggerboard case support.

Clouds of glass dust later (always wear dust mask and other protection) all the old arrangement is gone.

At this stage I chopped a hole in the stem to work out the correct position for the pole. Its easier to work these things out with a good reference point.

The new snout, with gunwale arrangements etc still to come. I made up flat panels off the boat and then located and glued them together in position.

Bulkhead which supports the bowsprit.This one is critical and needs to be strong!

There's still the hole from the old bracket to fill, plus the gunwale arrangements to create.

Close up showing unidirectional carbon reinforcement. All the rig loads come into the snout.If this falls off it will be disastrous!

Spinnaker chute area. The “chute is made from expanded polystyrene, covered in a glass/kevlar laminate, kevlar being less prone to being cut through.I'm not sure I've got a big enough spinnaker chute after getting all the beams in the right places for maximum strength.

Ready to deck. The two diagonal beams to the end of the chute are carbon over balsa, intended to reduce the tendency of the boat to bend under rig load.

The “chute” contains a carbon transverse beam to triangulate the loads from the new diagonal beams. You can now see the strip wood gunwale which the ply deck will glue onto. As the rest of the gunwales are wood it seemed more elegant to continue the wood to the bow.

Ply deck glued down and ready to trim. The deck is in two pieces, joined asymmetrically to port. Were I doing a more major conversion I'd take all the wood decks off and replace them with foam, removing all the wood strip etc. I wasn't used to foam sandwich back in 1989 when I finished the boat from a pro built shell.

And here's the completed project, with brand new jib.

All photos © Jim Champ

Anti Bruise Technology

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Anti Bruise Technology

After a particularly poor showing at the Draycote blast, Team Trim have decided to finally get around to a job that has been needed since we bought Ooops. Namely to remove the now obsolete castle, the knee eating ridges in the floor and to add kick bars and pro-grip to the interior. The following describes the progress:

Decide not to sail again until boat does not destroy knees – 25th March 2007
Buy a garage – 28th March
Buy pro grip – 29th March
Make garage fit boat – 31st March
Remove interior – 2nd April
Reinforce back of centreboard mound - 7th April
Apply pro-grip - 8th April
Touch up interior paint - 9th April
Go Sailing - 14th April

Additional items left:

Make spinni single line - 14th April
Reinforcement of wear points wih Polymorph
Add kite sock

1) Decide not to sail again until boat does not destroy knees

This is a vital step. The real thing driving this project is the memory of Hayley struggling to get up the stairs to the bar at Draycote. Given that there was a warm shower, a cup of tea and a beer waiting at the top Mrs Trim would normally have been up the stairs before I could blink; I ended up offering to carry her¹⁾.

Others who sailed the boat that weekend (Noicey and Stu) also suffered knee bruises and claimed to have no grip.

Notes: (1) Angled grip patches on deck provide no grip and destroy knees unlucky enough to hit them (2) Castle is no-longer of use and gets in the way. It also hurts when you hit it on the way down the capsized boat.

2) Buy a garage

We live in a two bedroom second floor flat at the North end of Brick lane. We are lucky to have a gated parking space, but the resident’s committee complained to the landlord when we parked Maud (a landrover) with Ooops on the roof.

A more subtle approach is needed, so we bought the Garage – an LDV Convoy.

3) Buy Pro-grip

Ordered sheets of 2mm lunasoft SL ²⁾ (used for innersoles) and a “bund” of 25mm thick stuff³⁾ for “kick bars” from www.algeos.com. I’ll have some of the latter spare after this so feel free to get in touch.

Total package weighed 4.5kg on delivery, so might have to re-think how much I was planning to use.

4) Make garage fit the boat

One of the front seats needed to go to allow the bow to protrude into the passenger area. As I needed the drivers seat and the passenger seat was a twin a small internal modifaction was required. This was subtly effected using a grinder and a Stanley knife. Some duck-tape was then used to make the remaining seat look presentable. I’ll buy some seat covers next weekend incase my handiwork offends any traffic police.

5) Remove interior

Luckily the Garage came with a 3kW inverter that is driven directly off the engine. So I parked up away form the flat and applied the grinder to the inside of Ooops! Most of the rear patches were rotten on top and the castle almost finished off my grinder blade. I then got busy with the band sander and left a smooth-ish interior.

NOTE: Always use gloves and a face mask. Grinder Vs Boat results in lots of dust. In addition try not to park near to any clean looking cars as the dust from your handiwork will travel downwind.

6) Reinforce back of castle

A piece of the old castle was used to provide sway stiffness to the rear of the remaining centre board case tunnel. This will also provide the anchorage for the bow-sprit retrievalelastic and tack line. The plate was cut at an angle to allow a resin equivelent of a “full penetration butt weld”. Two patches of bi clost were then added add shear capacity/stiffness. The lower edge also has a fillet of resin behind it to increase bond with deck.

7) Apply pro grip

Newspaper templates were used to cut the pro grip. This was then attached using Evostick Impact adhesive. This is a one-hit solution and takes real care to get the first contact correct. Luckily the progrip is failry strecty and forgiving to apply.

8) Touch up interior paint

Hayley decided that after all this work it would be nice to make it look the part….

9) Sail boat

Took Oops! out in light breeze on Saturday 14th. Normally this would be a painfull experience for both knees. However the new interior works a treat and was almost comfortable. Spinni works better and the single line deployment is an absolute must. For anyone who still has two lines I can only advise that it will take about five minutes of thought to convert your system!

¹⁾

she declined

²⁾

Product code OG1405

³⁾

Product code OG2432

Snouting

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Snouting

This page logs the addition of a snout to Oops. It is no fun owning a boat that is not sailable, so the plan is to have it back in the water for Bank Holiday Saturday (25th August). This corresponds to Day 15!

Day 1, Hit 1

Cook dinner for 6 and sit around discussing ways to do the job. Desert of apple pie followed by penning cut lines onto hull.

Day 2, Hit 2

Cut/grind hull. Make cardboard templates. Laminate one side of a piece of foam with weave.

Day 3, Hit 3

Cut sides from foam, and attach to hull using flaps

Day 4, Hit 4

Sand sides, add weave to bottom Attach rear bulkhead

Day 5, Hit 5

Attach front bulkhead and add weave to secure rear bulkhead

Day 7, Hit 6

Top of snout goes on, sand bag ensures everything touches.

Day 8, Hit 7

Sand, sand and more sanding. Add some filler.

Day 9, Hit 7

Outer weave in place and lots of Uni to hold on the front shackle. Unfortunately it was a hot day and the resin started to go sticky before we were finished. Application of balloon and surfboard required to get things to roughly sit where we wanted. This is a bit worrying as if this goes wrong the mast will fall down!

Day 10, Hit -

Laurence visits my parents house and bursts the balloon!

Day 11, Hit -

Wedding anniversary.

Day 12, Hit 8

Do you like bubbles dad? This used to be the most annoying ad on tele, but learn a valuable lesson last night;

DO NOT LAMINATE AGAINST GRAVITY WITHOUT A VACUUM PUMP

Sides of weave were bubled out where it had sagged off whilst drying. Turned boat upside down, cut out weave bubbles, sanded the remaining edges down and re-laminated the sides. Also added a top stringer to the inside of the foredeck and stuck on a non structural extension to the spinni pole.

Not bad for a night both Hayley and I were in work at 8pm (and the garage is 30 minutes from our flat!).

Day 13, Hit 9

Strange rituals outside a semi in suburbia.

No superstition. Just a visit from the good doctors. We left it to Will to beef on his typical rig loading. Last time we let Will tension our rig he broke the front spinni pole bulkhead with the boat breaker, so the hope is that this initial proof load is a good sign. Our aim of sailing on Saturday is almost in reach…

Day 14, Hit 10

Now that we know we are on the right path it's time to tidy up. Hit 10 was simply sanding. Lots of Sanding. Hayley looked like a chimney sweep by the time we left! Bow now also has been blended into the colour scheme.

Bogged a fitting on using a backing plate and sanded down the centreboard.

Day 15, Hit 11

BOAT FINISHED AND READY TO SAIL!!!

(only snag being no wind at BBSC). Got the boat wet on Sunday, pictures to follow. Roll on Carnac…..

Velocipide 2675 Build

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Velocipide 2675 Build

Building 2676 Shiny Beast

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Building 2676 Shiny Beast

AquaMarina Build Photos

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

AquaMarina Build Photos

AquaMarina was made from a hull shell supplied by Bloodaxeboats and finished by Phil Alderson in Aberdeen

Bow area with false floor in place and spiniker pole lying on top.

Kingt Post, bulkheaads and centerboard case

Looking aft at the corner peices that support the top of the side decks

Looking forward with the false floor in place.

Another forward view showing the king post.

Looking down on the king post.

The workshop, this picture does not show the I14 sail that hung above the boat stopping the dirt from falling from the roof down onto the boat.

Another view aft

Looking at the transom before the gantry went on.

Close up of the one of the tubes that will make up the racks

Rack Tubes agian

Nearing completion, faired and ready for painting. The longtitudinal tubes were left off till the end to give more space in the workshop as it had now changed to a small garrage.

Rigging up for the first time at the side of a road in weymouth

The original Gantry was too close to the water and the sticky out gudgions were failure prone. So it was cut off and replaced.

Much neater.

Ignore this (delete me on or after 3/7/2006)

Building a Single Skin Rotating Gantry

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Building a Single Skin Rotating Gantry

The gantry on Pocket Rocket needed modification to allow for the use of a T-foil, the shape of the existing one made this difficult, I was unsure about its strength and stiffness as it was made from foam struts with a curve along their length. So I decided to build a new gantry.

The methods I used to build the gantry are outlined below, they may or may not work for you, involve the use of dangerous chemicals and failure while sailing renders your boat uncontrollable, if you intend copying any of the techniques used please ensure that you understand all the risks involved.

The Shape

The Gantry is to be hinged on the back of the boat near to the corners of the transom for strength, it can be thought of as being made from two isosceles triangles with the tips at the transom and the short edges meeting where the rudder pin is to go. To give it strength in compression the edges of the triangles were to be folded over to make flanges which would also serve as a location for the rudder pin. As most of the strength and stiffness of the gantry is in the triangular shape and the flanges, the stiffness of the flat panels between the flanges is not critical to the overall stiffness of the gantry so single skin construction can be used, which should save some weight compared to using foam sandwich.

An important part of the design of the gantry is the hinged attachment to the back of the boat, this must be strong and stiff enough to take not only the steering, drag and lifting loads but also to prevent the spreading of the gantry under these loads.

Building the Mould

The mould was built from various off cuts of MDF and it was shaped so that the moulding would slip off at the end and so that the bottom of the gantry was at 90 degrees to the rudder pin so that the bottom of the gantry and the rudder stock were roughly parallel, this avoids creating a cam that acts to self center the rudder when the T-foil is lifting. The sections of MDF were glued and screwed together and the corners of the mould were rounded off with a router and sand paper to avoid any sharp corners, making lamination easier and giving the finished gantry a better look. The mould was then saturated with polyester resin and covered in a light glass cloth, this would help to seal the mould and allow a vacuum bag to be used when laminating the final piece. Polyester resin was used as it is cheap and would cure quickly, for a single use mould like this using Epoxy would be overkill. The mould was faired with car body filler, and then painted, and sanded through the grades to 400 grit wet and dry. Car body filler was again used as it allowed a quick fill, sand cycle and was cheap. With the mould complete it was coated in several layers of realise wax ready for use.

Building the Gantry

The shape of the gantry would provide much of the strength and most of the load would be through the edges and through the flanges so the laminate spec was devised to use unidirectional tape in the flanges with woven cloth to provide some toughness to the flanges and stop them from cracking along their length.

To spread the load and to create the bearing surface for the hinge I made up two glass tubes on the same diameter rod as was to be used for the hinge, these were then held in alignment with a long rod and attached to the mould before laminating the remainder. If I were to build the gantry again I would probably do this slightly differently as these pieces were awkward to hold in place, and added an extra two laminating steps to the construction.

From the inside of the mould the laminate spec is:

200gsm +- 45 tight woven 50mm cloth tape along the centreline and extending up to the flanges
300gsm Uni along full length flange
300gsm +- 45 woven carbon over the whole gantry
300gsm Uni short sections along flange, around hinge
300gsm Uni along full length of flange
200gsm 2×2 twill 6 small tapered layers around the rudder pin bearing point on the flanges
200gsm 0-90 2×2 twill over the whole gantry

This was then covered with peel ply, bleed film, breather cloth and finally the vac bag, the vacuum pulled and allowed to cure. For more details on the vacuum bagging process please read the Vacuum Bagging article.

Once cured the Gantry was removed from the mould, some extra reinforcement was added around the hinges on the internal part of the gantry. Finally it was given a clean to get rid of traces of realise wax, lightly sanded and given a few coats of varnish to protect it from the UV, and mounted on the boat.

The new gantry including the hinge pins weighs 680g plus approx 100g added to the boat for the hinge points and the hard point, this can be compared with the removed parts of the old gantry weighing 1250g. Some of this weight reduction will be lost in the purchase system for the T-foil but it will still be lighter than adding a T-foil adjustment system to the existing gantry.

Pictures

Lessons Learned

Use Bigger mould Flanges – the flanges on the mould did not extend far enough past where I wanted to laminate, making it difficult to ensure that no fibres, peel-ply, release film, bleeder cloth or epoxy went over the tacky tape creating leaks.
Hinge simplification – I would attach the hinge bushes internally after laminating the gantry to reduce the number of steps in the lamination, the downside of this is that the alignment of the mould would be more critical.
Use more release agent - the laminate stuck to the mould in a couple of spots, making it difficult to release and damaging the mould.

The build of 2684

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

The build of 2684

2684 The first US Cherub

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

2684 The first US Cherub

Skip Kovacs building the jig for the first US based Cherub.

For more of the build of the boat see The build of 2684

Exultant Jubilation - The Build

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Exultant Jubilation - The Build

The chronology of the build will appear here when I get the photos.

The end of the build Sept 2009

A Little less conversation...

...A little more action

With the door to the Room of Requirement now officially sealed⁴⁾, we have moved the boat and all of the rest of our junk to my parents garage in Sidcup.

Living in Holland is cramping progress a little, but at least the long lonely evenings without Hayley have been put to good use. A public thanks to Dave G. and Rob L. for not minding me turning our sitting room into a sail loft.

Many thanks to Allen (and Harbour Wall) for the fitting package. We hope to get everything wet as soon as we can…

What went into the boat - Cookbook

The following is a description of the layups used in various parts of the boat.

Hull

Skin

The outer skin is made from a carbon sandwich. 200gpsm carbon weave vac'ed onto a male mold. 8mm thk 80gpsm (gram/m^2) foam stuck down to that and then 200g/m^2 carbon weave vac'ed onto the outside. The bottom panel has a second layer of 200gpsm from the stern to about a foot past the mast foot (resulting in a thicker laminate for some stone protection).

Butter. Both sides of the foam was buttered. Butter was used to stick the foam to the cured carbon, but on the outer surface it was allowed to dry and then the hull faired before the outer carbon was added. Butter reciepe used - 260ml of resin mixed to a tub of bubbles (tub previously contained M&S chocolate bites). Butter spread using a window squeegy.

Deck

As per the hull. Extra glass layer added where the crew are likely to stomp.

Bulkheads

Made with a simialr sandwich to the hull (200gpsm carbon weave, 80kg foam) laminate on each side was not parallel(but did not achieve 45 degrees). Additional unis run diagonally accross the main bulkhead and under the amst stump to ensure the load is distributed.

Mast Bottom Section

Mandrel

Made Mandrel on an (~52mm) OD plastic tube mandrel. Prepped with a good layer of silicon spray and then lamintated ontop of.

Hit 1

1 layer 200g weave, wound helically in 150mm (6“) strips to give +/- 45 fibres (10mm overlap between helix rounds). Consolidate well or “strangle”. 4 layers 300g uni - as 0 degrees as possible. Consolidate well or “strangle”. 1 layer 100mm wide peel ply applied in 50% overlapping helix in the same direction as base layer. Really beast this on. Some breather and vac down with a very thin bag - this results in few wrinkles and no “pinches”. Establish the vaccume using only the surface of the plastic pipe, so it does not encompass the ends as otherwise the bag gets sucked in and bursts. Lay pipe on the floor whilst curing and line up the floppy item with something straight (a couple of bits of 4×2 works a treat).

Bake - for this we used a tea urn, some plastic tubing and a central heating pump to circulate the water.

Hit 2

Be brave - leave it on the mandrel, but rotate the mandrel inside the mast first to ensure it has not got stuck. Sand off the helical leftovers form the peel ply and then add a layer of 0-90 weave. Peel ply, vac and bake as Hit 1.

Mast tip

Mandrel 1

2m tip, Mandrel tapers uniformly. 24mm OD at tip, 50mm OD at 2m from tip. This needs to be machined down once made to allow joint at 52mm ID of mast bottom section.

Madrel made by hammering some 10mm thread (with nuts on) into a 25mmOD scffold bar. This “tapered bit of metal” was then coated in wood, by routing a channel into some 2×4 and gluing the wood/metal/wood sandwich togehter. The resulting 4” square wooden object with a metal centre is then ready to shape.

The next bit is fun. Make a parrallel jig big enough to fit your object into (i.e. 4“ wide), check your power plane can sit ontop of both sides at the same time withouht cutting into the jig. Support the ends so the centre of the wooden sandwhich can rotated at the correct height off the sides of the jig at each end (i.e. centre of one end is the fat radius down, the other end is offset the thin radius down). Use a power plane to cut until you hit the the jig sides, rotate, plane, rotate, plane, rotate. This creates more shavings than you could ever believe, but results in a round uniform tapered object.

Nearer the tip you may need to strip out the outer wood to reveal the scaffold bar and then support the bar here. This extra bit can easily be filled and faired after the rest is shaped. Ensure the taper is selected so you do not need to plane through the scaffold bar!

Once shaped, sand until the thing looks like a snooker cue. To finish the mandrel heat a number of “tealight” or similar candles and use a small roller to apply wax to your sanded “wooden” mandrel. Keeping the wax hot ensures you can roll out any bubbles in the wax (we found this easier than ironing the wax).

Hit 1

1 layer +/-45 200g. Applied as a helix as before. Cut tapered uni cloth for the tip. Apply 4 layers of 300g uni, start at 12,3,6 and 9 o'clock around the madrel to ensure there is a good distribution of o fibres around the taper. Peel ply, vac and bake as lower mast

Hit 2

Weave. (200g at 0-90) After baking remove the vac bag,peel ply and anthing holding the carbon onto the mandrel. Tie around the carbon to hang it from the ceiling and then bake some more. Mandrel falls out of bottom

Hit 3

Measure ID of mast bottom section. Run some tape around a suitably sized hole saw and then ram it down the fat part of the tapered top section. Rotate on a power drill and use a sanding paddle (or random orbital) to create a flat uniformed OD section to socket into the mast base. Wear a mask, gloves and full body protection for this step - there is a lot of carbon dust. Join mast tip and bottom section with the epoxy of choice (I used my standard epoxy with fibres, others swear by spar bond).

Mandrel 2

This is a revised tip section to give a stiffer mast for use with our sail-plan. Mandrel 1 was too floppy at the tip - worked well with a Fyfe cut sail though! If you are making a mast for a Mandrel 2 tip we would recommend adding an additional layer of 300gpsm UD between the two spreader sets. This results in a mast that appears compatible with the standard Hyde sails (Daemon, GT60 or Ronin cut) - please contact the author before bothering Hyde!

1.8m tip section. Made by adding a timber sandwich around a 25mm OD scaffold bar (these are thin bars used for handrails). Mandrel was machined by rotating under gravity - resulting in a 25mm OD mandrel at tip and 50mmOD mandrel at 1.8m from tip. Mandrel taper is not linear - more gherkin shaped. From 2.8m onwards mandrel did not taper, to make fitting possible without lots of sanding.

Spreaders

From mast tip

Item	Mast 1	Mast 2
Tip	2m	1.9m
Goose neck	5.7m	5.7m
Length of top spreader (from mast face)	40cm	40cm
Sweep backwards (from mast face)	19cm	19cm
Length of bottom spreader (from mast face)	40cm	45cm
Sweep backwards -bottom (from mast face)	19cm	16cm

Middle spreaders at 1/2 way between Goose and First spreaders. The Mast 1 figures are before the addition of the “boots”, these were added and resulted in the Mast 2 dimensions

Spreaders made by shaping some random offcuts of foam. Would suggest they are bigger than you think necessary <attach picture> we broke a few on Born Slippy's mast so a went overboard on Exultant's. Layup is 6 layers of 200, some 300, some weave and some other offcuts.

When attaching spreaders we sat the tube on the floor and positioned cardboard boxes at the spreader position. After careful measurement and drawing on the boxes, the spreaders were then hot glue gunned onto the boxes. The individual spreaders were then bogged in place. Once set, a couple of layers of weave were then vac-ed over the join to make the joint even stronger.

Racks

Built on mast lower mandrel mast lower but with 3 layers of 200g uni (plus 2 layers of 200g weave, one helical at +/- 45 and the other at 0-90)

Mast stump

Built on mast lower mandrel but with 8 layers of 200g uni (got scarred and bored whilst laminating)plus helical and 0-90 weave. .

Rack supports front

Built on mast lower mandrel but with 6 layers of 200g uni, plus helical and 0-90 weave. .

Rack supports rear

Built smaller diameter plastic pipe 35mm OD plastic pipe. This was the size of the waste outflow from the bathroom sink (B&Q). 8 layers of 200g uni, plus helical and 0-90 weave. This mandrel is still inside the tiller, which is only 2x layers of weave.

Tension Struts

Laid up on a bit of wood with a wedge at one end (mandrels CO Andy P and also the kirks) the struts were made of 10 layers of 300g uni. If made again I'd do 5 layers uni, 5 layers glass weave, 5 layers uni. Thicher, but then you would be able to grab them when in the water without fear of breakage…

⁴⁾

See Harry potter for an explanation of why a dis-used church hall in Bethnal Green that appeared from thin air, became our workshop and contained every tool needed to build a Cherub was thus named

fixing a bent aluminium mast

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

fixing a bent aluminium mast

When we were delivered Whaam! it had a bent mast that looked like this…

Then Ed and his grandad tryed to re-bend it but in the process ended up snapping it into 2 pieces

Yes… we did jump on it a bit!!!!!

Then after it was broken we had no choice but to put a patch around it..

As you can see. Underneath this patch, there is three stailess steel bars which are evenly spread around the inside of the mast and screwed right through. This is what provides the strength for the mast, with the patch alone, it would not stand up to the force of cherubing, and it would be dangerous to put hardly any rig tension on.

Boat Amnesty

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Boat Amnesty

According to Harvey Hillary there are at least 5 things wrong with every boat in a championship fleet. Each one of those things has the potential to slow the boat down. Writing down the problems that you find when sailing will make it more likely that you will fix them.

In the Cherub class I think most of us can find more than 5 things wrong with our boats. The Boat Amnesty page was created to give a place to list defects and to cross them off over the winter as they are repaired.

Natural Born Skiffers

Urgent work

~~Build a monolithic carbon mast foot instead of the sandwich one for confidence~~
~~Plug some holes! Holes drilled in transom to drain water from side tanks.~~
~~Add wheels to the trolley redo a new craddle~~

Repairs

~~Repair the jib track~~
Fair rudder and daggerboard
Reinforce the GNAV or why not imagine a double GNAV system to allow a nice main shape

Upgrades

~~Change the chute which was modified a pre-race friday night :D~~ Note the new one is working amazingly
Fill the gap between daggerboard and dagger case…
bias the wheelie bar for better downwind comfort
remove the paint and improve the hull fairing !
work on boat porn star finish …
change A2 rivets for A4 rivets on the mast and isolate them from the carbon.
adapt a stiffer mast head (2008) !
build a carbon toilet seat to respect a stupid late bet :D
build a new stiffer daggerboard
build a cleaner rudder
add a spinnaker sheet retrieve system linked whith the pole

Atum Bom

Repairs

Bottom of board is rough after collision with the bottom of weynouth harbour. DONE
Top back edge of the board is cracked after collision with crew's knee! DONE
Parrell beads on cunningham are too small to get over the mast heel reinforcements.
New progrip on gunwhales. DONE
Fix the chine damage from Corus. (oops!)

Upgrades

New T foil. DONE
Twisty grip. DONE
Outhaul has no calibration.
T foil has no calibration. DONE
Mainsail uptie could be better. DONE
Move kite turning block to back of kite sock. DONE
Ally kite hoop was carboned in and should be replaced.
Sort out trolley. DONE

Setup

Underaked mast. DONE
Probably too little rig tension.(<200kg) DONE
Stop the board from coming up with well placed attachment on floor. DONE
lengthen the main/jib sheet a bit, and/or deboing it. DONE
cut the excess from the trapezes.
Sort out D2 adjustment.

Primal Scream

Repair Accident Damage from Nationals

Wing, Gantry, Mast Bridge, False Floor DONE
T-foil wing split at tip DONE
Broken Jib batten DONE
Small tear in Jib

Other Work

Finish fitting out mast DONISH
1. Finalize mast foot
2. internalize spinnaker halliard.
Cunningham lead high friction change block routing possibly increase purchase DONE
T-Foil Adjustment needs extra purchase Extra purchase done
1. Continuous still to do
Centerboard stiff to move when fully down New deck sorted that one
Rudder Jams when partly down
Spinnaker Pole high friction Polished
Main sheet washes out of transom
Main sheet wraps around jammer.
Jib sheet cleat too close to centerboard
Needs paint tidying up

Ooops (again)

Urgent work

Finish snout.
Repair board bottom from hitting big rock in Weymouth.
Fill trailing edge of board, remove paint
Remove paint from rudder
GO SAILING

Huckle ...the Maori Hunter

Urgent work

Find a way of steering the boat! Rudder & stock snapped during last outing!!!
Plug some holes! Holes drilled in transom to drain water from side tanks.
Make the sides less slippery for the crew.

Repairs

Make/find/scab a new rudder stock and blade
Insert some bungs into the neatly drilled transom holes
Renovate light weight boom (heavy boom hurts my head too much!)
Make the cunningham work

Upgrades

give it a kite by fashioning a removable bowsprit that can be deck mounted and boom stored (for starters!!)

Slippery When Wet

Upgrades

Finish glassing Wheelie bars
Fit new smaller chute.
Fill in gap around smaller chute
Fit new bung holes
Strenthen Snout externally
Make longer pole
Re position Jib cleat (which gets in way of longer pole)

Fit Tfoil to rudder
Fit T foil control system to rudder stock

Repairs Strengthen side decks in way of shroud plates.

Making a Boom

anonymous@undisclosed.example.com (Anonymous) — Wed, 01 Mar 2023 19:01:35 +0000

Making a Boom

What follows are instructions on making a Carbon Boom for a Cherub, it is based on the techniques used at a Class Association organized Sticky Weekend where a boom was made for Paul Croote this was laid out step by step by phil kirk in an email and with additional information and tips from Dave Chisholm (aka Carbonology Dave) and from other build projects.

These instructions could be modified to build any other light weight tubular structure, however the reliability and suitability of this is dependent on the builders skill with the techniques described. The chemicals and tools used in building anything out of Carbon composite can be dangerous and appropriate safety measures should be taken.

This boom is build on the class three piece boom mandrel, which has been designed so that after construction the centre section can be slid out allowing the other two sections to be removed easily. It is not necessary to use a multi piece mandrel, however it can be difficult to get the finished tube off a one piece mandrel and there is more than one boom still attached to its mandrel.

Getting Started

Make sure you have all your materials, tooling, gloves and safety glasses to hand. Along with plenty of time and assistance as it always takes longer than you think and an extra pair of hands is useful.

Getting Slippy

rub mould release wax over all the surfaces of the mandrel especially between the three parts.
wrap mandrel with Mylar film and secure to itself with parcel tape. The Mylar moves easily over the waxed mandrel which will help you get it apart. To hold the Mylar film tube in place neatly Spiral wind parcel tape on over the top overlapping the previous turn.

Alternative 1: Neatly cover mandrel with parcel tape sticky side outwards. Then apply a second layer sticky side inwards. This should also slide off the waxed mandrel but with the greater number of spirals of tape can be difficult to keep neat.
Alternative 2: Try using polythene instead of Mylar and spiral wind parcel tape over it again keeping it neat can be difficult.

Note: you can't cover the three pieces of the mandrel directly with tape sticky side down. This will stop the centre section from coming out.

Wax the taped mandrel thoroughly.

Do not skimp on these stages as you will waste much more time trying to get a stuck mandrel out of your boom and may even ruin both the mandrel and the boom in the process.

Getting Sticky

The Lay up is done so that the thickness and so the strength of the laminate increases as you move forward along the boom. There is also extra cloth on the upper and lower sections of the boom as this is where the strain will be greatest so the extra cloth here be most effective in increasing the stiffness of the boom.

Depending on how the fittings are attached, the second highest load in a boom after the bending moment is torsional. The clew and mainsheet are rotating against the kicker, and the tube can twist itself to destruction. This means that as well as the Uni directional fibres along the length of the boom you need some off axis fibres to take the torsional loads.

The lay up is as follows:

200 gram plain weave full length of intended boom plus a bit (ensure each cloth overlaps itself by about 15-20mm when it is wrapped round the mandrel.) This layer can be cut so that the fibres run at 45 degrees helping to take the torsional loadings.
300 gram uni around the whole tube for the full length of intended boom plus a bit. - lay it up on the zero axis first, then tape one end so it can't rotate, then 'squew' it from the other end). 30degrees would be ideal, but 20 will be enough. You will still get a lot of compressional/tensional strength from it so you won't need to replace it add extra on axis fibres. Tape the far end so it will not untwist when you do the next layer.
300 gram uni full length of intended boom plus a bit as previous layer then squew but in the opposite direction.
300 gram uni strip for the full length along top an bottom sides of boom
300 gram uni strip for the full length along top an bottom sides of boom
300 gram uni strip along top and bottom of the boom to mainsheet take off point. (Round the outboard end of the cloth to avoid stress raisers) This would be variable depending on mainsheet setup i.e. with an aft mainsheet it may not be necessary
300 gram uni strip along top and bottom of boom to kicker take off point.
200 gram plain weave to give some hoop strength and to prevent the uni from peeling. (This can be added on a second laminating batch to give a factory shiny finish.)

To wet out cut some polythene sheet into strips wider than the circumference and slightly longer than the boom, the cloth is then wet out on the sheet which is then picked up and used to transfer the cloth over to the mandrel. The sheet is then peeled off the wet cloth layer and used again for the next one. The cloth can then get the last few tweaks in its position and the next layer added finally the lay-up needs to be consolidated.

Getting Squishy

With the lay-up in place it now needs to be consolidated to remove any air pockets and any excess resin. There are a number of different ways to do this depending on what you have available and what you plan to do next with your boom.

The proper stuff is “Heat shrink Tape” it will shrink by approx 10% when heat from a paint stripper heat gun is applied. Applied the right way around (outside of roll to the job) it has its own release agent and comes off so easily it's a joke. It should be applied in a tight spiral with quite a large overlap between each of the wraps with the tension kept as even as possible. It needs less heat to contract fully than parcel tape and therefore causes less damage to the matrix. It is typically sold in 100m rolls of 30mm wide tape.
Peel ply best cut into strips and wound around the tube in a spiral, you can get peel ply in rolls of tape 50mm wide which is ideal for this and other applications. Peel ply is good if you want to bond the tube to something else or if you want a grippy finish e.g. for a tiller extension. You can cut your own strips or lay it on length ways but it is difficult to keep it neat when doing this.
Use parcel tape as heat shrink tape. (Remember to make this up before hand by sticking two layers together stick sides together. make this in lengths and stick together with more tape. You will need quite a lot!

Length = circumference of boom * (length of boom / 1/2 width of tape). Stick one end of the heat shrink tape to the mandrel beyond the boom and wind firmly and careful until you reach the other.

When you heat the laminate up with the heat gun the tape will shrink removing air pockets and the now warm and runny resin will be squeezed out, sometimes at high pressure so wear eye protection.

Getting Fancy

When doing the laminate all in one go unless you are incredibly lucky and careful with the tension of the heat shrink tape you will end up with a few wrinkles and bumps in the surface. If you want to get the bling factory finish then you should leave the outer 200g plain weave layer till after you have filled and faired the surface.

Another tip if you want to do it all in one go is to use some sort of breather fabric or padding between the peel ply and the shrink tape on the first consolidation. We use cheap woven glass fibre (300g) or old vac bag breather. This prevents the shrink tape marking the structure at all, and spreads the loads so the way you apply the tape is less critical - most importantly you have less defects to sand out/fill before you put your top layer on. And if you use Glass then all your sanding is done on the glass so you do not turn your expensive structural Carbon into not very useful dust.

Once you have filled and sanded your base structure to perfection it is time to add the final layer of 200g cloth, getting the best finish is tricky and you need to be careful with the cloth so there are no pulled threads or wrinkles. This layer also needs to have UV protection or it will quickly dull and turn white. This can be done either by using a resin with built in UV protection such as SP115 or a couple of coats of clear PU varnish to provide the protection.

As they say on Blue Peter 'Here's one I made earlier'

Core Repair

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Core Repair

Whilst failures of the actual foam sandwich structure aren't common, they do happen. Here is how to recognise and fix these.

Delamination

The most basic would be delamination, where the skin has seperated from the core and just needs to be reattached. This can be a bit tricky to locate one of the best ways is to take a 50P peice and use it to tap the skin. By listening to the sound as you move it around it is possable to map the damaged area. If you are sure that the damage is confined to one skin then the repair can be done without too much disturbance.

With the area of damage mapped out it is possable to fill the void with a lightweight filler without cutting too much skin away. Carefully drill two holes one at each end of the damage and fill a syringe with the light weight mix of filler, then use it to squeeze the filler into one of the holes till it comes out the other indicating that the void is full. You may need to use some tape to hold the filler in there while you wait for it to cure then all that is required is to sand the exess flat, paint and job done.

Core Failure

Slightly more complex would be a core failure where the core itself has broken up, this could be caused by impact damage from a colision or long term damage such as the point where the boat rests on a trailer The outside skin may not be damage and from the outside you may not see anything very obvious. The symptom will be simply that an area of the boat is soft, and can be pushed up and down. The area can be maped again by taping and marking with a indelable marker.

Start by cutting out the outer skin above the soft area along the failure point. You can easily identify the area where the core has broken up and isn't attached to the outer skin - its often damp and soggy. You need to take out the core for all this area. Take it back to the inner skin. If you have a router (carpentry that is, not networking!) this is great for the job, otherwise you'll need to use a sharp chisel and take great care.

You also need to see what's going on with the inner skin. This may be cracked, or it may also have delaminated. If its delaminated or cracked beyond the area of core you've already removed then you've got to cut back more. You need to and up with the core securely stuck to skin on both sides all round the repair area. Don't worry within reason) if this is an irregular shape, we'll come to that in a minute. Make sure there#s at least a couple of centimetres of good skin inside the cut away foam.

With all the affected inner skin exposed take a good look at it. Its probably damaged or distorted. If this is the case then cut it back to a couple of centimeters away from the edge of the foam (see sketch). The rest will no longer be doing anything useful, so remove it.

Sand away the outer skin for a reasonable distance around your cut out area. This must be a high load area (otherwise it wouldn't have failed!), so a couple of centimetres of exposed foam plus a five cm of taper on the actual outer laminate (as opposed to paint) will do. Try not to sand back any more foam once the skin is off it (not very easy!). You do need to cut the laminate back for a feather join both for strength and so that you can sand back the repair so there are no bumps on the skin when you finish. This will be more work and take longer than you think!

With the inner skin exposed you can see what condition its in. Its quite likely that this will have split. You need to cut back the foam to expose all of the crack plus a suitable layer all round the crack, in order to reinforce it with new layup. If the foam is no longer stuck to the skin you need to cut back until you get back to solid construction. If the crack goes up to the chine you will need to cut away enough topside foam to get a good strong repair.

You won't need a huge amount of layup on the inner skin to repair the crack, depending on how damaged the glass is of course. Use similar weight and strength layup to the original skin, but do't go overboard. Cut the glass/carbon out ready, but don't glue it on until you're ready for the foam.

You want to get a piece of foam the same thickness and density as the original. If the area you're working on is quite flat you can just cut out a single piece. To get the shape - if its irregular - put a piece of paper over the hole and trace round the edges with a soft pencil like a brass rubbing! If you're working on a very curved area of skin though, it may be difficult to get the foam to sit flush with the inner skin (unless you have vacuum bagging capability). If so then divide it into a few pieces. When its all shaped to perfection and fits snugly with the minimum of gaps then it time to get the epoxy out. Glue on the inner skin reinforcement onto the foam as normal with some filler to fill the bubbles in the foam. Add some strong filler where it will touch the old inner skin, and while its all wet put it in the gap. The core needs to go in with the lightest possible filler mix round the edges, because this will give hard spots. Vacuum bag it down if you can, if not lots of tape, weight it down, or do what you can. Its essential that the new inner skin bonds well with the old inner skin or you will get problems and the job to do again.

When this has cured you'll probably find that the foam is slightly proud of the foam around it. Very proud if you sanded the old foam back too much. Bring it all flush, but be very careful of taking too much off. You are aiming to end up with a foam surface that's exactly where it was before the original outer skin went on. Now you're ready for the new outer skin. You want to use a smilar layup as for the orginal skin. Err on the strong side, but don't go way over the top though or you may get a “hard spot” which will crack at the edges. If you use more than one layer of cloth do successive patches in different sizes to spread the load and cover the area where you sanded back the outer skin. Consolidate it as well as you can. Finally fair and fill and then paint. If you've got everything right you won't be able to tell where it happened and all will be as good as new.

If you're lucky this will have happened in an area where you can get to the inside skin. If you're *very* lucky to be precise in these days of false floors. If so the same applies as above, except that you work from the inside and are much less worried about fairing off the surface!

Taken from an article originaly written by Jim Champ in 2003.

Craig Simon's Custard Truck

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Craig Simon's Custard Truck

These shots of the interior of an Australian Boat show some interesting differences in building practice. This is a predominantly glass boat (which is much better for photos!). Built mid 1990s.

Shell with Interior bulkheads. You can also spot the characteristic Australian Rigging cradle (don't know what they're really called). These have never been seen over in the UK, but they're a really neat idea. AIUI the boat lives in the cradle all the time off the water. If you look closely you can see how its shaped so that the boat can readily be rolled over on its side for rigging in the cradle with the gunwhales and bottom skin protected from even the most vicious of beaches.

Most British boats take the central spine right up to the bow. Note the extra reinforcement before the front bulkhead. This area takes a real hammering and was a notorious spot for trouble in the days of wood boats.

Montage of various interior details. Note how the gantry is inset from the transom. The ramped down false floor is a nice detail. This brings the transom bulkhead further in to support the false floor and reduces weight in the end slightly.

Front bulkhead and side tank bulkheads. There seems to be less framing at deck height than most British boats. The false floor has a layer of kevlar in the layup. Ths was intended (successfully) to give plenty of impact resistance for the abuse that the floor inevitably takes.

General view aft. Note the appreciable gunwhale overhang. This is a rule difference really as the Australian rules prohibit the reverse chine topside flare seen in the UK, but in both cases the aim is to have the topsides as vertical as possible to promote clean flow separation at the chines when planing.

Bow area. Unidirectional carbon where the rig loads will come.

Foredeck on. The mastgate looks designed to take substantial loads from the rig, and I suspect the foredeck is much more of a load bearing structure than in UK practice, where its more common to see more substantial internal space frame.

Building the side tanks. Nice radiused tank tops for comfort. The technique used was to cut strips of foam, tack them onto the frames with pins and glue them together in position. They were then pulled off and glassed on the inside, then glued in place and glassed on the outside.

Aft view showing the slots in the side deck foam clearly. Temporary brackets locate the deck while it cures. “Long and tedious but well worth it for the comfort factor!” says Craig!

Complete tanks. Carbon reinforcement where various fittings will be located.

All complete, painted, and waiting for all those expensive fittings…

All complete, ready to go sailing. Nice straightforward clean interior layout - but then that's pretty typical of all Cherubs anywhere.

And here it is. This shot is actually a few years on from brand new, and the extended rudder gantry is among the additions. The advantages of the rigging cradle in protecting the boat are obvious.

All photos © Craig Simons

Top Cherub Designers/Sailors talk about their boats.

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Top Cherub Designers/Sailors talk about their boats.

(Interview by Jim Champ in 2002)

The Cherub Class had some rule changes in 1997 which have had a significant effect on performance. The changes enabled the newer boats to be rather quicker in the lighter winds that have traditionally been the Achilles heel of the Cherub, without compromising the superb performance in sea breeze conditions. That this has been achieved is obvious in the recent drop in the PY number. Traditionally with a Cherub you won in a breeze and were last in F1, but the newer boats are proving competitive in moderate conditions too.

Gathered here are Andy Paterson, of Bloodaxe Boats, 2002 National Champion, in a series that ended up with a light airs bias, Robin Russell, last years winner in a fresh breeze series, together with his boat's designer Simon Roberts, and Gavin Sims, runner up this year in his new boat, exhibited at Sailboat in 2002, which was particularly strong in the mid wind range. They're talking about their own and each other's boats. Doing the interviewing is Class president Jim Champ.

JC Gavin, tell us about your boat

GS - The design is my own called “ButtPlug.” I built spars, foils, hull and cut the sails. Crew weight is towards the heavy end of the Cherub spectrum, 150kg (70kg crew, 80kg helm) Hull wise it has flat U-sections forward, going to very flat at the back. The chines are minimum length (2m), so the floor merges into the topsides almost back to the mast. The maximum chine beam is about 800mm from the transom I think but they hardly tuck in that much after that. There's very little rocker it's made to be flat for high planing speeds and very little rise of floor, again for top speed in flat water. It's not down to the minimum waterline beam though, when I drew it I didn't like the way a narrower boat would float with our crew weight. The U-sections forward are for light(non-trapezing) conditions as they should give slightly less wetted surface than carrying chines forward. The rudder gantry, well something different was nice!

Graphic One - Line Drawing of ButtPlus (Sims) Design.

Above the deck the carbon mast is evenly prebent throughout its length, with the bottom locked through the use of D2's (Check stays to the root of the lower spreaders). The mast is stepped at gooseneck height and the gooseneck mounted on an extended kingpost so the kicker has very little effect on mast bend. The rig is very rigid. The jib is cut quite flat, with a wider sheeting angle than most, and is self tacking with the sail leech roach giving minimal overlap.. The main is quite full for its chord but because it has a higher aspect than most it looks slightly flatter the luff is about 5.8m. The main is cut with a very straight exit at the leech. The rig has considerable rake, this coupled with the prebend makes the mast seem hooked to windward when viewed from apparent wind angle (as discussed in Bethwaite). It seems exceedingly quick and powered up on a 2-sailer, with no real gap between wiring with 2 sails quite deep and being able to hold the kite. The kite is masthead, and so with that tall mast it is very high aspect ratio. Basically I went for luff length (see Bethwaite again), and it seems to work all right, although it looks small. The rig doesn't seem very effective with the apparent wind aft of the beam, due to the rake and the fact that, because of the prebend, the upper part of the main tends to stay centrelined when the wind gets down towards the 5 knot region.

JC When you designed/setup your boat what were the major considerations?

GS Well it needed to be faster than my last boat (Dangerous Strawberry)! Simon (my crew) said to me whilst I was designing “make it as extreme as you want, we can always find a way to sail it.” But I chickened out from my first try and made it tamer. The rig is slightly further aft than the norm (I think), again this coupled with the rake and prebend is what I think makes it a demon on a 2 sailer. Also putting the mast back allowed me to keep the bow entry angle down whilst achieving a reasonable beam where the cockpit starts/chine starts. This also allowed for a slightly longer kite pole (as it's on the centreline it can only go as far back as mast) and a longer kite luff, which should make downwind quicker. Structurally it's fairly standard (same as the Slug I think) but thinner foam was used (cheaper). I decided to build an extended kingpost with integral lower shrouds primarily to lower the all up weight. This could be included in the hull weight and so a lighter mast would be required. It also stiffened up the hull considerably it's effectively twice as deep in that area as a conventional boat. With the rig I wanted to keep with what I had started with Dangerous Strawberry (Dangerous Strawberry has a very radical tall rig with around a 6.1m luff). But Strawberry had a drawback in the medium wind strengths, the short chord on the main (and very flat cut) meant that it was impossible to get the leech to stand firm, so upwind pointing and speed was lost. Therefore I shortened the mast by about 30cm to give more chord (foot is also slightly higher inboard) and made sure the sails were full enough. Looking down the mast of a prebent rig compared to a straight one, the main looks more right without having to pile on the sheet and kicker (only if the sail's luff is cut for that curve). I used monofilm to make the sails because it is cheap. It seems to have lasted a season fine. The jib is probably too flat as it stalls out in the very light stuff (i.e. end of nationals).

JC Robin, what about your boat? The Slug's a bit older I guess, 1998 wasn't it?

Photo 2 Green Slug (Robin Russel & Will Lee) Photo © Jim Champ

RR I suppose but it's on no way obsolescent, just a slightly different approach, but I'd better let Simon talk about the hull shape. The boat is home built by me, with a Proctor/Batt sails rig, and we're right at the top of the weight range with around 160kg between us. On the rig I've gone for a fair amount of rake, max. width shroud base with long spreaders, and moderate rig tension compared to some. The mainsail profile is a moderate (by Cherub standards) elliptical profile, with plenty of roach but not as fat at the top as some of the more extreme rigs. The luff is around 5.4m going to 5.49m with the cunningham right down. The chord is greater at the foot than the narrower sails favoured by Andy and Gavin. The rig is basically a logical development of the rigs on my previous boats, with some observations from others. Apart from the long spreaders the “solid lowers” are one of the more distinctive features. This locks the mast up at gooseneck level in the same way as Gavin's post does, but with more scope for changes of course.

The hull – well, low but some rocker, minimum width @ about 7-8ft, fair amount of curvature across deadrise, fairly parallel running aft compared to other boats.

Graphic 2 - Slug (Roberts mk3) Design

JC - Simon, what are your thoughts on the shape? It was a development of my previous design, the Dog. The main aim was to keep the same basic form but remove some of the volume around the 3 to 4 ft station. This was an attempt to improve its upwind performance in chop, where the Dog tended to slam too much. The changes in chine beam measurement allowed the max. beam to move aft and allow the volume to be removed from the front sections.

JC and you Andy. This is the fourth year for your Mk 7, and it's probably the most numerous of the 97 rules shapes there's even one being built in the States.

AP Two being built in the US in fact, with plans having gone to Croatia and Holland too! Yes, there are more of these than any of my other Cherub designs, although there are a lot more Axeman Moths. The hull and foils are Bloodaxe carbon of course, the mast is Superspars and the sails are from Caws. We had 135kg on board in the Nationals 75+60 respectively, which is middle to light end of the range for Cherubs.

The hull is boxy, with low chines carried through to the bottom of the stem and low rise of floor. It's got more vertical topsides than the other boats, high freeboard and a moderate even rocker line. The entry is fine with a constant entry angle from the base to the top of the stem, it's not flared at all above the waterline. The transom is narrow with the chines curving inwards in plan view. It's also much simpler in construction. By doing away with sidedecks, only having transverse frames and the crew working on the inner skin of the hull above the false floor there's am awful lot less structure, although what there is has to be beefed up with thicker foam and all carbon skins to keep the stiffness in the boat. Graphic 3 Paterson mk7 Design

JC and the rig?

AP It's very much a development of the rig on my previous boat, but lighter with the carbon mast. There are no check stays, I've found them unnecessary as the mid spreaders are set up with forward deflection to keep the lower mast straight. The upper spreaders on the other hand are raked back about 45 degrees to induce plenty of topmast pre-bend. The caps come through the upper spreaders, the mid spreaders about halfway along and then down to the gooseneck to keep the mast stiff sideways. The mainsail luff is longer than average at about 5.5m, and the mainsail is virtually flat topped with plenty of roach. The masthead kite is fairly narrow. This rig (combined with hull shape) gives the advantage of sailing deeper downwind than the rest of the fleet, but at the same boat speed. The disadvantage of the high rig/ flat hull shape and low crew weight combination is that it is very difficult to tight 3-sail-reach in any breeze with the kite up. Shiny Beast Shiny Beast (Andy Paterson & Ross Clark) Photo © Castle Photography.

The Cherub Class does not own rights for this far superior photo of Shiny Beast beyond the Class Website

JC What were your thoughts when you designed the boat? It's certainly been the most successful of your Cherubs.

AP Light weather performance was top of the pile traditionally a Cherub weakness. I was looking to increase power in the rig in light/moderate conditions, but still be able to flatten off the rig and depower without flapping the main when it's windy. The long luff masthead kite is intended to increase downwind power and allow lower angles to be sailed at top speed. The hull is developed from Mk 6, but the '97 rule change gave freedom to reduce the chine beam, and to move the position of max. chine beam aft to make the entry finer. The shape is designed to plane early, with large flat areas under the mast. The moderate rocker and curvy chines aid control at high speed and avoid nosediving. Its narrow forward so that hull doesn't slow in a nosedive. The narrow entry and high freeboard at the bow allow the boat to be driven hard upwind and downwind in waves. The hull was designed to be sailed in the (home club) Solent waves, where steep wind over tide waves can catch out the fuller bow designs. The simplistic hull construction enabled me to reduce hull weight and carry max. correctors to reduce inertia and weight in the bow.

JC So much for your own boats, how do you rate them against each other?

GS Well, Andy P is good when its light, but Patrick [also with a Paterson 7 and a similar rig] has the ability to go faster I think. But AquaMarina [another Paterson 7 owned by Phil Alderson] was going fast enough when it was windier. He has a different rig which is more like Robins and is a bit heavier crew as well. In all though I think the Paterson is more suited to the lighter stuff.

I was pleased with my boat. It's definitely fast in the moderate wind range, from semi trapezing up to flat out, but it is very sensitive to heel. Gybing is a dream, especially with the high aspect ratio kite and clean cockpit. It's better than my previous boat, a Bistro, which is not regarded as a tricky Cherub design to sail. The Slug now looks fairly moderate compared to other 97 rules designs, probably because it has a wide foredeck. The relatively high rise of floor makes it quite tolerant of heel and waves and therefore it's probably the easiest to sail when the wind is up, therefore enabling the crew to push harder.

RR - Really they're all much of a muchness I don't think you can put the differences all down to the boats. The Patersons seem to fare well in light stuff, Gavin's seems OK in all conditions and I wouldn't write the Slug off in light airs in the right hands.

JC yes, we haven't really seen a Slug with a light crew have we?

SR The Paterson seems OK. Goes well in light wind but I think that may be strongly aided by the crews. fairly average in winds over 10/12 knots. The Sims seems fine, but I haven't really seen it in many conditions. I think the Slug is good except in light wind where the transom sinks too much to be quick. It seems to plane fairly early and fairly fast and upwind it is significantly better than Dog especially in choppy water. I would guess it's the fastest design around with the possible exception of Mango Jam.

AP My boat is hard to sail. It has to be sailed very flat. It's excellent in light winds and also in moderate conditions (but we had no nice moderate races this year)! With more crew weight, and less falling in, it would be more competitive in strong winds. Gavin's boat was good in all conditions, and of course Robin goes very well in a breeze.

JC so what would you put the performance differences down to?

RR Crew, crew crew!

AP The light crews are at disadvantage in strong winds compared to the heavies, but in light winds the heavies/wide boats are at a BIG disadvantage. e.g. Robin and Dave [Roe] 1st/2nd in windy races, then barely top ten in the light stuff, but we and Patrick were 1st/2nd in light races, but only down to 4th ish places in the windy stuff. The tall rig that I (and Patrick) use with a square top main, large roach, masthead kite, flat sails was significant.. Phil Alderson performed best in moderate winds with a different rig (which in many ways is more like Robin's rig in concept). Hull shape has got a lot to do with it too, and low all up weight. Gavin's boat seems basically similar to Pat7 in concept, while the Slug gains in a breeze from being easier to sail, the lower aspect rig and high crew weight.

SR – On the P7 the heavy U bow combined with very little curvature. Should have very straight water planes and low wetted surface. Probably makes it a hand full in strong winds and unlikely to be quick when it starts to pop out of the water upwind. I'm not really familiar enough with Gavin's boat to comment too much. As for the Slug, well it's not very radical in any way. There is enough curvature to make it fairly manageable in most wind but still flat enough to plane early. The thinner bows make it much easier to drive up wind through slop and so it doesn't slow down in the same way as a Dog/Bistro/Frenzy etc.

GS Andy and Patrick's light weight both contribute to their light airs performance. Their Caws rigs are very flat which I reckon also helps. But the hull is the major factor I think, the maximum chine beam nearer to the centreline, with the even rocker throughout and the narrow transom coupled with a mast relatively far forward in the boat enable the crew to get forward and sail with a clean wake in non planing conditions. My rig I think seems to get powered up sooner than the rest, and the hull seems to plane nicely. It suits flat water (i.e. Bala and the second day of Nationals). Robin and Will's available righting moment allow them to power away from everyone when the breeze is up. They just drive hard and go.

JC so what's most significant? What should someone planning a new boat concentrate on?

GS I would say the hull is a big decision, as that is what makes these three different. The rigs aren't that different, but crew weight is. Andy's boat is optimised for the light stuff at least in Cherub terms , mine is for when as soon as there is enough wind to wire, and the Slug is the all-rounder. It's just that coupled with the crew weight of Robin and Will the Slug needs wind.

AP There's no doubt that in light winds the Paterson 7 hull shape is faster… in the light last race, Pat7's were 1,2,3 on the water. The crew weight on the Slug gave them significant advantage in strong winds, but also the crew ability! They were the only boat not fall in the windy races.

SR – Certainly the Paterson 7 seem to be a hull shape that suits light breeze, but on the other hand most of the people sailing them are light and seem to be good light winds sailors. I don't think the shape will work well in any wind though. The Sims looks like a good shape, and I think it should go well in the medium stuff as it looks flat, but I've not really studied it much. My guess is it should go in a breeze as it seems like a flatter Slug. Could be slightly harder to sail though. The Slug is fairly easy to sail in a breeze so you can push it quite hard. I think it should go well in medium breeze though given the right crew. At the moment both Robin/Will and Andy/Me go well in strong wind but that is largely down to lard and enjoyment. The Dog was a good medium wind boat and I would expect the Slug to be similar. Gavin's boat may have the edge in medium but I don't think that it will be by much if any.

JC Where do you see us going from here? Where do you think the next big gains will come?

GS - I think rigs. Plenty more playing to be done. Wing masts. Hulls will get faster, but only in incremental steps, unless there is a change to the minimum weight. Foils, hmm not gonna make that much difference unless someone discovers something new. I don't think hydrofoils will find their way in, not the t-foil type things the 14's have. The thing is that Cherubs are heavily optimised for flat out planing speeds. I have wondered what a National Twelve style hull would go like in the sub 10 knot wind range, but all the F4, 5 and 6 jumping is too much to miss out on.

RR Wing masts, tall rigs for light airs. Weight.

AP less weight!!

JC at this point I guess I should note for readers that there's a general acceptance that the minimum weight for the Cherub, which has been much the same at 110lbs/50kg for the last 50 years, is due to drop. The majority of new boats are carrying lead, which is hardly in the spirit of the class. The concern is at what point the technology and skills out there will progress so that a first time builder will normally get within a few pounds of the new minimum.

AP And more rig development e.g. your rig seems the best new 'thing'. [The president's boat has just been upgraded with a New Zealand made C-tech/Fyfe Sails rig with a 5.9m luff. It's straight up to the hounds with plenty of prebend above.] More hull designs along the lines of Pat 7 and Sims (and, sort of, Squid) to refine the performance We need more boats to tell if it's hull, rig or crew.

Its interesting to note that versus “conventional” boats like the RS and Laser products our light wind speed is poor, and our outstanding performance comes in at F2/3, when we are full powered up upwind and downwind, and are planing along, apparent wind sailing, whilst the heavier boats are still not powered or fast. (exception of course is RS 700 which has more sail, more length and less all up weight when you include the crew! My design/rig/crew weight is optimised for these 'average' conditions, but this seems to make it a light wind flyer vs. other cherubs.

SR Rig changes. I think the Slug/Sims hulls are moving towards a good all round shape though there a bound to be some improvements which can be made. Also there will be more extreme shapes which suit certain conditions but a slightly flatter Slug or tweaked Sims seems a logical conclusion to me. Rigs are much more open to exploit. Maybe wing masts but certainly there should be room to improve the current rigs. Still much variation in luff length roach & ellipse/square plan form within the fleet`. My guess is we will move towards rigs similar in plan to Fyfe and maybe sleeve luff/wing mast.

JC - Thanks all. One interesting point is on optimising boats for conditions Andy, you seem to me to have designed his boat as much as anything to be competitive in handicap club racing. You've dropped a bit of performance from the top end (winning races by 10 minutes is over the top if 5 minutes will do). The result is a boat which by Cherub standards is somewhat polarised to light airs, but in terms of a handicap event like Cowes Dinghy Week is strong in medium and heavy winds. In a fleet which notoriously likes to do multi-class events it will be interesting to see what decisions others make. We're in for an interesting few year's development (as usual)!.

Credit

Words: Jim Champ

Designing Cherubs

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Designing Cherubs

Boat design is a serious business which is not to be undertaken lightly. After all, even professionals get it badly wrong a lot of the time.

Uk Cherub Class Rules 2005 Always a good place to start when designing a boat! If you are in any doubt about the meaning or possible interpretation of any aspect of the rules please do not hesistate to contact the Technical Officer, Measurement Officer or any member of the Committee.

Top Cherub Designers/Sailors talk about their boats. Pick up tips from the best.

Designing your own Cherub

Disclaimer This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. Its also very much based on how this amateur goes about drawing boats. A trained professional will doubtless approach things differently. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here.
I should also point out that I've never built a Cherub to any of my paper designs*, although I have built a one-off singlehander.

One of the aims of the Cherub Class has always been to provide a platform for people to design their own boats. Quite a few careers have started with designing Cherubs and related boats. John Spencer was the first, the original Cherub being the start of his career, but Russ Bowler, Iain Murray, various Bethwaites and the UK's Andy Paterson all had Cherubs at or near the start of careers that have included significant designs in other classes. There are quite a few ways of going about designing boats, and those of you with appropriate training will be able to make your own choices. Apart from the obvious choices of naval architecture and mechanical engineering quite a few successful designers had trained as civil architects.

Some thoughts on design extremes.

People's first boats tend to be extreme. Obviously you want to go with your ideas, and there's no point in doing what Uffa Fox did, which was not to put his radical ideas in practice until his third 14 footer, the legendary groundbreaker 'Avenger'. On the other hand you don't really want to end up with a boat that is way out on a limb and only effective in some conditions (as I rather fear I did with my one off single hander). Off hand though I can only think of one first boat in recent years which was an unqualified success - the Italian Bistro. So its probably worth considering designing both your radical new idea and a moderate version of it, and take a long hard look at both before deciding which one to build.

Balance is Everything

Julian Bethwaite will tell you that the most important thing he does is to travel with his eyes open and his mouth shut. You'll also find that you start drawing you don't really know what a boat looks like. It sounds ridiculous until you try and draw a familiar boat like a Laser from memory… Look at the whole picture. Think about where you will be sailing the boat, how heavy you are, whether you are brilliant boat handlers who can manage a tricky boat or whether you'd be faster in a stabler platform. Think about the rig you are going to put on. The rig needs to match the hull needs to match the crew needs to match the foils needs to match the rig…

Start with an Idea

The most important thing is to be familiar with Cherubs, to have sailed in the class and observed how different boats behave, and how you see the benefits of different shapes. Its also helpful to have a starting point - “What I'd like is a boat a bit like an Italian Bistro, but finer at the bow, narrower and with the beam further aft”. Maybe you get a sketch like this:

Make Sketches

From there I suggest you arm yourself with a drawing of your starting point and a sketch pad and start sketching ideas. It's important to consider the boat as a whole, not just as sections, profile etc. In order to do this I find it useful to draw waterline and to a lesser extent buttock sections through the boat. You also should have a good idea about how you want the waterlines and buttock lines to look, because this is how the water is flowing past your boat, which in the end is what is most important. I usually start by drawing sections, and then work out the waterlines from them, and then modify the waterlines to nearer what I think I want and alter the sections to suit. Through a few dozen pages of sketches you are getting a fairly good idea about what your boat will look like.

You'll find as you go through the sketches that your ideas will change, especially as you start converting sections into waterlines and vice versa and get a real feel for how the different factors inter-relate to make a complete boat. Once you get past the initial sketches graph paper starts making a lot of sense for this business of matching sections to waterlines and back again. It sounds like a lot of work - and it is. You need to be thorough though - you are going to be building this boat for six months or more and maybe sailing it for five years. It's a long time to be saying to yourself that you wish you'd thought more about the transom. You want to be able to visualise the underwater shape of the complete boat before you get past this stage.

Detailed Scale Drawings

At this stage most of us will want to turn to the computer and a drawing package. To a large extent it probably doesn't matter what you use, but the Australian Package Hullform, from Blue Peter Software, has been used for at least one Nationals winning Cherub. What you are using the package for is basically as a tool to do some of the donkeywork of mathematical calculations and of fairing lines and sections. Simon Roberts and Dave Roe both use their own custom computer drawing systems for boats, which they've steadily evolved to suit their particular requirements. The Italian Bistro was actually designed on a high-end programmable calculator. Alternatively - and especially if you have the required technical capability - you may prefer to carry on with pencil and paper, but perhaps move to larger scale drawings and a proper drawing board. Julian Bethwaite is certainly one top designer who's a firm advocate of staying clear of the computer. Perhaps at this stage - or better still while you were sketching - you first come across a nasty surprise when you discover that some of your most prized ideas won't work together. When I drew my first Cherub I wanted a flat midsection with lots of turn up near the chines, a V section bow, and straight waterlines in the bow with no lumps and hollows. I discovered you can't get that. With straight waterlines a flat mid section gives you a flat-bottomed bow. So you have to start making compromises. Perhaps three quarters of the art of sailboat design is the art of selecting the best compromises!

I don't propose to produce a manual to using Hullform, but note that Cherubs are quite tricky boats to put into a hull design package. You will need to get into the program thoroughly and use some of the subtler features to get the best out of it. This especially applies when drawing the deck line and snout area, where most Cherubs have angles and straight lines that the default settings of the program don't handle well. I also advise you to get into a regular regime of saving new copies of your drawing so that you have old versions to look at and maybe go back to if a particular idea doesn't work out. Its also good to get a version of your master design - and maybe one or two others - into the package so that you have a starting point for looking at the figures that it produces for you.

The major advantage of using a computer is that the process of fairing the sections can be automated, and also that you can do any number of “what if” variations on a theme and evaluate them. However a significant disadvantage is that it is all too easy to make a change in one place that affects another part of the hull through the fairing process, which you may miss. Another factor is that changes that look quite small on a computer screen can turn out to be some inches on the finished boat.

Models

I have ony ever heard of one Cherub design being tank tested, and you're not going to have the facilities yourself (unless you're studying Ship Science at Southampton, in which case I imagine reading this article is unnecessary). However I still find it useful to build a balsa wood and cardboard model of my design, just so that I can look at it from different directions and get a real feel for what the finished boat will look like. I'd especially (bitter experience here folks) make sure you build a model of your final design. I didn't for the single hander, and I suspect that if I had I might have started getting worried about just how flat it looked. As it was I didn't really get concerned until I saw the building jig - at which point it was a bit late! The intermediate design that I did build the model of had a lot more rocker…

Go For It

You don't really know how satisfying it is to have a boat that you have designed yourself until you get in it and sail it. Even though my singlehander is less than a complete success I don't regret doing it at all. And maybe next time I'll get it right!

Starting Points

I hope to have a few designs available electronically to give a starting point.

Design Drawings

There is a 1994 1994 design with flares and snout added to 97 rules and a 97 rules boat which I've sketched out, loosely based on a Bistro as outlined above. Its not remotely “ready to build” and almost certainly not quick, so be warned!

Coming later should be Dave Roe's Pasta Frenzy design - when I can make an electronic version.

Jim Champ, 2000

*Though I wish I'd got round to building my 1978 Cherub design- when I look at the drawings it bears a distinct resemblance to the highly successful mid 80s Kiwi design Tasman Express!

Recent Design 2000's - Now

anonymous@undisclosed.example.com (Anonymous) — Wed, 15 Mar 2023 18:51:21 +0000

Recent Design 2000's - Now

Don’t Do it

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Don’t Do it

There are some things that you should never do when maintaining a Cherub. At least not if you want to keep on sailing reliably and finishing even winning races

It will never hold

Never attach fittings to your foam boat with wood screws, it just does not work, they will pull out. You may say it is OK if you use a wooden backing piece and the fitting is low load, but you are taking a risk the wood will absorb water and get soft, the fitting will pull out it just takes time.

Never bolt high load fittings to a foam sandwich panel without a large washer or backing plate or at least replacing the foam with a plug of filler. The foam will crush and it will break.

It will always leak

Never fit a hatch cover to a curved deck. Hatch covers tend to leak at the best of times and if you are trying to fit it to a bit of deck that is not flat then it will always leak.

Never skimp on the thickness of the centreboard case. The centreboard case takes loads of abuse and once the boat has been built it is difficult to get to, so there is no point in saving a few grams by building the case super flimsy. Any weight you save there will more than be made up a couple of years down the line by a small leak that you can’t fix.

Never build your boat without a breather hole. When you put your hot boat down on a cold sea the air in it will contract reducing the pressure inside the hull, this will help water find its way in through the smallest hole or crack. In a bad case on a very hot day it may even damage the deck or hull.

It will not last

Never tie string to a pressed shackle or deck eye. If there is any movement in the string the sharp edges of the fitting will saw through the string, if lightly loaded it may last a few months, but heavily loaded it may not last the day! Use a forged shackle or thimble on the eyelet an it will last a lifetime.

Never attach Aluminium to Carbon, The aluminium will corrode through in no time.

It will just be heavy

Fair your boat with car body filler, it does not stick well to the epoxy and is extremely heavy. The short cure times are just not worth it.

Wetout directly onto a foam core, you are just pushing resin down into the voids in the core, margarine the core first with a lightweight mix of filler

Never stop worrying about weight, Every little bit of your boat that build adds weight and it is hard to get rid of.

It wont be strong

Never forget about triangles, Triangles make structures strong, forget about them at your peril.

Never forget about fiber orientation, Fibers are only strong along their length, at 90 degrees they have no strength. So make sure the majority are pointing in the direction of the load.

Fittings and Hard Points

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Fittings and Hard Points

Attaching fittings to a boat built out of light weight foam sandwich is not that difficult, however if not done properly then they will tend to move, leak and then pull out. This could take a few years or it could happen the first time you hit the water. Foam Sandwich is a great material for boats, as it produces stiff light panels, however they are not good when it comes to point loads, a small point load will tend to damage the thin skins, it can crush the delicate foam core and eventually fail. The key to attaching fittings is to spread the load out over a larger area protecting the soft core.

Screws and Bolts

Avoid using wood screws wherever possible, they rely on only a small contact area of the thread to grip, this works OK in a high density wood but in low density foam they will just pull out, particularly if the fitting is loaded in tension

Plywood core

During construction the core is locally replaced with plywood. This gives a strong area to bolt or even screw fittings to, however overtime the plywood will absorb water and rot.

High Density Foam

Core Replacement

The holes for the fitting are drilled through the top skin of the sandwich only, then using an allen key in a drill the foam is crushed around the holes, the voids are filled with filler and the fitting can be bolted in place.

Carbon/glass Backing plates

In areas where access to both sides of the structure is possible you can cut out a section of 3-4 mm thick carbon or glass plate slightly larger than the fitting to be attached, this spreads the load over a larger area.

Fronting Plates

A backing plate is made up and the fitting bolted to it, the bolts are then cut to length and the nuts bonded to the backing plate. This plate with nuts on is then bonded to the deck of the boat and glassed over the top. As the nuts are now captive the fitting can be removed and replaced as necessary. This is particularly on the false floor of a boat where you cannot get to the inside.

Tying with Carbon

This is where you bond a fitting in place with Carbon, this is often done by wrapping Carbon uni's around the fitting and a handy tubular part of the boat, this can be good for forestay and shroud points. You could loop around the mast stump for the kicker or around the boom for the kicker. It is also possible to just use small sections of woven cloth to bond lighter loaded parts onto the hull and spars. This is particularly handy for putting small fittings onto booms and masts where you want to avoid drilling holes.

Tying with String

Self explanatory but with the number of blocks that are designed specifically for tying in place it might be worth designing in some points that they can be tied to rather than adding weight by bolting a fitting in place and tying to that.

Building in Foam Sandwich

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Building in Foam Sandwich

Disclaimer

This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. “Best practice” also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a composite boat without someone experienced in the materials to contact for advice

Why Foam Sandwich.

The first thing to realise about foam sandwich construction is that it is easier for the amateur to build a strong light foam sandwich Cherub than it is to build a plywood one. The second thing to realise is that the materials involved are inherently more hostile to humans than those used in building wooden boats, and rather more handling precautions need to be taken. This is especially true for those of us who are used to being up to our wrists in Aerolite 306, with no greater precautions than a bucket of water to wash off acid spills (not that such practices are a good idea). There are two stages in building a foam boat. The first stage is to build the mould or jig that the hull is to be made about, and the second is the construction of the boat itself. The alternatives are to build the boat from a female mould, a male mould or a jig. Building a female mould is a very lengthy business, as it involves making a complete model of the finished boat, absolutely fair, or taking a mould off an existing boat. Renoving the boat from the mould when finished can bring its problems too. However the finished boat needs minimal fairing and finishing, which is why this is the preferred option for batch or series production of multiple boats. A male mould is used if the boat is to be vacuum bagged. If you have vacuum bagging facilities available - and there are ways and means of doing it on the cheap using old freezer pump motors etc - then you won't need me to tell you about the advantages. A male jig - which consists of battens over frames without a solid surface- is used when the layup will be hand consolidated. This is the most popular and probably the simplest option.

Planning the project.

This is vitally important with a foam boat. Whereas with a wood boat you can move fittings about easily, on a foam boat it's a good idea to have plywood or high density foam pads built in at an early stage. It is possible to do this later, but it's hassle. Before you start work out your internal layout as best you can, including any likely changes in the future (!) and draw up a diagram showing exactly where you are likely to want fittings. You can neither screw nor bolt fittings into foam sandwich, no matter how big a backing plate you put on. Building the Jig.

It is often possible to borrow a jig from someone else who has made a boat. In the UK most jigs seem to be used quite a number of times. However if you are building to your own design you have no choice. Spend a considerable amount of time on this. if the mould is not true, fair and symmetrical then the final boat won't be - one or two of the early Bistros are a little crooked about the transom at deck level for this very reason. The mould is normally constructed of 12mm plywood formers at 12“ intervals with battens at reasonably close intervals. Mark out the plywood formers using templates drawn on drafting film, not forgetting to allow for the thickness of your battens. Also build a ply keel former (longitudinal). This is used to help align all the transverse formers. The formers should be screwed down to a pair of rails, 4” by 2“ is adequate, to keep the whole thing solid. Once you are confident that they are all in exactly the correct place you can start putting on the battens. 1/2” square is perfectly adequate for these. Start with the chines gunwales and centre line, double and triple checking that everything is fair. They are best screwed down so you can alter them. Once the main battens are in you should put in sufficient others to support any large areas of foam, especially in areas like the underside where space is critical. Once they are all on it is a case of sanding and adjusting until you have exactly the shape you want. After some 4 months graft you will be in the same position as the someone who is borrowing a jig! If you have vacuum bagging facilities then there are considerable advantages in constructing a male mould, basically just by putting a layer of plywood over the battens. This is filled and faired, covered with parcel tape and then inner skin, foam and outer skin successively bagged down on top of this.

Picture - Part Built Boat [Photo - Paterson 7 under construction © Bloodaxe Boats]

The jig needs to be at a reasonable working height. On the one hand you need to be easily able to work on the middle of the hull, but on the other hand you don't want to have to bend down all the time.

Materials.

One advantage of being an amateur is that time is less of a constraint. If a pro goes a couple of days over building a boat than he doesn't eat for a few days, whereas an amateur just doesn't get to sail so quickly. Therefore there is less need to compromise on materials in favour of speedy construction. The other factor is that you are saving so much money on the cost of a new boat that it is easier to spend a bit more money on the constituents. Foam.

8mm or 10 mm Airex, Termanto or Divinycell is normally used. If you have both then use the thicker gauge for high load areas such as the space frame and the bottom of the hull. The hull floor and the false floor should be 75/80kg/m3 for dent resistance, but 55kg/m3 is adequate for topsides and other verticals. Many people use the same density throughout. Use the heavy foam for sidedecks and anything else likely to be exposed to the dreaded trapeze hook! Pads for fittings can be made from 200kg/m3 foam. The size of the bubbles in the foam and thus the hollows in the outer surface will affect how much resin and filler you use, and thus the weight and cost of the boat. Airex is generally considered best for this.

Fibres.

Rudyard Kipling wrote “There are nine and sixty ways of constructing tribal lays And every single one of them is right!”

Exactly the same applies to Cherub fibre lay-ups these days. If you talk to people about fibre lay-ups you will get about as many opinions as people you ask, some of them contradictory! There are several choices of fibre lay-up that will work well. Most boats now are either glass with local carbon or all carbon, but part Kevlar lay-ups have their fans too and certainly seem to lead to bullet-proof boats. The different fibre combinations have different characteristics, and different people seem to have different experiences. Kevlar is always a pain to wet out, and cannot be sanded, but has superb impact resistance. Carbon can give wetting out problems, isn't too great on impact resistance, sands well and provides the stiffest boat. E Glass is cheap and easy to work with, with reasonable impact resistance. Glass is probably the best choice for a first boat with a hand consolidated wet lay-up. All-carbon boats are much better vacuum bagged. All else being equal a glass boat will come out about 5kg heavier than a carbon one, but you should still easily be able to get under the minimum weight limit.

Glass.

There are two lay-ups in common use, one being two layers of 200g/m2 E-glass on the outer shell inside and out, and the other 1 layer of 300g/m2 with a second layer on the outside skin only over the bottom of the hull. The main fibres should be arranged at 45 degrees to the centreline, but where there are two layers the second layer should be 0/90. The best weaves to use are either 45/45 bi-directional or crows foot. Bi-directional is strongest and easy to use. Crows foot weave is very easy to shape and might be a bit cheaper. Standard weave is difficult to get to run over corners and chines, and also weakest. It's a good idea to add some local carbon reinforcement to an all glass shell. Unidirectional carbon tape is the favourite, as it is very easy to use. It should go in the areas subject to heavy loads from the rigging, front bulkheads, space frames etc. You should put it under the outer layer of glass in order to avoid sanding it all off again when you fair the boat.

Carbon.

A good lay-up is 200g/m² carbon plain weave, inner skin at ±45°, outer skin at ±45° with an extra layer at 0°/90° over bottom, 500mm from stem to 1m from the transom. Then add a thin layer of 100g/m² glass which adds thickness and protects the carbon from being removed during the fairing/sanding process…- if it goes black, stop sanding!

Kevlar/Carbon

If you want to go for a Kevlar skin on the undersurface - and this could be a good idea if you launch on lots of stones and the boat gets bashed a lot, then use the above lay-up, substituting a skin of 165g/m2 Kevlar for the 0°/90° carbon layer above, and run it from stem to stern. You need to be especially careful in the fairing stage to make sure that you don't cut through the glass into the Kevlar, because the ends of Kevlar will not sand off, but stick out through the fibre as a light fuzz. Not Smooth.

Resin.

The major choice is between polyester and epoxy. Polyester is cheaper and easier to use, Epoxy is more expensive, but makes for a much longer lived boat. Polyester also smells absolutely disgusting, and as far as I am concerned is right out if you are building the boat in the living room or a garage attached to the house. On the other hand epoxy is mildly carcinogenic and can cause allergic reactions, but in both cases it is important not to get the stuff on your hands. Barrier cream and plastic gloves are firmly recommended. Epoxy is recommended unless money is really tight or for some reason (perhaps a wild idea you want to try) you're not that bothered about longevity. In any case only use polyeseter with a primarily glass boat. Scott Bader (Strand Plastics) are a good supplier for polyester resin and SP Systems are most commonly used for Epoxy.

There are many epoxy resin formulations and the one you should use does depend on your facilities. SP Ampreg 20 is the most commonly used. However if your are vacuum bagging Ampreg 22 has advantages in health and safety terms provided that you have a heated workshop - it can get very viscous at low temperatures, and especially provided that you can keep it stored at an even temperature. It reacts very badly to getting cold, although all epoxy formulations will suffer if stored outside their recommended range.

Epoxy resins like to be post cured, which basically means heating the structure up quite a bit for an extended period of time. There is much more in the suppliers' handouts and technical documents - here are some references.

Building The Boat.

Attaching the foam to the jig.

First cover the jig with plastic sheet to stop the foam getting glued to the jig - most embarrassing. Obviously don't get any wrinkles on the battens because it will stop you fastening it down properly. Next attach the foam. Tie it on with wire, the handiest to use is probably 1.5mm PVC coated (inner core of telephone cables! ). Use large pieces of foam where possible, but where there is much curvature - bow etc. - you will need to use smaller pieces to prevent it cracking as it is bent. Take a lot of trouble over this, get it absolutely flush to the battens, and keep gaps between sections to an absolute minimum. At this stage you should put ply or high density foam pads in where any fittings will go - bow fitting, shroud plates, etc. Next you should fill all the gaps and fair off the foam. Use lots of very light filler as all this is adding unhelpful weight. Be careful fairing off the foam, it is very easy to sand away lots of foam and leave the filler standing proud ! All raised portions must be lost, but small shallow dents don't really matter too much. Once all the foam is in place, all gaps filled, and all is fair - check 3 times! - coat the foam with a mixture of resin and microballoons or litecell. The aim is to fill all the open cells on the surface with light filler, otherwise it will get filled with heavy resin when you put the glass on. The best tools to apply this are a one-foot plastic ruler or a piece of Formica with a straight edge.

The Outer Skin.

Apply the laminates next. Use a brush and a consolidating roller to ensure full impregnation - which can be a problem with Kevlar - and good resin to glass ratios. Remember you need enough resin to fully impregnate the fibre, but any more is just parasitic weight. Peel ply can be used and is very effective. Supposedly you can get a peel ply like nylon fabric from dressmakers which works nearly as well. I think I might be a bit wary of something like that in a vacuum bag lay-up though! A resin to glass ratio of 1.1-1.3:1 is achievable with polyester, and 1.8:1 with epoxy.

The Inner skin.

Once you have done this cut all the wire ties and turn the hull over. It will be very floppy (don't panic!) so support it in a good cradle. This can be used as the basis for a trailer when you've finished the boat. Put some extra reinforcement around where the centreboard case will come.

Space frames and bulkheads.

These can be made outside the boat and cut to shape and fitted later. Even if you don't have vacuum bagging you can (because they're flat) still compress them while they are curing. Do this with a couple of sheets of flat wood (chipboard is fine), covered with melinex - polythene may wrinkle. Put one piece on a flat floor, add your lay-up, and put the other sheet on top and weigh down with anything to hand - I used the last 5 years of Yachts and Yachting and Boards magazines. If you can't get melinex readily use Parcel tape - yes, the brown stuff! Epoxy won't stick to it so its great for these sorts of jobs. It can even be used instead of a release agent on moulds. You do - of course - have to be very careful not to get wrinkles and creases in the tape when you stick it down. Bulkheads can have one layer of 200g glass (or carbon) each side, but the space frame and high load points should have uni-directional carbon reinforcement under the glass. The bulkheads can be glued straight in with epoxy fillets, but the space frame should be glassed in to distribute the loads. It should hit your ply pads too! The exact layout of bulkheads depends on your fibre lay-up. A carbon boat needs less in the way of internal bulkheads. Below the floor a Glass boat will at least have a full length central spine, a bulkhead under the mast, one at the back of the daggerboard case at the mainsheet takeoff and one in the middle of the helmsman's stamping area. There's not normally a need for an extra bulkhead in front of the mast, but it is good to add some extra reinforcement as this area takes a pounding upwind in a chop.

Daggerboard case.

Use 55kg/m3 foam if you have it. Glass one side of the foam and allow to cure. Then bend each half of the case around the daggerboard and clamp in place. Don't forget the parcel tape/plastic sheet to stop it sticking. Glass around the outside, then remove the board and cut the case down leading and trailing edges. Coat the inside surface with a gel-coat type layer, preferably with graphite in, so that the fibres cannot get worn down. The two sides are then spaced apart a bit with foam or wood, and the whole lot glassed together again.

Decks and Interior.

Made in much the same as the bulkheads. You can use a jig - especially if you are making neat rolled side-decks, or use the bulkheads as a jig. Don't forget pads where fittings will go - jib sheets, cleats etc. etc. Get the parcel tape out again to hold the decks down! There are currently three interior layouts in use. Most common is still the traditional flat side-deck and side tanks with a slightly concave false floor. However there are also two variations on the “scooped deck from side to side theme. Andy Paterson builds his boats without side decks at all. The false floor comes up to the point where topside meets flare, and the crew sit on the inside of the outer skin. An alternative is to have a steeply raked in side deck which meets the false floor in the same way, but still having a side deck. If you are opting for the side deck less route you will have to have a substantial gunwhale structure to stiffen up the boat as you won't get the box section effect from the tanks. However in all cases there is a considerable advantage in having a gunwhale arrangement that leaves a lip under the topside. When you have capsized and inverted the boat you need to climb on top. This is lots easier if there's a nice lip at the edge to rest your feet on.

The False Floor and Finishing Touches

Use 75kg/m3 foam. This area is prone to dents (!). Glass on the bottom layer before you put it in the boat, using one layer of 200g/m3 glass. Put a fair bit of light resin/filler paste on top of the bulkheads and weigh it down (Y&Y again ?) until it is cured. Once it is firmly attached you can put the top layer of glass on. Use two layers of 200g/m3. Leaving the top layer off while you attach it leaves the floor more flexible while you fasten it down. Lastly run an extra layer of glass over the gunwale where hull and decks join, partly to keep the whole thing together, and also to give some abrasion resistance for rigging on concrete and to help protect against unplanned impacts from solid objects! Odd brackets for fittings etc can be jigged up on little moulds/jigs made from wood covered in parcel tape, but its easy to spend hours making little jigs to not much benefit. There's a lot of mileage in making up a largish bit of foam coated in glass each side and cutting things out of that. If you are compressing down small bits with jigs then, even if you don't use it for the big jobs, peel ply is recommended. It can make a big difference to how neat the bits come out and how much finishing work is needed, which is a big plus if its an awkward shaped bracket.

Fairing and smoothing

Absolutely crucial of course, not for strength but for boat speed. Use the lightest filler you can afford, mix it in resin, and spread it on as evenly as you can. A plastic ruler is very good for this. Once it is cured you can start sanding it all off again, the aim being to get down to a fraction of a millimetre above the top layer of cloth. In practice you are bound to end up sanding some cloth off, but make sure it is the very bare minimum. If you have a layer of Kevlar you must not expose it. Kevlar doesn't sand off - it leaves little fibres sticking out ! Different jobs on the boat need different fillers. Fillets and things need some colloidal silica for strength - a mix that is solely bubbles is very soft. For really high load applications, and especially in tension, microfibres are great, but they soak up a lot of resin and so get heavy. You can load up the resin with a great deal of filler - if you are simply filling with no need for strength then it can be almost “dry”. Be aware that these mixes are very soft though, so if the area needs dent resistance you will need to have some silica and a higher percentage of resin in the mix and accept the weight penalty. The lightest fillers are plastic bubbles - Fairlight or something similar, but are very soft. Microballoons - - the brown phenolic resin bubbles - are significantly stronger. For really serious filling you can make a brushable filler. Make up a reasonably thick filler mix - still a bit “sinking,” maybe 80% of maximum amount of filler you can mix in, and then add a little epoxy solvent - proportions perhaps 50cc resin, 250cc filler and 20cc of solvent and you have a brushable filler that will sand off readily. An adequate substitute for epoxy solvent - at least for cleaning and so on, is a general purpose industrial solvent of 90% methanol, 5% xylene 5% toluene.

Cost & Time.

It will take you in excess of 200 hours to build a hull once your jig has finished. Most people seem to take about 4 months to fit it all in including fitting out etc. Foam sandwich is a more expensive option than wood, but the final total will depend tremendously on materials. As of 2001 the materials cost is probably about UK£1200 for a glass/polyester boat, going up to UK£1750 for an epoxy/carbon hull. In the US it works out at around US$2600 for a predominantly carbon boat.

If you don't want to do the whole job yourself, whether through lack of time, skill, or inclination, an obvious alternative is to start with a part built shell. Quite a nice option is to buy a shell complete with false floor, which means that the trickier jobs are done.

Jim Champ.

This article was compiled in 1991 with the help of Dave Roe, Alistair Cope, Bill Deeley, Simon Baker and Simon Roberts, and updated slightly in 1998 and 2000 with help from numerous others, including Robin Russell, Matt Searle, Andy Paterson and David Lee. Especial thanks to Andy Paterson for teaching me about Parcel Tape!

If you wish to have fuller construction details for building a foam sandwich boat then it would be worth considering purchasing a set of plans from Bloodaxe Boats, which contain much more detail than is practical to include here.

Building Foils

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Building Foils

Disclaimer

This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. “Best practice” also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors and therefore may resort to litigation then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a foil without someone experienced in the materials to contact for advice.

The Shape

The planform and section shape of the foil can make a big difference to the drag and efficiency. The selection of this is dependent on the use to which the foil is intended i.e. rudder or centreboard for more ideas about the shape see foil_design.

The Core

The choice of core material will have a big impact on how you build your foil and will also affect the final weight. Traditionally foils were made from a solid wood core strong enough not to require any kind of skin to provide the stiffness and strength (this was often a hard wood such as Mahogany). However, by reducing the density of the core and adding a high strength/stiffness outer skin the weight of the foil can be reduced. With a modern foil the strength comes from the skins, and the core just acts to hold the thin skins in place, and transfer the shear forces from one skin to the other while resisting crushing.

Wooden Cores

The first steps away from the monolithic wood core was to use a low density but strong wood such as Western red Ceader. This can still be worthwhile as for a single project small quantities of wood may be more available than small quantities of high density foam, and many people find wood more pleasant to work with.

To build a Wooden foil prepare an even thickness blank from timber strips approx. 50mm wide. Quarter sawn strips are preferred as they are stronger. Organise the strips so that alternate ones are turned end for end the grain should run in different directions to reduce the warping of the timber. Warping can happen long after the foil is fully coated and complete, particularly if moisture gets into the foil through damage to the skins or pivot holes.

The timber strips should be bonded together with epoxy and clamped to a flat surface. When cured plane the blank to an even thickness. Cut out the profile of the blade, but make it 5mm smaller than the intended finished size at trailing edge. (Apart from anything else this ensures that minor damage doesn't expose a wood core) Shape the foil, allowing about 1.5mm undersized for the laminate, fairing and painting. Make the trailing edge as sharp as you can, because the fibres will overlap here to create the true trailing edge.

Plywood

Plywood is a medium to high density engineered wood product with the wood fibres alternating in direction by 90 degrees in each ply. Wood is significantly stronger along the length of the fibres than across them, however in plywood many of the wood fibres will be at 90 degrees to the load direction so will not contribute much to the strength or stiffness of the foil, yet will still be adding weight. Plywood has been used recently as the core for carbon skinned lifting foils for T-foil rudders, where the small size and thin sections make the core difficult to shape out of foam, and crush resistance is important. As only a small quantity of the plywood is used it's high density is not such a problem, and the main strength comes from the carbon skins.

Foam Core

The best core material is probably high density PVC foam (200 kg/m³). If you're really keen the core can be done with two different densities of foam using 80kg/m3 near the bottom. Failing that you can use 80kg/m3 foam but with a spar made from wood or high density foam to spread the compression loads into the blade. It is also possible to create a carbon web joining the skins together, or rout several grooves in the core, and fill these with UD carbon to provide support to the skins. If you are using an engineered core it is important to taper the high density part to avoid point loads at the end. Lower density core is quite flexible and delicate so it can become difficult to shape on thinner sections particularly close to the trailing edge.

One of the most common failure modes with light weight foam foils is for the core to crush against the sharp bottom edge of the boat, this takes the skin on the compression side out of column and quickly leads to a broken foil, which is the reason for using either the higher density core, or dual density core.

Foam is typically sold in quite large sheets, of different densities, and thickness. It is generally possible to get a sheet of the required thickness, sufficient to make several foils. However if this is not cost effective, you can bond two thinner sheets together. The foam resists shear forces from one side of the foil to the other so if using two thin sheets the bonding between the layers is important for the final strength of the foil.

Shaping the Foil

The shape of the core will determine the final shape of the foil so getting this right is an important first step. It is also important to remember when shaping the foil that the laminate will add around 1-2mm to the thickness of the foil shape, and that the skin will need to protrude several mm past the end of the foam, or wood to allow for a solid trailing edge.

There are a few techniques used to judge the shape while you are removing material.

Templates

Templates of the final shape are made from wood or other stable material, if there is significant taper on the planform then extra templates are required for the smaller sections. These templates need to be smaller than the final shape by the thickness of the laminate. The Centreline is marked on the blank, once the shaping is complete the template should match up against it. Initially material can be removed quickly using a belt sander as you get closer to the shape a flexible long board can be used to avoid dimples and hollows. You should check regularly with the template to ensure that you are removing the correct amount of material.

Hot Wire

Commonly used for making model aeroplane wings a polystyrene block can be shaped by cutting with a hot wire. The wire is held under tension using a bow, it is heated by passing a current through it from a battery (this needs careful control to avoid melting or softening the wire). The bow is drawn across a template fastened to each end of the blank to cut out the shape of the foil. If the wire is not tight enough it can move away from a straight line causing a hump, or hollow in the middle of the foil. This technique can only be used for a parallel or straight taper foil, although you could hand shape a more complex tip shape after cutting. Polystyrene foam is very low density so a foil built from it will need either a spine, or additional reinforcement to prevent crushing, just using a thicker laminate may not be sufficient.

Routing Contours

A router can be used to cut grooves along the length of the blank at the required depth for the position along the chord. The contours for each depth are marked onto the foil, and groves cut with the router following the appropriate contour. When sanding it is easy to see if you are approaching the required depth as the grooves will start to disappear. Once the core is rough sanded the final sanding should be done with a flexible long board to avoid bumps and hollows.

CNC Machining

The shape of the foil can be designed in a 3D cad program which is then sent to a workshop where it is used to program a CNC milling machine that cuts the shape out, a step distance of 1mm is typical. A higher density foam is often used for this as it needs to remain stable during the milling process. A light sand will be needed to remove the ridges from the milling process before the foam blank is ready for laminating. This is probably going to be the quickest option, and for a complex shape may give a more accurate blank, however that will depend on the design, and on the accuracy of the machining. To get an accurate shape the blank needs to be held solidly. If you mill the foam away to a thin edge, then it is likely that the blank will distort under the cutting head, ruining the shape. Small concave shapes are also hard to cut due to the shape of the cutting head. For this reason CNC machines may be more suited to making plugs, or moulds, rather than the finished foam core.

In a Mould

It is also possible to build a foil in a mould, this is typically done with two half shape moulds for the skins, these are then bonded together around a roughly shaped core. There is a large time investment required to build the moulds so this technique is good for building a large number of foils of the same shape, rather than prototyping a new shape. Particular care needs to be paid to the join between the two half skins to avoid splitting. An internal flange could be used, packing could be used on the leading edge to allow you to laminate a strip of cloth on the outside of the blade, and then fair it in. If the foil is built in a mould then expanding epoxy foam can be used to form the core of the blade. There have been some L shaped T-foil rudder moulds made, these use two different Ls for the rudder and top surface of the lifting foil, and a separate flat mould for the lower surface of the lifting foil. This allows you to make the joint smaller, which should reduce drag.

The Layup.

Skins of unidirectional carbon and woven carbon cloth, will give lowest weight and maximum stiffness. Start with layers of 200 g/m² unidirectional carbon, one layer over all of the foil, plus a second layer of 200 g/m² unidirectional carbon over the top half, and a third layer of unidirectional carbon, approx.150mm wide, over top part of the foil, extending approx.100mm past the bottom of hull when the foil is right down. Then add one layer of 200 g/m² woven carbon cloth, and finally a layer of 86 g/m² glass cloth, both covering all of the foil. If you wish you can use white pigment in the top layer to enable you to produce a white foil without painting it.

Laminating it

It is often a good idea to skim the board with a mix of micro-balloons and resin to fill the broken cells in the foam with a lighter mix than pure resin, it can also help to get good adhesion between the skin and the core. Suspend the blank with the leading edge horizontal by means of screws in timber supports at the head and tip of the board. Cut the carbon oversize, approx. 50mm wider than the board. Using a roller, wet out the board with resin, apply the UD carbon, aligning the fibres along the leading edge. Wet out the fibres with epoxy, leave a few minutes to soak in and then wet again. Next comes the layer of carbon cloth. Again wet it out off the foil, wait a few minutes, and the roll on more resin. Finally add the layer of glass in the same way. Squeegee the excess resin away, remove air from the laminate, then squeeze along the trailing edge overlap to remove air. Check for bubbles under the glass, and squeegee out.

After approx. 1 hour it’s time to add filled epoxy which will be used to fair the foil. Make up a reasonably runny filled epoxy mix that will roll on nicely. If you're going for a pigmented foil then use glass bubbles and white pigment. If you're going to paint it anyway leave out the white pigment, and if you have ambitions for a clear finished foil (your laminating better have been really neat if you're attempting this) use silica in place of glass bubbles. Anyway roll on a coat of filled epoxy and repeat twice more ( 3 coats resin/glass bubbles). When the layup is part cured (still a little flexible, but no more than that) trim the excess glass from the head and tip with a sharp knife. Leave the foil to cure overnight

Remove the supports and screws, and trim the trailing edge to the finished size, using a jigsaw with a carbide tipped blade. Trim and sand the head and tip areas. Now it’s time to glass coat them. Apply 2 layers x 200g/m² glass to the head edge, and 3 x 200 g/m² cut on bias at ±45° around the tip of the foil. Cure overnight.

File / sand all the edges to shape. Apply 2 coats of resin/glass bubbles to the head and tip. Cure overnight, and then the next day post cure the foil at approx. 45°C for 3-4 hours (A wooden box & a fan heater does this nicely).

Vac Bagging

If you have the facilities to vacuum bag your foil then this can help to consolidate the laminate and remove excess resin, see the Vac Bag how-to for more information.

Finish

Now the hard work begins! Start by spraying on a guide coat ( car paint ) of some contrasting colour with the layup (bright red perhaps). Sand all the paint off! You should have enough filler to sand pretty aggressively (Andy Paterson uses a belt sander with 40 grit abrasive) without cutting (much) into the glass. On no account whatsoever cut through the glass, and cut into it as little as you possibly can. If it goes black stop immediately!

Now suspend the foil with the screws and blocks as before, leading edge up. Finish the foil with 2 coats of neat epoxy (with white pigment if appropriate. Leave the first layer to cure for approx. 1 hour, then a 2nd coat. The epoxy will fill and flow over the big scratches. When this has cured fill suspension holes, and apply 2 coats of epoxy on the head edge. Apply another guide coat of paint and sand, sand, sand, the finish coats. Wet sand it starting with 100 grit, working through 180/280/400 and then finish off with 600 wet sanded to give smooth matt finish. Most people think this is all the finish required, but feel free to carry on with 800 grit and 1200 grit and then an abrasive polish to get a real mirror finish. It will last at least a day on the beach!

Handicaps of Cherubs through the ages

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Handicaps of Cherubs through the ages

These figures are suggested by the Class Association for those racing older boats. They are calculated from old Portsmouth Yardstick numbers for the class at various times, taking into account significant rule and design developments.

UK PY no.	Classification	Distinguishing Features
920	2005	15.5sqm upwind area + 21 sqm Spinnaker.
975	1997	Hull after 2672 with 12.5 sqm upwind area and 15sqm spinnaker.
1000	Converted to 97	Hull meets 1990 rule with snout and/or 1.8m beam with “unfair” gunwale plan with 12.5m2 upwind and 15m2 spinnaker
1050	1990	Hull after 2635 or 12.5m2 rig, no snout and 5ft beam at mid length.
1080	1984	Hull after 2550 or 125 sq. ft. rig.
1100	2400	Hull after 2400 and 110 sq. ft. rig
1115	1900	Hull after 1900, 110 sq. ft rig 120 sq. ft.conventional spinnaker.
1140	Veteran	Must have hull before 1900, 110 sq. ft rig,triangular or no spinnaker.

* The RYA has published the handicap list for 2013, which can be downloaded here the Cherub has been given an experimental number of 920. This number is experimental because of a reduced number of returns.

If you have any questions then please feel free to contact the class for answers.

Note: 2705 Flat Stanley has a New Zealand sail number and should be considered to have a hull equivalent to UK number of 2550

How-To Articles

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

How-To Articles

How-To Videos

Vacuum bagging video. (Quicktime needed)
Mast building video (part 1). (Quicktime needed)
Foil building video (part 1). (Quicktime needed)
Spreader building video. (Quicktime needed)
Hull repair video. (Quicktime needed)

Repair Techniques

Building Carbon Masts

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Building Carbon Masts

I never managed to get anyone to write this for me, so, as I was acting as an amateur journalist, I thought a journalists trick would do. I sat Simon Roberts and Dave Roe down with a pint each, turned a tape recorder on, and asked stupid questions. Some might also consider it characteristic that Simon ended up buying the pints because I didn't have enough cash on me.
Jim Champ

Mast Building Movie
Spreader Building Movie (coming)

Disclaimer

This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. “Best practice” also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a composite structure without someone experienced in the materials to contact for advice.

Introduction

Mast building is probably the most challenging laminating job the amateur boat builder is likely to take on. It means handling a lot of material in a particularly tricky lay-up, and the consequences of getting it wrong are serious. If you build part of your boat with an unnecessarily strong lay-up then you've wasted a little bit of material and added a few grams of unnecessary weight, and if you make it too light then there'll be a small loss in stiffness and possibly the need to reinforce it. The kind of lay-ups described in other sections of these articles are very much on a “that will be plenty strong enough and adequately light” basis. Masts are more difficult. OK the possibility of making it badly and it ending up breaking is there, but that.s not the major issue. What's more serious is that the actual stiffness on the mast has - of course - a huge effect on the performance, and the actual difference between what we'd regard as a stiff mast and a bendy one is not really very much. This means that's its reasonably easy to end up with a telegraph pole or a fishing rod… Don't take on a mast until you've done a good lot of laminating and can consider yourself reasonable skilled. You're also well advised to do a boom or a bowsprit first because the much smaller size makes the project easier, there's less of a worry about it ending up too stiff, and in any case its not such a big lump of cash in the bin if you get it very badly wrong. This article is also rather less of a “how-to” than the others in the series, and rather more of a “how we did it”. The folk who are building masts within the UK fleet are doing it with the benefit of some years experience and several boats behind them. There's no substitute for “getting your hands sticky”. Its also well worth pointing out that there's no consensus as to the best way of building masts yet, and there are other methods that work just as well - maybe better.

Designing the Section.

Its possible to start with a theoretical list of stiffness values and so on, and then go from there. This is what the companies who build big one off yacht masts and so on must do. All any of us have done is to start from a know alloy mast with published data as a basepoint, and then say - well, a bit stiffer sideways, much the same fore and aft, bendier at the top and so on. Working out the values for mast taper is mostly informed guesswork as the figures are not published, and although we have tried to measure one, we didn't really get any results that we had too much confidence in. Designing the section isn't about the cross sectional shape itself, so much as identifying the dimensions and fibre lay-up that will give you the stiffness you want. The maths is roughly Mechanical Engineering graduate student level, which may not daunt you, but rather does me. If you have access to reliable information that other people have worked out then all well and good. Basically a carbon mast tends to consist of a substantial layer of unidirectional fibres sandwiched between two layers of woven carbon which are primarily there to keep the unidirectional carbon in column and prevent buckling and peeling. There are two ways of going about working out what this this lay-up should be. One is to start with an existing mandrel or mould and then work out what lay-up is going to give you the stiffness you want. The other alternative is to work out what lay-up you want to use, and then build a mandrel or mould to give you a section that will do the job you want. For instance Dave Roe's 1997 mast was based on 4 layers of unidirectional fibre. The actual mathematics required to design the lay-up is beyond the scope of an article like this - suffice to say if you haven't got either the mathematical skills or access to someone who has, or access to the technical information on the materials you propose to use, then probably you shouldn't be getting into mast building at the present state of the art As an example one starts with the stiffness value of the particular carbon that you intend to use for the main structure of the mast, take off an allowance for the amount of resin that is likely to be in the lay-up, add allowances for internal and external skins (usually an order of magnitude smaller than the main unidirectional fibres), add an allowance for the mast track and then see what sort of figure you arrive at. This result may be unsatisfactory for one reason or another, in which case you have to repeat the exercise until you get something appropriate. A particular consideration here - especially with dinghy masts - is that they get bashed about a fair bit, what with beaches and trailers and roof racks and so on. Its probably fair to say that anything with a wall thickness of less than 1.5mm will be too prone too damage when not in use, no matter how appropriate the structure is for sailing with. A couple of rules of thumb that can be of use are:- Carbon rigs tend to be at least 20% stiffer than the equivalent section in alloy. This means that you can usually go one section size down when basing a carbon rig on an existing alloy one. A 200g carbon cloth makes for about 0.2mm of section thickness in a lay-up.

Material

You must be using a low viscosity resin with a very long cure time. It will take you hours to laminate up the tube. Resins from the Ampreg range are the conventional choice - Ampreg 26 is good. There are several reasons for using the Ampregs, which are, on the face of it, very expensive, but basically it boils down to “you get what you pay for” and in the case of the Ampregs you get an easy to handle lower toxicity resin with lots of desirable properties like low heat sensitivity, especially when cured. Don't economise on resin. Especially, whatever you do, don't consider using polyester resin! There are all sorts of nasty small scale phenomena that can occur in carbon masts which just aren't an issue in a relatively low stressed hull construction that can cause all sorts of problems. One of the worst is “microcracking” which occurs if the resin takes up load before the carbon and cracks. Suddenly the carbon is unsupported and… I'm sure you can guess what happens next. In the UK we tend to use fairly ordinary grades of carbon, which seem quite adequate. For the woven cloth inside and out we use a single layer of 200gsm carbon, which is the most economical currently available. Two layers of 100gsm carbon, aligned in different directions would be superior, but four or five times the cost. Higher grades or carbon could certainly reduce the size and weight - Dave Roe has calculated that he could make a 1.5 inch diameter mast that would be around 70% of the weight of the current ones, but that the material cost would be something like three times greater…

Laying it Up

Release Agent

In the past we've used a lot of paraffin wax as a mould release agent that can be melted out. If you have appropriate facilities and are using an aluminium mandrel then laminating and curing at a relatively high temperature can help considerably as the thermal expansion of aluminium exceeds that of carbon lay-ups. Experience seems to indicate that ordinary mould release agents just won't guarantee you to be able to get the mast off the mandrel. One method that has had some sucsess is to cover the mandrel in candle wax this is melted in a pot and brushed onto the mandrel, and smmothed with a low temperature iron. When the time comes to get the mast off you can heat the mandrel by blowing steam through it a walpaper stripper is a handy tool. Once the wax is soft the mast should slip of eaisily.

Consolidation

Lay-up consolidation is absolutely essential. The best bet seems to be vacuum bagging. There are people who use tape successfully, but there are a number of dangers in this, most especially that of dragging the lay-up round the mast in a spiral which will probably result in less stiffness than was planned. I don't propose to go into a full treatment of vacuum bagging for the amateur here, but there's space for a few pointers. Supposedly there are some good books on the subject, but we've all learnt from talking to people. There's a lot of people who use the techniques in one industry or another these days, at least in our part of the world. Peel ply is essential. Perforated release film is good, but hopefully the peel ply will soak up the resin unless you've got far too much in the lay-up anyway. Breather cloth is quite cheap, and you may as well use the real thing, even though some people use Chopped strand mat instead (about all its good for!). Even old blankets from a car boot sale will do the job at a pinch though, and are much better than nothing. You can use virtually any airtight sheet plastic for bag film but proper bag film is very thin which leads to smaller wrinkles, a better finish and less extra work. You will need to smooth the bag down as the vacuum goes in to minimise the wrinkles. Where the vacuum goes in is important - in practice bags always leak, and so if you have a leak near the inlet you may not get much vacuum at the other end. A tube with holes in to distribute the vacuum is thus a very good idea to equalise things out. SP recommend no more than 0.5 bar for the vacuum but by the time you've spent 4 hours laminating it up so the first layer is half set, you're working maybe in 16 degrees instead of the specified 21 then you may need to go higher simply because the viscosity is higher and the mix has half gone off as well. In practice if all the bleed cloth is saturated in epoxy you won't get much more resin out of the mix, and if you've put 4 layers of unidirectional on that's about right. The danger with more tractable lay-ups is that you can actually suck so much resin out of the cloth that the strength is badly compromised Having said that the lower the resin ratio the better (well almost) and carbon masts need to be as dry as you dare go. At a maximum you should be looking at a lay-up that is one gram of resin for every two grams of fibre. If you're not confident about achieving that then maybe you want to tackle another boat before you do a mast. Unidirectional cloth that has glass binder is useful for helping you see how well wetted out the lay-up is. Its also worth noting that the consolidation effect of the vacuum increases exponentially with the decrease in pressure, and at the far end small improvements can lead to big changes.

Inner Layer

The technique we've used is to lay the mast up around a mandrel - effectively a male mould - and vacuum bag the mast onto that. Others have apparently made spars by making a female mould and using a bag on the inside to consolidate the lay-up. I guess that this would be more work on the mould, and more trouble to lay up, but be considerably easier to remove mast from mould. The first (inmost) layer of lay-up is local reinforcement where fittings and so on will go. This is usually plain glass, and then a layer of light kevlar. This has two roles. The first is to add local strength where fittings and so on penetrate the mast, and the second is that the glass insulates the electrochemically active carbon from the fittings. Kevlar is chosen because its excellent for resisting crack propagation and so on, but has a tendency to go “furry at the edges”, which glass doesn't suffer from. The next layer should be Carbon cloth, 45/45 degree aligned for torsional strength. This is adequate for a dinghy mast, but something bigger will need to be designed more carefully. Its worth noting that, in contrast to a metal mast, fibre masts are not made out of a homogenous material, and can and will have significantly different properties according to the alignment of the fibres. It is not especially easy getting the fibres properly aligned and can be wasteful of cloth. None of this job is easy!

The Main Fibres

Once these layers have been cured and tidied up the main lay-up of uni-directional fibre can be commenced. This needs to be done as a single job, which will take several hours. Obviously it needs to be done carefully, making sure that all the fibre is properly wetted out (not always easy to tell with carbon,) and that there are no voids and that the fibres are correctly distributed round the spar. Fair up this layer before you put the outer skin on. Here you've got to be careful with the (virtually inevitable) wrinkles. If you have longitudinal wrinkles of carbon sticking out then you can sand them down without too much worry. After all what they principally represent is fibres that have been squeezed out as the laminate compresses down, so you can take them out without compromising strength or lay-up thickness. Horizontal wrinkles are trouble because if you sand them off you are breaking into the carbon at a single point, making a spectacular weak point. This is mainly a matter for very careful vacuum bagging.

Mast Track

The track - provided you aren't making a trackless mast for a sleeve luff rig - should be made from half inch diameter pultruded tube from whatever your handiest source is. Glass is cheaper, heavier, and has less impact on the final bend characteristics. Carbon is more expensive, lighter, and contributes more to stiffness, especially fore and aft. Glue the track on with a reasonably strong filled epoxy mix, and then fair up the gap between tube and mast to your preferred shape with something a bit lighter. In New Zealand they take a different approach. They make their tracks from a rubber type caravan awning track which bends very easily but does not seem to lose the bolt rope out of it. This is glued onto the mast using a particularly flexible adhesive called Sikaflex. Take a good look at the end of the mast track where the sail feeds in. Its very easy to let the luff rope get trapped across the groove. This puts a very big load on the track and has bee known to actually crack the track, after which the luff rope gets in the slot more and more often, rigging is a pain, and the luff rope can pull out of the groove whilst sailing.. Rainforce the last inch of the track so that this doesn't happen. Similarly be very careful about the end of the slot. If its too sharp a corner you may risk tearing the sail, but a very even taper means the luff rope getting caught for sure.

Outer skin

Lastly on goes an outside layer of 200gsm carbon, this time aligned 0/90 degrees to the mast, plus appropriate local reinforcement where needed. It goes round the mast track of course. Should you ever wish to modify the stiffness of the mast by adding (not always successful without great care) or removing fibre, you should sand off this entire layer and then replace it when you've made the changes. One has to be very careful about adding extra fibres later, because its very difficult to get really first class bonding between the original and added structure, which means that there's always the possibility that the load won't be distributed between the fibres that well. There is no especial constructional reason for having the 45/45 layer on the inside and the 0/90 layer on the outside other than it is easier to make a neat job of the 0/90 lay-up. As mentioned above the optimum would be a thinner layer of both each side of the uni-directionals.

Getting it off and Putting the Fittings on.

A lot of people commercially are working on reliable release and easy lamination. It can be big trouble. Quite often its easier to simply cut the mast down one side and take it off like that. After you do that you'll need an outer layer of carbon again, but its not as disastrous as you might think because your cut is aligned with the majority of the fibres anyway. If you have an alloy mandrel you can make it as cool as possible to shrink it out from the lay-up, if you used wax then very hot water down the centre of an alloy mandrel gets it out a treat, or alternatively you can melt it out with a heat gun (don't get the lay-up too hot!).

Cut out the slot in the mast track. I suppose in theory the slot reduces the effect of the outer layer of fibres, but the track itself contributes plenty of strength in that area, and it doesn't seem to be a problem. Fit out the mast out pretty much as normal - but be *very sure* that the fittings have been placed where the reinforcement for them was. Corrosion is a significant consideration - carbon is electrolytically active and there's a considerable potential between it and aluminium. Make sure there's no contact between aluminium and carbon - stainless rivets are definitely preferred. This applies to other fittings as well. Again glass can be used as an insulator, but resin coat the alloy fittings too and generally do your best to keep them isolated. In this context its worth noting that I've heard reports that RS600 mast bottom sections - which have an aluminium sleeve to shorten the mast to reduce sail area - have, in some circumstances, actually failed because of the expansion caused by corrosion of the aluminium. Be very careful with rivets and avoid them if you can. In particular make sure that the holes you drill for rivets are as tight as possible in order to avoid the rivet expanding in the hole and causing a local distortion in the structure. For similar reasons backing washers on rivets are nothing but a good thing if you can possibly get them on. Finally paint it. The main reason for painting the tube is to provide UV protection. This most especially applies to a mast, which unlike the boat tends to be out in all weathers uncovered - at least if your boat lives at the Club all year round. For this reason I painted my carbon mast white, as this should reduce the amount the layup gets cooked on hot days. Having said that all the mass production companies seem to think a clear lacquer to stop the UV is more than enough, and if, like many Cherubs, your boat lives in the garage, not the sailing club then its not nearly such an issue, so paint it all the rainbow colours you like!

Spreaders

The Spreaders are a very important part of your rig, they help to control mast bend and to hold the mast in column so it is important to get them both in the right place and strong enough to cope with being bashed off the ground a few times while rigging. The eisiest way to make a spreader is to start with a foam core shaped to fit the mast and taper towards the tip. This is then tacked into position on the mast and the carbon is added to give the strength.

Primal gets a new spinniker chute

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:21:59 +0000

Primal gets a new spinniker chute

The Problem

After a bit of time spend sailing Primal we decided that there was a problem with the geometry of the spinniker chute. The old version was very low and did not give much space for the kite to squeeze through. There was also a sharp corner between the chute and the side of the boat which meant that if the kite got dragged back it would jam in the corner. Winter gave me the opertunity to come up with a new design to avoid these problems.

The Design

I wanted the mouth to be as rounded as possible with no sharp corners and a relitavly large diameter that would let the spiniker slip into the chute. I was inspired by the story from the Dinghy show of a Mirror with a chute molded around a bicycle inner tube. So decided to give it a go. I built a jig to match the shape of the bow of the boat that I could sit the partially inflated tube in while it cured. I covered the inner tube in parcel tape so that it would release and then put on a single layer of glass and wrapped in peel ply. With the inner tube pumped up a bit more I put it all into the jig to get the shape right and left to cure.

Construction

Once it had cured I could pull the inner tube out and it was almost ready to fit to the boat. The old one was cut out and the paint sanded back to a clean surface to bond on to. The idea was to sit the new chute on top of the gunwale as this would give more space for the spinniker and would give a slight increase in freeboard to try and keep some water out of the boat. The tube was tacked in place with hot glue and some bits of foam cut out and used to support it and to provide an end to the tubes. With all the foam in place the whole thing was covered in Carbon and glassto attach it and build up the tube from the initial single layer of glass. Peel ply was used to keep it all snug while it cured.

Finishing

The whole thing was filled, faired and painted. Ready for attaching the sock and the jib sheet.

Did it work?

First impressions are good the kite seems to slip in and out of the new chute much eisier than before and a trawling sesion does not mean a trip to the foredeck anymore.

Click on the pictures to enlarge

Back to Primal Scream

Fitting Out and Handling Pole Kites

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Fitting Out and Handling Pole Kites

By Jim Champ There seem to be quite a few folk restoring old Cherubs these days, so I thought this would be useful.

Rudyard Kipling wrote “There are nine and sixty ways of constructing tribal lays, And every single one of them is right!” Much the same applies to Cherub Spinnaker systems. What you're going to get offered here is substantially what I have on my vintage boat Queenie SJB, somewhat crossed with what I used on Halo, my Bistro, which was the very last Cherub to be built in the UK with a pole kite system.

Spinnaker Pole.

This needs to be nine feet long and very substantial. Superspars used to do one that was basically two two/thirds of 505 poles sleeved together to make the extra length. I'm sure they could make one for you if you need one. There were also some really bullet proof ones made from two Needlepar topmasts sleeved together. I imagine either company could make one to order in the same manner. Even so the sleeving was sometimes prone to bend, as indeed it has on my Superspar.

I prefer, and writing this now advise a double ended system. I still think single ended systems are easier for beginners at Cherubs, but I'm finding that without other people to learn the tips and wrinkles folk who are just getting into sailing a pole kite Cherub have a lot of trouble setting it up. You tend to need a stronger pole for double ended systems though, but almost everyone used to break at least one until they got one of the good ones as noted above.

End fittings on the pole need to be very good. Ideally you should be able to just push the pole on from both top and front. I like the Ronstan RF2569, but I have broken them too. You need a reasonably substantial trip line between the two end fittings to release them remotely, not just thin twine. In the middle I use a keyhole system, with just a bullseye fairlead. A solid fitting for the keyhole is best, something similar to a RWO R4282, but just a rope loop works OK for me for casual sailing. Whether you have a rope loop or a keyhole fitting it needs to go inside the trip line, because the trip line also serves to keep the uphaul/downhaul on the pole and indeed the pole attached to the boat.

The mast fitting must be stainless steel and strong. Plastic ones will bend and break. Locate it exactly opposite the gooseneck fitting, not higher up like most boats. If you put the fitting high up on the mast the compression loads from the pole will put an S-bend in the mast, which not only turns the mainsail a horrible shape but also trebles the risk of losing the mast in a pitchpole! Down at the gooseneck its stabilised by the lower shrouds (you must have lower shrouds!) and the rig works much better.

Halyard

The spinnaker halyard is the only one you really need in a Cherub. It needs to be as low friction as possible, which really means a thin rope. Sorry! With no other halyards in the mast you know it won't get tangled up. The hoist height depends on the shape of your sail, but I think we used to set them too high. With asymmettrics we've learned that there isn't that much difference in having the sail closer to the water, especially as you get less heeling moment with the sail lower. Basically the halyard needs to be high enough that the sail doesn't drag in the water when the wind drops - about luff length above the deck is probably about right.

Downhaul/Uphaul.

This is where you get most variation. I now prefer the downhaul to come back to as close to the mast as possible, and use vectran or something similarly low stretch. It needs to have a two to one purchase to a cleat on the back of the daggerboard case where the helm can lean down and adjust it. The uphaul should go well up the mast - about the spreaders is good. A height adjustment on the mast is useful, but not essential. I don't bother now. It doesn't need a purchase because you won't often adjust it sailing. People used to use all sorts of arrangements with shockcord and so on to pull the pole forward, but with a bit of practice you really don't need to bother. I've even stopped using some elastic to take up the slack on the downhaul when the pole is stored, although its not a bad idea.

Sheets.

The sheet must be very low stretch. Buy good ones. If the guy stretches on a tight reach and the pole goes round the forestay it will break. With four feet or so of pole beyond the forestay it has lots of leverage.

The sheets should go round a turning block about halfway down the cockpit. Usually opposite the mainsheet between helm and crew. From there I always found the best layout was to run them forward along the topsides, through a block in the topside face and with a cleat inside. This is impossible unless you have either short sidetanks or else a special cut out in the sidetank for the sheet - a feature you'll see on a lot of 1980s boats. If you can't run it forward through the topsides it needs to be run to somewhere where you can put another turning block and a cleat. The cleat is a pretty much essential on a pole kite system because you have to adjust the guy as well, and because the sheets are more likely to be washed over the side - or worse still down the bow and under the stem.

Guy.

You need a reaching hook (Ronstan RF91, accept no weaker substitute!) as far forward as you can readily reach - probably level with the mast. You also need a cleat there, positioned so that you can cleat the guy on or off the trapeze. These are the highest loaded fittings on the entire boat and need to be spectacularly strong. Plastic will disintegrate. You will probably want a sheet catcher on the stem, because its even easier to lose the sheets without a bowsprit to catch them. Rubber hose in a loop screwed each side works nicely.

Pole Stowage

The pole is always stored on the boom. To make a bracket to support it get a piece of sailbatten or something similar about a foot long. Drill a hole in each end, aand then screw it to the boom in the middle so it sticks out each side. Tie a piece of line from the hole in each end up to the special eye on the mainsail you always wondered about (if the sail was cut by a Cherub sailmaker) or failing that to the bottom batten pocket. When you stow the pole you slide it along the sail through the rope loop and it rests on the sail batten.

At the front end you can have a couple of stainless eyes like the one on the mast, or else a little loop of rope. Either way you put the pole end fitting in this to keep the pole stowed neatly.

The Hoist

Get the boat on a very broad reach, but not quite a run. Put the pole out first. Hook the guy on the pole and push it out, taking the sheet with you. Have the guy in the reaching hook and cleated at the “not quite touching the forestay” mark that you absolutely must have on the guy. Once you have the pole well on the way to clipped on the helm can start pulling up the halyard, but you must get the pole on before the sail is halfway up. If it fills before you get the pole on then you won't get the pole on! You'll find that if you push the pole right out to the tack when you hoist it will stay there, there's no need to hook it up to the sail or anything like that. Hook on the trapeze as soon as you've got the kite up ready to fill, and point up very gently - the power and apparent wind will come rushing in and if you aren't careful you'll get blown over.

The Reaches

Once the sail is up handling isn't that different from the crews point of view, but this is a Cherub. You will have loads of apparent wind and inb a breeze you will normally sail all reaches with the pole two inches from the jib luff. The helm should sail the boat as they would for an asymmetric class, the techniques are all the same. All the books will tell you that its a good idea to keep the luff and leech the same height. This isn't true in a Cherub - the pole is so long compared to the foot that when set on a reach the clew will be appreciably lower than the tack, so forget about that!

The Run.

In a serious breeze you will probably want to gybe downwind like an asymmetric boat. Pull the pole back a moderate amount from the forestay - say about 30 degrees and pick your point for the gybe. Running dead downwind in a breeze, even with the kite, is not a great experience. Light winds are the only time when you sail the boat like any other conventional kite boat, except that with the long pole you can get an incredible amount of kite out from behind the jib.

The Gybe.

Frankly this is why we changed to bowsprit kites. See this picture! Get off the trapeze onto the fastest reach you can still keep the boat flat on, cleat the current guy with the sheet cleat and the pole fairly well aft, and unclip it from the reaching hook. Go into the gybe fast with as much speed as possible, get the boom across as soon as possible, but gybe onto a very broad reach. Clip the new guy in the reaching hook and cleat at the mark, get forward, take the pole off the mast, trip the old guy with the line, switch the rope loop/keyhole fitting on the downhaul to the other side of the fairlead, put the new guy into the end fitting and push the pole out again. Avoid pitchpoling while doing this (the helm may have to be hanging off the transom). Power the boat up gently (apparent wind will come rushing in) get out on the wire, and congratulate yourself on completing what was probably the most difficult manouver in dinghy sailing prior to the introduction of the Axeman narrow Moths!

You may do a bit of swimming while you get used to this. We all did! There is more on this in the downwind section of the heavy weather sailing article. Basically it comes down to picking your moment for the gybe, getting into the gybe with enough speed on, and not coming out of it too fast or too high.

The Drop

Power down as for a gybe and its usually easier if the helm pulls the retrieve in. When its about half way down the crew gets the pole off the mast and stows. Leave the sheet in the pole fitting until the pole is on the boom, it reduces the risk of dropping it over the bow. Tidy up the sheets as quickly as possible and head upwind again.

People's Projects

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

People's Projects

A bunch of photos of various people's boats under construction/alteration

Rig Set-up - Getting it Straight

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Rig Set-up - Getting it Straight

Probably as important as the configuration and number of shrouds that you have the basic set-up of your mast and rig if that is not right then the boat probably won’t point and will be more difficult to sail. The first stage is to get the mast set up so that it is straight in the boat and has no small sideways kinks or bends in it.

Getting it Straight

With the mast off the boat check the spreaders making sure they are of equal length and equal angles. The spreaders must be solidly attached to the mast. If they move under rig tension then it will be impossible to control what happens to the mast on the water and it is a good sign that they are about to break.

First sight along the mast to get an idea of how straight it is off the boat and how much it bends under its own weight. Next put the mast on the boat and pull on rig tension. When you sight along the mast it should still look straight. However you will probably see several small bends located at the spreaders and possibly the hounds. If you have a full set of lowers, D2's main shrouds and caps there could be several bends going on and it can be difficult to work out what is causing what and where to begin fixing it. Start by simplifying the whole thing drop the tension back off and disconnect all but the main shrouds and tension up again. There is likely to be just one bend now centred at the main spreaders check the angles and adjust the lengths slightly to take that bend out. It is worthwhile at this point to check if the mast is straight in the boat. So take a line from the tip of the mast and place it against the back corner of the hull (Best done on the chine as this is the part you need to be symmetrical to and not the top of the transom which may not be straight itself). Adjust the shroud lengths so that the distance is the same to each of the corners. Many Older boats had hog stepped masts with a mast gate at foredeck level this gate should be packed so that the mast is a tight fit side to side and the gate is not causing any bends.

With the mast in the right place it is now time to reattach the lowers and adjust the lengths so the bottom section is still straight with tension on the same needs to be done with the D2's if fitted. Finally we can sort out the cap shrouds these are the most difficult to do. As a difference in shroud length will bend the tip of the mast and a difference in the length of the spreaders will try to bend the mast at the hounds (which is normally held in position by the main shrouds). This will also result in the tip bending to one side or the other when the mast is in the boat. Depending on the set up it may be best to do this with the mast off the boat and just the cap shrouds under tension. First check the lengths of the wire disconnect them from the spreaders and pull down at the ends of each one they should be exactly the same length. Next fit them back to the spreaders and do the same exercise when you hold the ends together they should still be the same length if not then the problem is with the spreaders. With that all sorted out the caps can be tensioned back up again and care must be taken to keep them exactly the same length and sighting along the mast looking for bends is the best way of seeing that.

Rig Tension

With the verity of rig set-ups and configurations on Cherubs it is difficult to say what sort of rig tension should be used. In general the older and more delicate a boat and mast is it is safer to use lower tensions. If you are planning to increase the tension you are using it should be done in carefully in stages being aware of any unusual creaks or groans as you pull the rig on. Checking regularly for any damage to the hull or mast. The important thing to remember when changing the rig tension is that the length of the shrouds set the tension and the forestay sets the rake. This is because the fore and aft distance between the mast and the shrouds is tiny compared to the distance between the mast and the forestay. What this means is that if you just pull the forestay on to increase rig tension you will be adjusting the rake more than the rig tension!

Getting it Bent

With the mast straight from side to side the fore and aft bend needs to be sorted to match the luff curve of your sail read on.

The Rig Design

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

The Rig Design

Rig Tension

Most modern Cherubs use loads of rig tension - enough for many SMOD boats to just fold up! 200Kg plus on the shrouds is not unusual and often a lot more. The primary reason for using lots of rig tension is because the crew is on the trapeze. If you have 45Kg of rig tension on the windward shroud, the leeward shroud just slack, and the spreader holding the mast straight - as might be the case on a sit out boat. Then when your 70Kg crew gets out on the trapeze the windward shroud will go slack and there will be 30kg tension on the leeward shroud, with its spreader pushing the mast mid section up to windward, de-powering the whole rig. This is slow! Consequently, most boats start with 130kg plus of rig tension. On the other hand you have to be sensible with older boats. If I put the 180kg odd tension I use on the foam sandwich and carbon reinforced modern boat on a 3mm plywood topsides 1972 Farr then the poor old lady would just bend up and probably break. A good clue is to watch the foredeck as you put the rig tension on. If the boat is distorting the gunwales will spread between the mast and the forestay, and the foredeck will distort and go into humps and hollows. You have no foredeck? Another reason why its a bad idea to lose it! Obviously extra rig tension also tightens the jib luff etc, but I suspect that by the time you've got enough tension to make the spreaders work right with the crew bouncing on the wire the behaviour of the jib luff has ceased to be an issue. Its good to have the shroud anchorage’s as far outboard and aft as possible to reduce the peak loads when nose-diving etc, although obviously you also have to be able to let the boom out.

Standing Rigging.

Most boats have all the standing rigging made from stainless steel wire suggested sizes are

3mm dyform for main shrouds
2.5mm 1×19 for uppers
3mm 1 x 19 for lowers
2.5mm dyform for intermediates ( D2 to lower spreader root )

The advantage of dyform over 1×19 is that because it is made up from a smaller number of strands that are carefully shaped to fit to each other it will stretch less under tension leading to a stiffer rig unfortunately it is more expensive.

Exotics

There has been some experimentation with exotics such as “Vectran” and PBO which have the potential to give significant weight reduction over stainless steel and there will probably be more in the future. However the cost and difficulty in attaching them to the rig in a way that avoids any sharp corners has put many people off. One other disadvantage of composite standing rigging is creep. This is a property of the material and means that it will slowly elongate when left under load. This means that it will be difficult to keep the rig tension constant over the course of a day and repeat rig settings over the course of a year. Time will tell and as the cost of the material comes down and the terminating methods mature they will probably start to work their way into the boats.

Gooseneck Level Control.

Cherub rigs need to be strongly supported at gooseneck height. The short boom and big roach means there will be a lot of kicking strap load which will try very hard to bend the lower mast sideways and forwards dumping all the power. All fittings must be stronger than you think. Everything should be bolted on, and attached to something secure. If you have the slightest nagging doubt about something, it will break. Cherubs seem to put phenomenal loads on fittings, and most especially anything to do with lower shrouds. T terminals are the only choice in an alloy spar. Any kind of riveted fitting will either snap or pull through the mast. A plate round the mast front like an RS800 is one alternative. Another is to use wire loops around the mast threaded through the gooseneck. On a carbon mast T terminals are also OK. Another good alternative is stainless steel rings bonded on with a lot of Uni.-directional carbon wrapped around the mast. This has the advantage of not cutting any holes into one of the most highly stressed parts of the mast, however it must be done carefully to ensure that there is enough layers of carbon over the ring where the loads are highest. The other end should be absolutely rock solid, bolted, and ideally putting its anchorage in compression - e.g. running round the gunwale. A well-mounted plate loaded in shear will also be fine, but any trace of tension and it will just peel off. A stainless steel ring firmly located with a lot of unidirectional carbon is a good solution used on many foam sandwich boats.

One of the problems seen with older single spreader rigs especially when using a pole kite was that the mast would invert when going downwind. This inversion was caused by the tension from the kite halyard pulling forward well above the hounds To combat this many boats had what we in the UK call a prodder - a strut to gooseneck height from the foredeck. They do, of course, preclude self-tacking jibs. An alternative you will see is to have the mast supported by “rigid” lowers - struts to the gooseneck replacing lowers, which at the cost of a bit more windage lock the mast very rigidly. These rigid lowers can even be integrated into the boat by attaching them to gooseneck level stump that the mast sits on. The twelve-foot skiffs use a similar arrangement without the struts - just a post of truly massive construction integrated into the hull. This weight goes into the hull weight total and is towards the middle of the boat so its quite acceptable on a new boat. Unfortunately, the loads on the mast step at gooseneck level are magnified using this arrangement as all the kicker loads now go through the mast step without any help from the lower shrouds.

How Spreaders Work

Spreaders are used to support and control the bend in the mast they do this by deflecting the shroud away from the straight that it would like to take up. It is this shroud deflection that puts the force into the spreader that bends the mast. The greater the shroud deflection the greater the force that can be applied through the spreader to the mast. This means that the longer the spreader is the more effect it will have on the shroud and hence the mast.

If you look along the length of a shroud when it is under tension at where it passes through the spreader you can see what effect it is having on the shroud and so the mast. If it seems to be pushing the shroud forward then it is being used to help keep the mast straight and more rig tension will mean a straighter mast, if the spreaders are too far forward there is even the possibility of the mast inverting under excessive rig tension. If the spreaders are pushing the shroud back then they are trying to bend the mast and an increase in rig tension will only bend the mast further, which will work to de-power the rig

Single Spreader Rigs

This was the most common set-up prior to the extra sail area introduced in 1997 and will still be found on older boats. Two shrouds, one set of spreaders, lower shrouds to gooseneck height, and prodder - used as much to induce pre-bend as anything else, so needs to be strong in tension as well as compression. The lowers don't need to be adjustable on the water, but you need an easy way to tension them. A “Spectra” or other high tech rope lashing is as good as any, very cheap, and very effective, however they do make it difficult to repeat settings like you can when using standard chain plates. Although in theory raked back spreaders lead to better gust response. In practice on a older Cherub you are hunting for power much of the time, especially with a pre 94 rig, and so spreaders would be neutral or slightly angled forward against the neutral line of the shroud. This keeps the lower mast straight in conjunction with the prodder and lowers, leaving the top mast to flex and provide the gust response. This is probably still the best solution for a boat with an alloy mast. Tall alloy masts with twin spreader rigs seem generally to have too much weight aloft and performance suffers upwind. I think Andy Paterson was the only person to manage a competitive two spreader alloy rig. The spinnaker halyard can be appreciably above the hounds. You can probably go to about two feet or 60% safely, although this depends some on the mast section.

Twin Spreader Rigs

With the greater sail area since 1997 and the much lower weight of carbon spars these are pretty much universal since the sail area increase in 2005. The twin spreader rigs are required for the use of masthead spinnakers, without them you would need to use a tree trunk of a mast to keep it in one piece. A second advantage of the twin spreader rigs is that they support the mast sideways, helping to keep the power in the rig. When used with a lot of pre-bend the amount of sideways support given to the mast is adjusted using cap tension, and fine tuned using the Cunningham. As the Cunningham and kicker bend the mast the caps become looser, allowing the top to bend off sideways spilling the wind. There are a few different ways in which the mast and shrouds can be setup.

Diamonds

This rig configuration uses conventional spreaders to a conventional height. These lower spreaders are angled forward against the shrouds to lock the bottom of the mast fairly rigid. The masthead shrouds are actually diamond stays, normally running from the tip of the mast down through the top spreaders just above the hounds, through the main spreaders and then down to the base of the mast. There is a lot of variation in the staying arrangements. Many rigs use shorter upper spreaders, with the caps attached to the lower spreaders about halfway from the end to the root so that the main spreaders do not deflect the upper shrouds. The idea behind doing this is to isolate the control of the topmast bend from the control of the mid mast bend. The cap spreaders are generally heavily raked aft, introducing greater or lesser amounts of pre-bend, according to your sail cut. Some rigs have the caps pulling the mast forward at the lower spreaders and the shrouds pulling the mast aft and acting against the pull from the caps. This has the effect of locking the mast to a certain extent at spreader height and can mean that you can do without the D2’2 and all their extra windage.

C-Tech

By contrast the New Zealand designed C-tech rig has a lot of aft rake on both sets of spreaders and full length spreaders at the hounds. Typically, these are setup with the mast locked very straight up to the hounds with the D2’s trying to straighten the mast and the lower spreaders trying to bend it. Above the hounds they have a lot of prebend which is used to control the gust response of the mast.

49er style

With this setup the cap shrouds run from the tip of the mast through the upper spreaders, which tend to be quite long, and down to the shroud points. The main shrouds run through the main spreaders and down to the shroud points, and the lowers go from either the gooseneck or the top of the Gnav out to the shroud points. This setup allows for good sideways support for the top of the mast and it is also easy to adjust the tension in the caps when rigging. However as an increase in cap tension will decrease the main shroud tension, it can be difficult to control the middle of the mast and is likely to need quite long main spreaders set quite forward. This setup results in a high forestay tension and a large amount of the rig load passing through the boat, and would not be recommended for an older boat.

Attaching the trapeze wires

The trapeze wires should attach to the mast at about the hounds, and this gives a problem as you do not want to go drilling more holes in the mast than you absolutely need to. One option is to get stainless steel rings welded to the shroud T-terminals this is neat but getting someone who can do it without reducing the strength of the T-Terminal is more of a problem. Another solution is to drill a small hole through the upper spreaders and thread the trapeze wire through, chafing can be a problem with this method.

Gnav’s

A number of boats have recently started using strut kickers or Gnav’s ¹⁾. These add some extra windage and weight they also disrupt the shape of the mainsail on one tack. However they do open up a lot of extra space in the cockpit for the crew and in a 12 foot long boat that can make enough of a difference to be worth it. When using the Gnav the forward kicker loads act further up the mast and so the lower shrouds need to attach at the point where the Gnav fits the mast rather than at the gooseneck. As they constrain the bend of the mast about mid way between the

Over Rotating Masts - Wing Masts

It hasn't been done in this country for many a year, but in Australia a couple of boats have recently been seen with over-rotating semi wing masts, based on NS14 sections. This is a classic example of the wheel turning round, as such rigs were used in the early 70s, although the masts were spruce and balsa then. Such spars ought to be effective if you get them right. Supporting the bigger UK kites, especially masthead ones, could be a challenge, but it can be done - Alex Vallings of C-tech Spars in New Zealand has recently won an R Class Championship with a mast which has the tip supported by rotating spreaders. He tells a story of spending some time with a model made from broomstick and string working out how everything needed to be set up to avoid wires clashing as the mast rotates. In 2002 we permitted a mast with a greater chord than previously provided the area is measured in, and there is probably a performance benefit to be gained for a project with a considerable development curve. Bethwaite is good on the subject in “High Performance Sailing”.

¹⁾

‘Gnav’ is ‘Vang’ spelt backwards which is what the rest of the world call kicking straps

Building a Rudder Gantry

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Building a Rudder Gantry

These are by no means essential. They help keep the back of the boat clear and aid steering on a two sail reach. On the other hand the loads are tremendous and a failure is a guaranteed race loser. A rudder gantry isn’t that difficult an item to build, so here are a few pointers.

Materials

Successful gantries have been made out of:-

18mm diameter pultruded glass tube
Ordinary 1/2inch wood merchants dowel, reinforced with carbon or glass.
One inch balsa dowel core coated with carbon and glass
Aluminium tube
Titanium!
Foam Sandwich

The trouble is that unsuccessful gantries have been made out of just about all these materials too. The secret of a good gantry is the joining of all the components. The individual beams rarely fail, it’s usually a join or the attachment to the boat. If you stick some bits of wood dowel together and bodge it with a bit of epoxy filler it’s unlikely to stay together. Similarly if you attach a gantry - which creates considerable and variable tensile loads - straight to the outside skin of a foam sandwich transom the transom will delaminate and the outer skin will be pulled off. Aluminium - let alone Titanium - fabrication is a rather specialised area, and best left to those with appropriate experience. Aluminium gantries assembled from pieces bolted together tend to fail, and an all welded construction is recommended. Without specialist facilities and experience you will be better off using composite construction.

The Bars

A typical gantry looks something like this. It consists of two V shaped assemblies top and bottom to take the loads, plus a further tube running diagonally upwards from the centre of the lower assembly to the transom to brace the structure further. Depending on exactly how your boat is engineered it may make more sense to have this brace running from the top downwards. Ready made pultruded tube has got to be the easiest material for the bars. Glass seems quite strong enough, but you can use carbon if you want to. If you feel like it and can reliably make good solid tubes then you could make some and use those for the structure, but purchasing the ready made stuff is not too expensive.

Assembly

This is where the project will go right or wrong! I like to make up carbon brackets to join the components. I started by making up two V shaped assemblies for the top and bottom. The join was made by making two triangular carbon/glass plates, about 3mm thick, and gluing them each side of the horizontal tubes with plenty of strong (with microfibres) filler. When this was cured I drilled and cut it for the next join. The vertical piece (that the pin slides through) was glued into the holes drilled in each bracket, and then the diagonal brace in the slot cut in its bracket. At this stage the joins look something like this. Fill and smooth all the edges, fillet all the angles, and make all the corners nice and blunt. An angle grinder is quick and dangerous, a file slow and safe and essential in the trickier places. Now wrap every join with generous quantities of unidirectional carbon, and perhaps a layer of cloth over the top to keep all neat. Extend the carbon wrapping an appreciable way - maybe an inch - beyond the solid webs, and make sure that it tapers off neatly and smoothly to avoid “hard spots”. The webbing of the joints with the plates, plus the tapered carbon wrapping, is what gives the construction its strength, so fiddle though it is, don’t skimp this hassley job. The vertical tube can have nylon bushes top and bottom for the pin to save wear. If you have no other source buy RS400 ones!

Attaching to the boat.

Also vital. A solid stiff rudder and gantry assembly floating a few feet behind the boat has no effect on the steering! There is no substitute for having really stiff and solid mounting points built into the boat. Take the bars of the gantry right through the foam transom and glue them in with a nice strong filled mix. Cut them off flush with the inner edge, radiusing the corners. Cut some strips of unidirectional carbon about 4-6 inches long., “fray” one end, but leave the other end untouched. Wrap it into “sausages” and wet it out thoroughly with epoxy. You want to aim for enough strips that the sausages can only just be crammed into the end of the tube. Feed the good end into the bar for two or three inches, together with enough filler so that it is really thoroughly sticking to the inside of the tube. You’ll need to use a small stick or something, but really get it in there. Now spread the “frayed” end, about another 3 inches, all over the adjacent inner skin, so that it fans out in every direction. In this way the loads from the gantry come right through the transom and are well spread out over the skin, avoiding the risk of delamination of the transom. On wood boats the bars should come right through the transom beams and be well epoxied and filleted in.

Solid Gantrys

An alternitave to the tubular gantry is to build one out of sheets of foam sandwich, this has a number of advantages. At the end of a build you are likely to have enough off cuts of foam to be able to construct the gantry and the construction is no different from the rest of the boat. Another advantage is that it can be attached to the rest of the boat over a larger area reducing the point loading and the delamination problems that sometimes occur with tubular gantrys.

Fittings

A lot of problems with composite gantries and rudder stocks come when aluminium or stainless steel fittings are attached. It is virtually impossible to get a reliable bond between metal and composites. If you must use metal fittings then bolt them on solidly to ply pads - nothing else will do. Much better is to fabricate the fittings from epoxy/glass. A pintle will rotate just as happily in a glass tube as in a metal one, and you will find it a great deal easier to integrate the glass tube with the rest of the structure. No doubt it would be possible to create carbon pins for the male part of the fitting, but I prefer to have female fittings on both stock and gantry and run a single stainless steel pin right through the lot.

Building a Rudder Stock

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Building a Rudder Stock

Most Cherubs seem to get a number of rudder stocks over the course of their lives, as its one of the most popular breakages. It is also a good first project as provided you do it before your old one breaks you can still sail while you are building it.if it does not work you can always go back to the old rudder and stock.

Disclaimer This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. “Best practice” also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a composite structure without someone experienced in the materials to contact for advice.

Design

The “Dagger” or “Cassette” type of rudder/stock has a number of advantages over the fixed rudder or conventional lifting rudder. It is the construction of the dagger rudder that is described here. The Basic design has a sleave that closely fits the shape of the rudder blade that the rudder slides into. With a full length rudder pin that goes down through a hole in the tiller and another at the bottom of the stock.

The number one cause of trouble is an attempt to attach standard metal fittings the light weight glass or carbon structure of the boat or stock. It is supprizing how highly loaded the rudder blade is when the boat is going along and this puts huge loads through the stock and back to the boat all concentrated through the pintle and gudjion. Using the standard aluminium fittings gives problems with finding solid structure to bolt through and corrosion. The best method is to use a full length pin and construct the attachment bearing surfaces from carbon and glass.

The Sleeve

Start by moulding the sleeve around the rudder blade. Its difficult to take too many precautions against getting epoxy on the blade - lots of work to remove. Cover the top half of the blade with parcel tape, with it overlapping the trailing edge of the blade, and apply release agent or candle wax. Suspend the board with the leading edge horizontal and uppermost. Laminate the case using an appropriate layup (100 g/m² glass + 2 x 200 g/m² carbon or 4*200g/m2 glass would be fine, allowing the fibre to overlap past the trailing edge. When its cured, trim the case to about 2mm oversize. Split the case from the foil, and add several layers of 18mm masking tape plus parcel tape to the trailing edge of the foil to make a thick edge to the foil. Replace the blade in the case, fill the open joint at the trailing edge, and laminate strips of glass around 20mm wide over the joint, with kevlar at the bottom (all held in place with masking tape). Its probably also worth putting a few layers of glass extra at the leading edge, as it tends to get a lot of bashes as you pull the blade in and out. When cured remove the sleeve, remove all the packing from the blade and make sure it slides very easily through the sleeve. If you can't slide the sleeve off the blade at all, or if it seems stiff on the blade, then cut it neatly down the trailing edge and try again with more layers of masking tape! The sleeve will need to reach from the top surface of your stock to the lower edge of the bottom fitting. These means about 75mm greater than the distance between fittings, but make it bigger and trim later!

Lining the Sleave

Some people like to line the sleave with a soft slidey material to protect the blade from scratches and make it eiser to pull up and down. Materials that can work are

loops side of velcro
Felt or thin carpet
ProGrip (Padded but not slidy)
Jap Tape

These can help make the blade fit more snugly but if they start to come off inside the stock they are a pain to replace.

The Bottom Fitting.

This is a favourite breakage point, and needs to be stronger than you'd possibly believe! Dave Roe reckons that the peak sideways load on the rudder stock is in the close order of magnitude of 180Kg or 400lbs. If you want a mental picture of this imagine the boat sitting on its side with 80 (Eighty) bricks piled up on the top of the blade. Start by laminating up a solid carbon plate, about 4mm thick, about 75mm longer than the section length of the rudder blade, and 75mm wider than its thickness. This needs a great many layers of carbon cloth, and make sure that the fibres are aligned both 45/45 and 0/90 degrees to the blade. This is a great time to use up all those odd bits that have been accumulating in the plastic bag of offcuts in the garage. If you are worried about point loads from the plate acting on the foil or are planing to use a T-Foil rudder, then glue a piece of 8mm foam onto this, and then cover the other side of the foam in a couple more layers of carbon cloth the thickness will help the bottom plate resist the upward forces from a T-Foil. Andy Paterson finds this unnecessary for a standard rudder. Anyway, either way we now have a substantial black plate. Cut a hole in this so that it fits over the sleeve at 90 degrees to the foil with (of course) equal overlap. You may wish to have the plate angling up about 15 degrees fore and aft to clear the stern wave, but this depends a lot on your rudder gantry. Between the two you probably want the aft end of the plate about 100mm above static waterline. Make sure that the sleeve fits freely - its very easy to squash it so that the blade won't go through. When you are really happy with the fit (check three times!) then glue the bracket onto the sleeve. Use a nice strong filler mix - there will be load on this so use some microfibres and silica along with the light stuff. I suggest you wrap the foil in plastic again and put it through the sleeve to make sure it still slides freely while the glue is setting. Give a nice generous fillet with your favourite light filler between sleeve and plate, and put a layer of glass over the fillet - it all helps distribute the load evenly onto the blade.

The Tiller

There are a lot of ways of doing this. I suppose the best, especially if you happen to have a handy bit of carbon tube lying around, is to make the tiller from a piece of tapered carbon tube, cut a slot for the sleeve, and glue it in a similar way to the plate. You need to be quite careful about the tube you pick, especially about the resulting thickness at the leading edge of the blade where a lot of tube is cut away. I guess a lot depends on how much extra carbon you put on. My normal method is to make a rectangular section core - on the last one I laminated up several layers of foam, ending up with a core about 50mm deep and 75mm wide at the pin, tapering to about 20mm by 75mm at the trailing edge, and 50mm by 25mm at the extension. This gives a shape something like this. Don't forget to put some high density foam or a wooden pad in the tip where you will be bolting on the tiller extension. Andy does it slightly differently. He uses exclusively HD foam and makes it 20mm thick tapering to 10mm and 60mm wide, tapering to 10mm, with an oval section rather than rectangular. Opinion varies greatly how long the tiller should be. Basically the shorter it is the more room you (or your helmsman) will have round the knees when hanging desperately off the back corner on a nasty pitchpoling 2 sail reach, but the greater the loads will be. I think my stock on Halo Jones is about the shortest, 540mm from pivot to tiller extension, and most are probably nearer 700mm than 600.

Now its time to get the fibres on. My memory is very vague about what I used. I *Think* I used a layer of 200 g carbon cloth, aligned 45/45 on all four faces, plus two layers of unidirectional carbon on the sides, plus another couple of layers of carbon cloth top and bottom around the pin/leading edge area where the big loads are. Finally I gave the whole thing a couple of layers of 200g glass top and bottom, and overlapping the sides to keep all the carbon in place. As ever compress the layup - for this a Workmate and parcel tape is helpful. Andy's recommended method is to laminate 1 layer + 1/2 layer uni-directional carbon (300g/m²) tape x 100mm , plus 210g/m² glass (spiral wrap of 50mm wide strip). This spiral wrap seems to work well and squeezes the excess resin out and holds the carbon down). Anyway, once you have done that you can glue the tiller onto the sleeve. Basically the same technique, but this is your last chance to check that you have the distance between the two pieces correct, so measure lots of times. I tend to have a small fillet at the top, so the sleeve extends slightly above the tiller, the idea being to distribute the load from the top skin.

Pivot

Finally its time to put the pivot in. Ideally you will have some pultruded glass tube exactly the right size for the pin. Believe it or not this is available! If not then make your own by wrapping cloth round a very well waxed pin, but you'll probably need to ream it out after the layup has shrunk on curing. Either way drill through your tiller and bottom late with a drill big enough for the glass tube. If the bottom plate is solid, not partially cored, then you don't need the bottom tube, just make the hole big enough for the pin. There are spectacular loads coming through the pin, and it needs to be very strong. I dig out the foam core next to the skin top and bottom of the hole and create a void that can be filled with filler. If the core is high density foam then this is unnecessary. Glue in the tube., again with a very strong fibre and silica rich filler. It is essential to have the pin in while its setting to keep the top and bottom lined up, and equally essential to be very careful to make sure the pin is exactly in the middle and exactly parallel to the rudder blade. When the pivot tube has set put some more carbon round it to make sure that the loads are thoroughly transmitted to the skin, not the core. Get a good bit of reinforcement just at this point, because its a real trouble area. The bottom plate can be trimmed to a more streamlined shape if you like, and certainly round off the corners. You will probably need to shape it rather more round the pin to make sure it doesn't hit anything. Have a good look at the “stop points” on maximum steering. You don't want the sleeve to get bashed if you jam the tiller hard over. Make sure that something substantial takes the thumps when you jerk the tiller hard towards you in a desperate attempt to bear away. If necessary build a couple of carbon stops. Finally fill, fair and paint as you deem necessary, then bolt or screw on the tiller extension. Now you can go sailing again!

Based on original by Jim Champ July 1999 (with considerable input from Andy Paterson).

Running Rigging

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Running Rigging

Main Sail

Mainsheet.

There are two popular mainsheet systems, the fully centre mainsheet like a 420 and the aft led forward like the 29er .

Fully Centre

With this method the mainsheet is kept in the middle of the boat often using a bridal or a post to help to centralise the boom. The advantage is that it is easy to swing a single tiller extension around the back you do not need to go for twins. The disadvantage is that it takes up a lot of space in the middle of the boat and it is hard for the crew to take the mainsheet as they have to hand it back for each tack or end up in quite a tangle.

Aft Led Forward

With this system you have a block on a bridal at the back of the boat, the bridal is set up so that the block sits just below the boom when the main is sheeted in as hard as it can be. The mainsheet is tied to the boom, goes down through the block then back up through a block on the end of the boom and forward to a block in the middle of the boom. A lot of people will have a ratchet block there and hand the mainsheet to the crew. If you are doing this with a self-tacking jib it is a good idea to tie the mainsheet to the jib sheet so that they are both accessible from the wire. If your helm insists on taking the main sheet then they can still do that with this system either by taking it directly from the boom or down and through a block on the deck and a jammer,. If using this system it is worth putting a loop of cloth or webbing to run the sheet through to stop it from falling down and lasooing the helm during tacks and gybes. The main disadvantage of this system is that it is not possible to swing the tiller extension around the back during manoeuvres, it either needs to be short enough to go around the front, impractical if the helm is wiring or twin extensions are necessary one each side.

Kicking Strap

The kicking strap, or Vang as the rest of the world calls them, purchase should probably be 16/1 or 24/1. It all depends on where the take-off on the boom is, and how low the other anchorage is all parts of the kicker system need to be very strong. If you are using a carbon boom then to spread the load a webbing strap should be used. Proctor make very good and extremely expensive ones for the 14s, but any sail maker will be able to oblige. A cascade type purchase is most common, but care needs to be taken to ensure that you have enough range to cope with the full range of conditions. Dave Roe uses an old fashioned differential winch, but with rope rather than wire, and this certainly makes for a much cleaner boat, although no-one else does this.

Gnav

An alternative to the conventional kicker is to use a Gnav, ⁵⁾ this uses a strut to push down on the boom to have the same effect as the kicker. A verity of methods have been used in other classes to do this, the 29er and 49er use a leaver arrangement where pulling on the leaver effectively makes the strut longer pushing the boom down. However this needs careful set up of the size and shape of the leavers plus the complexity adds weight. The system most commonly used on the Cherub to date is to have a strut with a fixed point on the mast and a slider on the boom. As you pull the slider along the boom towards the gooseneck it pushes the boom down. With the Gnav set up you need to attach the boom solidly to the gooseneck as there is a force pulling the boom away from the mast. The lower shrouds also need to go to the point where the Gnav attaches to the mast and not the gooseneck as with the standard Kicker arrangement.

Cunningham

You will need at least 6/1 Cunningham with a Mylar mainsail, and probably more. You can use any method you like for this but cascades are quite common. One important tip with the cunningham - attach it to the boom. What I mean is that the fixed end of the purchase needs to be pulling up on the boom. This means that the ciunningham load offsets the kicker load and thus reduces the strain on the gooseneck fitting. Don’t laugh - they break!

Outhaul

The outhaul does not need a large amount of adjustment when you are sailing and a lot of people just use a piece of string lead through the clew and back to a slot in the end of the boom. A series of knots in the string provide all the adjustment that is needed. If you have an adjustable outhaul then it is best kept internal to the boom with a cleat on the underside at the forward end. A block positioned just in front of the cleat will let you get a good pull a 6/1 purchase will be enough to make life easy.

Control Line leads

The Kicker and both need to be adjusted as conditions change on the race course and as you round marks so they should be easy to reach. Where the lines are lead is a matter for personal preference. If you are twin wiring with a regular crew then it is probably easier for them to make the adjustments, however if you are single wiring and swapping crews each time you sail then it is best set up so the helm can reach them. A good compromise is to have the control lines lead out to the gunwales on each side near the middle of the boat this allows either the helm or the crew to adjust depending on who has a free hand at the time. When deciding where to position the control lines it is worth thinking about elastic takeups. There is nothing worse than a tangle of string floating around the bottom of the boat and elastic is often the only way to keep it under control. If the control lines are lead to each side then sewing the ends together to make them continuous is a good idea as you do not want to run out of kicker when trying to bear away in heavy weather. An alternative to using controls lead to each side is to have a single control line on a swivel cleat in the centre of the boat, however the tail of this needs to be tied to something so it is accessible from the trapeze. The tail of the mainsheet is a good option for this.

Main Halyard

If you sail somewhere with restricted rigging space you may feel that you want a main halyard although most boats just use a loop of string to tie the sail to the top of the mast. If you are going to go for a halyard remember that a 8:1 Cunningham will put quite a load on to it so it will need to be strong. The best bet is to go for a 2:1 on the halyard this reduces the compression in the mast and makes it eisier to pull the sail up. Because spectra is slippy you may have problems keeping it in the cleat in this case you could splice a loop in your spectra halyard and use a hooked rack to hold it in position.

Jib

There are two main set-ups for the Jib, dual with the one sheet for each side of the boat, and self tacking where you have a single sheet to hold and the jib swaps from side to side by sliding along a car.

Self Tacking Jibs

The sailing techniques are different, especially upwind, where you don’t just leave it and forget it - see the heavy weather sailing article. They’re best done with a track and roller bearing car - the smallest available say Frederiksen 020. The track is bent to slightly less than the radius from the tack of the sail to clew. The track is bent in one plane (forward but fitted angled up slightly , i.e. the ends are slightly higher than the middle). The ends are fixed in foam/carbon supports, and one screw in the middle into the mast step structure. It’s a very good idea to have two bolts in the track at the ends, because if the track comes undone you will not only break the track, but also lose all the bearings out of the car. You also tend to hold on to the track launching, so it needs to be pretty substantial. The track is angled/bent/fitted so that heavy sheet tension will pull the car to the centre of the track in no wind. The wind pressure in light winds and low sheet tension is enough to move the car to the ends of the track. In stronger winds it also works fine, but needs rubber stops at the end of the track.. In general people don’t seem to have stops for sheeting angle, so it would be wise to have numbers or marks on the track. Sheet tension varies the leech tension as required. The pulley on the track is surpassingly tricky. It wants to be as light as possible for light airs, but it takes a lot of abuse when the jib flogs. A block with plastic cheeks will wear though quickly, and it takes quite a bashing so should be strong. From the car the sheet is lead to a block as far forward as possible then back under the foredeck, it is a good idea to have a 2;1 purchase here so to reduce the loads on the crew and let them make finer adjustments to sheeting position. Most people have a swivel jammer not unlike a mainsheet jammer for the jib, and a single sheet. This is probably neatest. And if the crew is doing the mainsheet the two can be tied together ensuring that both are available from the wire. An alternative would be to split the sheet to each side and run them to a conventional sort of location. In any case remember the crew or helm will still need to play the jib sheet on two sail reaches and while tacking. And just because there’s a two to one purchase don’t use a thin rope. The crew needs to be able to use the jib sheet to pull themselves back to the boat if you teabag. Given a 4mm line and a cold day this just doesn’t happen. Trust me in this! The clew position on the sail is crucial. You’ll probably end up getting the sailmaker to change this once the set-up is all sorted out. Mutiple holes on the jib clew give you a choice of slot angle/twist in the jib against the sheeting angle. It can be a good idea to add backing lines. These are a couple of light lines running from the car to the shrouds on each side, long enough not to restrict the normal movement of the jib. If you need to back the jib for some reason then pull on the line. To heave to between races hook it over something handy! But if you find they get snagged take them off, they’re not that vital!

Dual Jib sheets.

They can be led to anywhere convenient, with a jammer that can be freed and jammed from just about anywhere in the boat, since the crew will be trapezing right at the back of the boat on windy two-sail reaches. Inboard from the shrouds is a good place, out of the way but accessible. Continuous jib sheets are popular. Sheets should be long enough for the crew to be able to fully free the sail from on the trapeze at the back of the boat. If they are too short you will regret it! The jib slot normally has a lateral control on a short length of track. About 3” of movement is all you will ever need, but if you don’t know where that 3” is going to come you will want it longer. A lot of people have a height control, but it can be as simple as a cleat on the track, because you usually adjust it on the opposite tack. Don’t clutter up the crew’s area with a lot of string designed to let you adjust the slot in any direction at any time. He’ll only trip over it and fall out on the last tack when you were about to win your first Cherub race.

Jib Cunignham

The jib Cunningham is used to adjust the tension in the luff of the jib this has an important effect on the shape of the sail but you are unlikely to need to adjust it too many times on the water. A four to one lead aft to a cleat hidden under the foredeck is all that is needed for this if you really want one.

The Spinnaker

The adoption of asymmetries has simplified spinnaker handling a lot. There is no spinnaker guy or pole height adjustment , and the sheet is really easy to handle and rarely cleated

Launch and Recovery

A continuous halyard with chute system is normal, with the chute or hatch about a foot behind the stem to reduce tangles with the jib foot. The halyard and the retrieve should be arranged so that helm or crew can handle it. The halyard exits the bottom of the mast is optionally used to pull the pole out, it then should come back into the cockpit to a cleat. A block should be positioned about a foot aft of the cleat so that the line cleats when you pull through the block. From here the halyard should go back to another block near the back of the cockpit and then forward through the spinnaker sock and up to the retrieval patches on the spinnaker. There are normally two or three patches on the spinnaker so that it will fit into a shorter sock. A book could be written on systems that will automatically uncleat the halyard on the drop, however a simple method is just to grab the halyard between the cleat and the first block and just pull on the retrieval side, by the time you have got it tight the chances are that you will have uncleted it.

Pole

Two String Launch

The following is probably the simplest system to rig and set-up and is best used if your pole is untapered or has a lot of friction. The Tack of the kite is attached to a “guy” coming through the pole and to an anchor point in the boat. Its set up so that the line is taut and the spinnaker tack pulled right down to the pole end when the pole is pulled right out. A second line runs up to the bow and back to the end of the pole to pull the pole out. Depending on the friction in the system and the strength of the crew you might wish to have a 2/1 purchase on this. There’s no retrieve for the spinnaker pole as such, the act of pulling the spinnaker back into the chute is enough to bring it back in.

Single String Launch

This is a system where the halyard is used to pull the pole out, this means that there is only one string to pull on the hoist but you do have to pull that string harder and for longer. If there is a lot of friction in the pole launch system then it will not work. When the spinnaker halyard exits the bottom of the mast it needs to go through a block and forward to a floating double block and back to the cleat and the rest of the system as normal. The pole is launched by the floating block being pulled backwards pulling the pole launch line one end of which is tied to the forward bulkhead the other end is goes through a block and back to the inboard end of the pole.

Bob Stay

If at all possible have a spinnaker pole strong enough to be unstayed. But if your spinnaker pole isn’t strong enough to operate without a bob-stay then the best way of arranging one is to have the “guy” running through the end of the spinnaker pole and out again and then down to the bow. In this case the line is tidied up by having it pass through a ring or pulley inside the pole, which in turn is pulled back with shock cord. This works well enough, but you’ll probably need a little more purchase on the outhaul to make sure the bobstay is tight enough. You might get the occasional snaggle inside the pole too. The anchorage at the bottom of the bow is also a problem. Apart from the water resistance if its not made strong enough you can pull the bottom of the stem off.

Spinnaker sheets

These are invariably continuous. Ratchet blocks are essential, The size and shape of the spinnaker will govern the position that the turning block will end up if that is too far aft you may need to lead them forward to another block to keep them out of the way of the mainsheet. Most boats with snouts have a hollow in the gunwale line between the snout and the shroud. This makes spinnaker sheets especially prone to be washed into the water on the beats. Andy Paterson has small “hooks” made from very flexible polyethylene on his gunwale. Flick the sheet onto this and it stays on board, but they’re too soft and flexible to snag anything or damage the spinnaker. Again sheets should be long enough for the crew to be able to fully free the sail from on the trapeze at the back of the boat.

Other Spinnaker Gear.

When the spinnaker is in the bag an elastic take-up system can be useful for the loose part of the halyard, one way of doing this is to have the elastic set up so that it goes through a block on the forward bulkhead then back to the end of the pole. This system means that the elastic tightens when the pole is retracted sucking up the exess halyard and tidying up the boat.

Rig Tension

A jib halyard is basically a device to put a 2/1 compression load down the mast. As no one uses a forestay you can’t take the jib down while sailing, and rigging a boat on its side is so much more civilised. Have a wire strop and a T terminal, and use a short lashing to get the tension. The problem with this method is it can be prone to some stretch while sailing loosing you your rig tension it is also difficult to repeat your settings. If you want a more positive system you can use a jib luff wire that hooks into the mast with a T-Terminal and has a chain plate at the bottom. You need a boat breaker to pull the tension on but when it is on it is going to stay there and you can be sure that you are using the same rake as the day before.

Unnecessary Gear.

Adjustable standing rigging has never been used in Cherubs. Its heavy, expensive, and complicated. Just getting the simple sutff to work right is enough of a bother. Kevlar ropes are best avoided they have a tendency to break with little or no warning just throw it out it is not worth the bother. Most of all, remember that the boat is weighed dry. Take all those ropes, weigh them, soak them in water and weigh them again. The difference will amaze you!

Don’t spend too much time worrying about gear. Instead go sailing! Provided all the gear works and is reliable then it is probably good enough. Being able to change the sail shape in the middle of the race is unlikely to make much difference to your final position, but capsizing at every gybe mark certainly will. There is absolutely nothing that improves boat speed as much as crew speed! Finally

Keep It Simple Stupid

⁵⁾

Vang spelt backwards

Sail Numbers

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Sail Numbers

The sail numbers are internationally allocated in blocks:

1451-1550 UK
1551-1650 ?
1651-1750 UK
1751-1800 ?
1801-1850 Aus
1851-1900 Aus
1900-1950 ?
1951-2000 NZ
2001-2100 ?
2101-2150 UK
2151-2200 Aus
2200-2250 NZ
2251-2300 ?
2301-2350 UK
2351-2400 Aus
2401-2450 UK
2451-2500 Aus
2501-2550 UK
2551-2600 NZ
2601-2700 UK
2701-2750 NZ
2801-3000 Aus
3001-3050 Italy
3051-3200 Aus
3201-3300 UK

Navigation

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

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Making a Spinnaker Pole

anonymous@undisclosed.example.com (Anonymous) — Wed, 01 Mar 2023 18:04:09 +0000

Making a Spinnaker Pole

At some point in your Cherub sailing life you will probably need a new spinnaker pole either because you break one or you just need a new one to support your upgrade plans. Obviously this will have to fit inside the support tube in the bow or snout of your boat and yet retract into the boat possibly past the mast to meet the class rules. If you are replacing a broken pole you only have to copy the existing dimensions. If you are building a new boat or modifying an older one you will have to spend a bit of time working out how long and how tapered it needs to be. This article is based on advice in an email from Gavin Simms who has made 4 poles in recent years, some modifications have later been added by Roland Trim.

Starting from Scratch

If you are building a new boat or modifying an existing one you have a bit of measuring and design work to do. It is no point making a shiny new pole and finding it won’t fit your boat or jams during every drop. The variables you have to play with will depend on how early you are in your design/build or how much modification you intend to do.

Firstly the pole has to retract into the boat and satisfy the following rules.

4.2.3 Bowsprit - The bowsprit, if fitted, shall be retractable to within 4.3m of the transom.

The outer end of the bowsprit shall be solid or capped. No sail other than a spinnaker may be

set from the bowsprit.

The first thing to look at is how far back in the boat the pole needs to retract this will determine your problems.

If when retracted the inboard end of the pole is still in front of the mast then no problems, if it is between the mast and the centreboard you could either bring the pole to one side of the mast or stump or under a mast bridge. If it comes back behind the centreboard a mast bridge has to be quite large. If the pole needs to retract to one side of the mast the pole will need to be tapered to give slack in the snout when retracted.

Critical Dimensions

As mentioned above there are some basic measurements which will affect how your pole retracts into the boat not to mention how strong it will be.

Distance from mast to outboard end of pole. (This is determined by your spinnaker luff length, the boat’s mast position and mast rake.)

Length of pole outside the boat.

Length of support tube.

Inside diameter of support tube.

Distance between inboard end of support tube and mast.

Wall thickness of pole

Diameter of inboard end of pole

Diameter of outboard end of pole

Decisions on Dimensions

If we take a hypothetical boat with some simple numbers we can assume that the boat has a bow at 3.7m from the transom and the end of the snout is 4m from the transom. The mast is 2m from the transom and leading edge of the centreboard in 1.7m from the transom. The pole while extended must reach 6m from the transom. (Note these numbers are simplified to make the maths easier a boat may or may not work with the bits in these positions.)

With these basic numbers in place I can work out the required length of the pole. This is governed by the position of the aft end of the bow tube. I am going to put this at 3.6m from the transom. The pole length is therefore 2.4m. Meaning that when fully retracted the aft end of the pole is 1.9m from the transom. In this case we can either go for a bridge or bring the pole to one side of the mast.

To bring the pole to one side we need to check the taper is adequate. The greater the taper of the pole the more slop there will be when the pole is retracted, however an overly small tip will be hard to build and thread with the string, correspondingly a large aft end will take up a lot of space in the boat.

Things that affect deflection of the retracted pole are.

Length of Bow tube; longer tube, the smaller the possible deflection.

Taper of the pole; the larger the taper the larger the possible deflection

Position of Mast; mast set further back require poles with less taper to achieve the same deflection.

Spreadsheet

A spreadsheet was developed to work out the required dimensions for the pole and snout for one boat assuming a non tapered bow tube. This should be treated with care as the assumptions made about the geometry may not be the same as for this boat, however the pole made using this fits the boat with a few mm to spare.

Cherub Spinnaker Pole.xls

Loads

Steady loads

The pole is under a bending load from the luff of the kite. This is difficult to determine but very roughly should not exceed the weight of the boat. (Note that helm and crew will be hanging off the back end) in strong winds. Add a factor of safety of 4 to account for most shock loads and capsizes.

Shock loads

Most poles appear to break when the boat is pitch-poled. Gav recalls most of his poles breaking in a big pitch-pole. This appears to be irrespective of how strong the pole has been made. Consider the force of the boat and crew (230kg) slowing from 20 knots to zero knots in a couple of seconds and the forces involved. It is worth noting that making a very strong and stiff pole will transfer the loads of the pitch pole on to the support tube and hull possibly breaking the next weakest area. It is therefore much better to have a pole with some flexibility that can absorb some of the impact so the inboard end of the pole doesn’t see such a sudden high instantaneous load.

In all circumstances the highest load will be at the inboard and outboard end of the support tube. The pole will have to be thicker at these points to maintain the shape and hence avoid buckling.

How the laminate works

When bent, the material under the highest stress is on the outer surface of the pole. One side of the pole is under tension and the other is under compression. Therefore the outer layers of the lay up must be able to take these stresses or transfer them to the layers beneath. The bonds between each layer must be good and the pole should ideally be made in one session. Biaxial cloths have been suggested to be good at transferring stresses to the layers beneath and many yacht spars are made incorporating several biaxial cloths within the mainly unidirectional laminate. Cherubists commonly use plain weave cloths as the first and last layers with uni layers in between. Plain weave is used in other parts of a cherub so the choice is often made for cost and availability of materials. recent thinking suggests a second biaxial or plain weave layer on the inside of the pole at the point it exits the snout. This should help to stop the pole buckling at the point of the maximum bending load.

Once you have designed your pole to fit your boat, things get more interesting.

Preparation

All successful laminating jobs depend on good preparation. Once you have started you have to keep going to avoid the first layer curing before you have finished laminating. Make sure that all materials are available, cut to the right size and that tools are to hand. It doesn’t hurt to have spare mixing pots, sticks and brushes, gloves, in fact anything that might be needed. I would even turn off my phone to avoid any disruptive calls.

The Mandrel

If your pole has to be a certain diameter and taper you may need to make or purchase a bespoke mandrel. If you can find a suitable mandrel you may decide to design your pole around this.

In the past tapered windsurfer masts have been used as mandrels. Gavin Sims has a tapered aluminium mandrel that is 2“ wide at the base and a bit less than an inch at the top. His poles have been 2.1m long so the mandrel will be a bit longer. If you need a longer pole (Some are nearer 2.8m long you will need to find another mandrel or some how extend the tapered one at the outboard end.

Paul Croote found himself in this situation and made the mandrel for ‘Cheese Before Bedtime’ by laminating timber around a steel tube. He then turned the timber down on a lathe to produce the taper. The inboard end was about 80mm in diameter so quite different from Gav’s, however Paul did have a full workshop at his disposal. More info about this process can be found on Cheese Before Bedtime own page.

The outside diameter of the pole is critical. Too big and it won’t fit in the boat. When choosing your mandrel ensure that you have accounted for the thickness of the laminate and any protective layers between the mandrel and the pole. (ie. if using the candle wax release method).

A tapered pole should be made over length and trimmed once fitted to the boat as the exact position where you get a tight fit with the boat will depend on the thickness of the laminate and any protective layers.

Preparing the Mandrel

Once you have found or made a mandrel for your pole you have several options to make it slippery enough to stop the pole from sticking to it and to get the finished article off.

If the mandrel is smooth and non porous and you want to reuse it, coat it with several coats of mould release wax.
Alternatively and more low risk is to coat metal mandrels with a thick layer of candle wax. This is melted out once the pole has cured allowing the mandrel to fall out. There is more on this on the Building Carbon Masts page
If you are less confident with the surface finish of your mandrel or it is made from a more porous material, I would recommend an alternative. Cover the mandrel neatly with parcel tape and wax with mould release wax. Then wrap the mandrel with a layer of Mylar film (drafting film) and cover with more parcel tape. Avoid sticking the parcel tape to the mandrel itself. Don’t substitute the Mylar for cling film because true to its name it will cling to the mandrel.

The Lay-up

Starting from inside going out

1 x 200g plain (or biaxial) carbon
4 x 300g unidirectional
1 x 200g plain (or biaxial) carbon

With a tapered pole you need to taper the width of each section of cloth to maintain an even laminate thickness along the length. Twisting the unidirectional cloths slightly along the length of the pole in opposite directions for each layer will also help increase the strength in torsion.

Of course you may not want an even laminate if what you want is the lightest possible pole. As the loads on the pole are higher at the inboard end particularly where the pole enters the boat it may be worth tapering the laminate even more to get a decrease in laminate thickness along the length of the pole. If this is done then the outer extremity of the pole should be strengthened to give it enough strength to cope with the point loads from the tack line.

As soon as possible after laminating the laminate should be wrapped in heat shrink tape being careful to keep the side with release agent against the laminate the heat shrink tape should overlap by at least half the width of the tape, the more the better. Once fully wrapped and with the ends secured the shrink tape should be gently heated with a paint stripping heat gun. This will consolidate the laminate and squeeze any excess resin out, sometimes at high pressure so safety glasses are a must, an eyeful of hot epoxy is not fun.

Alternatives to heat shrink are wrapping the laminate in strips of peel ply or glass tape.

Vacuum bagging has also been used in recent poles, but is considered by some to be difficult to avoid creases. For this instead of heat shrink, a tight overlapping helical layer of peel ply is added, then appropriate breather and it is all placed in a plastic bag and the air sucked out of it. The vaccum consolidates the layup. If using this method the home build advice is to leave any hoop fibres in the layup for a second hit (i.e. inner hoops and uni first, layer of weave over the top added as a separate hit). Thick vac bags appear to also result in creases, use of very thin plastic (decorators dust sheet) is reccomended by some for spars. The mast and pole on several of the recent boats (all spars on EJ) were made using this method.

Getting it off the Mandrel

Be prepared - it is hihgly unlikely that the pole will simply slide off the mandrel. You generate alot of friction just consolidating the layup and the laminate shrinks slightly on curing. There are may diffferent methods but the following may help you think of some more:
1) Rotating the pole against the mandrel often means you are only stressing a small area of bond. So twisting can help.
2) When pulling off a mandrel you are likely to release all of the bond at the same time, bits can go flying at this point as the energy in the ropes is released accelerating freed objects.
3) If pulling be careful of damaging things. Tow bars can bend and you will want that to tow the boat with. A non vehicle technique using two trees and a “spanish windlass” may be less fun, but can generate higher loading with no risk to your chassis or your clutch.

On the other hand, for some using a truck is part of the fun:
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Finishing

Using the above techniques and spec you can create a stiff and tough pole. But if you are after a better finish you should leave off the final weave in your laminate. Once the laminate has cured you can fair out any bumps or hollows to get a smooth base for the final layer of weave. This should either be done with a UV resistant epoxy or top coated with a UV resistant lacquer.

What Happens when you put the Kite up?

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

What Happens when you put the Kite up?

Towards the end of 1996 there was a long thread in the rec.boats.racing newsgroup about the effects of asymmetric spinnakers on the trim of a boat. Basically the discussion was between those who sail such boats, and those of a more mathematical disposition. The former reckoned that the moment you put the kite up the bow lifts, the whole boat steadies and pitchpoling becomes less of a problem. Therefore the kite must be lifting the bows of the boat. The second group worked from the logical viewpoint that the result of a large sail pushing the boat along from a centre of effort well above the water can only be to press the bows down. The strong views expressed inspired Mikko Brummer, of WB-Sails, Finland, to model an asymmetric rig (actually based on the pictures of my Cherub from this site) into his company's sophisticated mathematical model of a sailboat rig. This article is prepared from his original paper, published on his site, and the copyright for the data is retained by WB-Sails. The conclusions however are my own, and Mikko is not be held responsible for inaccuracies or errors in them. To summarise Mikko's findings, the rig creates a great deal of upwards force which must have a big effect on the performance of the boat - and certainly explains the ever increasing tendency of Cherubs to “get some air” from wave tops in extreme conditions. In spite of this there is no doubt at all that the drive from the spinnaker presses down the bows.

This table summarises some of the main figures.

Sail	Drive Force		Lifting Force		Heeling Force		Heeling Moment		Pitching Moment
	kg	lbs.	kg	lbs.	kg	lbs.	kg/m	lb./ft	kg/m	lb./ft
Spinnaker	68	150	60	132	52	114	129	87	172	115
Main	36	79	7	15	28	62	80	54	117	78

Thus in this model the rig is producing an upward force of 67kg - around a quarter of the total weight of boat and crew. If you add to that the considerable upward force created by the shape of the hull. The dramatic effect the spinnaker has on the performance of the boat in this situation is also well illustrated. Even the mainsail is displaying a small amount of lift due to the rake of the mast and bow-up trim. I must apologise to the purists for displaying the forces in kilograms and pounds, but I felt this would be more understandable than the technically more appropriate Newton.

Graphic - Computer wire frame image of Cherub Rig.

This side elevation from the computer model demonstrates the way the combination of bow up trim and mast rake enables both mainsail and spinnaker to create an upwards force. In my opinion, bearing in mind this data, the reason why the 3 sail reach feels so much steadier and seems to require less hanging off the back of the transom must be to do with secondary effects, and not directly caused by the lift from the sail, which is most definitely pitching the bow down. One can then speculate on what these effects might be.

The first must surely be the “ reduction” in displacement caused by the lift from the sail. Its well established within the Cherub fleet that heavy crews have much more trouble with nose-diving and pitchpoling than light weight ones. Whatever causes this effect, which one presumes must be partly to do with the shortness of the boat, a reduction of effective displacement of the order demonstrated above must bring it into play.

Other forces that seem likely to have an effect on this phenomenon are to do with the differences between the mainsail and the spinnaker. In his (highly recommended) book, High Performance Sailing, Frank Bethwaite notes that a sail that has a long leading edge angled to the apparent wind (like a delta wing of an aircraft) can develop “roll-over” vortexes which scrub stagnant air off their suction (lee side) surfaces. This mechanism can maintain attached flow up to abnormally high angles and create a great deal of lift (and drag). Thus the low aspect ratio spinnaker should be much less sensitive to changes in its angle of attack caused by gusts, the boat rocking, accelerating or decelerating in waves etc., so the power produced by the rig should, I think, be much more even. In addition on a two sail reach the main - which produces its energy further above the water than the more triangular spinnaker - is the main source of power, whereas on the 3 sail reach it tends to be used more as a “trim tab” to control the pointing angle and is less often fully powered up. Therefore on the two sail reach the ratio between drive force and pitching moment is less, and the delivery of power from the rig is much less even. My memory is that the two-sail reach unsteadiness was much less of an issue a few years ago before we all adopted the very rigid stable and low twist mylar sails of today.

I'm not sure how reliable these figures are as an emulation of actual sailing performance. Any kind of mathematical model is only as good as the data you can put into it, and ideally one would like to feed in some real data from measured performance on the water. Mikko has assumed an “across the deck” wind speed of around 20kts, apparent wind at 70 degrees to the centreline, and a forward velocity of around 15 knots. My guess - and it is a guess - is that in the real world this would be a slightly atypical situation, and that with 20 kts across the deck one might be sailing to best advantage with the apparent wind a little further forward of the beam. However short of putting a full set of instrumentation on a boat the only thing you can do is to put together some best guesses.

The following tables are extracted from Mikko's paper. Elsewhere on the WB-Sails site are more details on the mathematical modelling techniques he uses, as well as some information on their practical application.

Asymmetrical - section forces [N] & moments [Nm]

Section	DriveF	SinkF	HeelF	HeelMom	Yaw Mom	PitchMom
1	24	-13	12	3	1743	-19
2	143	-97	141	151	5116	77
3	182	-122	153	143	2646	332
4	171	-140	124	408	-1247	533
5	123	-161	73	311	-3031	585
6	26	-53	10	48	-558	174
Total	669	-586	513	1265	76	1682

F stands for force (in [Newtons]. 1 N = 0,1 kg = 0,2 lbs.) Mom stands for moment Section 1 is at the foot of the sail, 6 at the top (every section between the red lines). The third column, SinkF, is the sail force component perpendicular to the sea surface. Negative sink is LIFT, so the kite is lifting the boat at a force of 586 N, or about 59 kilos.

MainSail - section forces [N] & moments [Nm], including mast

Section	DriveF	SinkF	HeelF	HeelMom	YawMom	PitchMom
1	46	-5	38	31	-2691	42
2	78	-9	61	102	-5615	142
3	73	-11	56	145	-6003	207
4	65	-12	49	174	-5760	250
5	60	-15	46	205	-5461	293
6	35	-12	23	125	-2052	211
Total	356	-65	273	781	-450	1146

WB-News articles index

WB-Sails Ltd Oy Tiistinniityntie 4, FIN-02230 Espoo, FINLAND tel. +358-0-803 6833, fax +358-0-803 6830

Spreaders

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Spreaders

Design

Classically spreaders served to push the shrouds away from the mast, thereby improving the sideways force on the hounds. This means they were in compression, and some even had a hinge at the mast end!

Now they are used to push/pull the middle of the mast, which mean very great bending loads are put on spreader. This means they need to be strong, and attached across the whole diameter of the mast.

Spreaders also take a beating when rigging or when carelessly stood upon in the boat park.

All of the above means you need to put quite a few fibres running in all directions when making spreaders. We did this with guidance from Dave Roe.

The length of the spreader and the angle of the spreader are not covered in this article, but I will say that if you have shrouds which go to the mast by the spreader roots (called D2's or D1's), then you need the spreaders to be angled back such that they are pushing the middle of the mast forwards against the D2's holding them back. If you don't have D2's then you want them neutral or forward so they keep the middle of the mast back.

Build

Foam

Decide on the length (you can always trim / extend them later), and draw out an isoceles triangle which is the length of the spreader long, and the base is the diameter of the mast. Make the pointy end not a point, but cut it off to make an edge about 15mm long.

Cut this shape out with four thicknesses of 8mm 80kg foam. Glue them together in pairs using some epoxy and some filler (doesn't matter which) to make two 16mm thick rather boxy foam spreaders.

Go to the movies while it is all going off in the oven on a low heat (55 degs C is about right)

Shape the foam with 80 grade sandpaper. Keep the bottom flat and just sand the top until you have something that looks like a spreader. Try to make a smooth taper to about 6mm thick at the pointy end.

Gouge out the flat side at the thim end so a part of a stainless chainplate can fit in flush and bog it in there, and smear the entire surface with a trace of the epoxy filler mix.

Carbon

Put the spreader down on a bit of newspaper and draw round it. Roll it over like a rolling pin and draw round that, and do it again until you have gone round 3-4 complete revolutions. You'll end up with a shape on the newspaper like half a flower, as the spreader will turn as you roll it. Do it again with the other spreader.

That is the shape of the carbon cloth you will need. Any kind of 200g weave will do. We used plain weave, but 2:2 twill would be fine.

Cut out enough peel ply to completely cover each spreader once, plus a bit of overlap.

Cut out two bits of carbon to match the shapes marksed on the newspaper.

Wet out the cloth on a big sheet of plastic.

Apply the spreaders and gently roll them up in the carbon. The conic shape of the spreader ensures that the fibres will run in every direction, giving the properties you want.

Add the peelply and use the convex shape of the spreaders to really yank on it hard to help consolidate the layup.

Stick it back in the oven and go away.

Finishing

When it has gone off, pull the peelply off and enjoy your handiwork.

Make the spreader a good fit to the mast by using a holesaw with the same diameter as the mast at the thick end of the spreader. Don't forget the spreaders will want to be angled up to bisect the angle through which the shroud is turned. The easy way to work this out is that the upward gradient of the spreader = 0.5 * the distance from the spreader to the hounds along the mast / the length of the spreader. “A bit” is usually the answer to that equation.

Bog the spreaders on. We used a hot glue gun to attach them instantly before a big fillet and 2-3 layers of carbon went on.

Tidy up. Go sailing.

Building a T- Foil Rudder for a cherub.

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Building a T- Foil Rudder for a cherub.

Most of the Ideas for this came from looking at the back of several International 14s and reading all the chat that has gone on about T foils since I first saw them in Beer on the back of Paul Bieker's 14. I have never studied hydrodynamics or any kind of boat building so all my sizes and construction methods are more “best guess” than calculated.
The basic idea of the T-Foil in the boats like the i14 and the Cherub is to lift the transom of the boat while going upwind allowing the crew to sit further back. So that their weight is taken on the more hydrodynamically efficient foil rather than just through displacing water. Or, while planing, from the flow over the lower surface of an incredibly low aspect ratio foil (The hull).

The problem is that when you are going down wind the last thing that you want to do is to lift the transom thereby pushing the nose down. To get around this the angle of attack of the foil must be adjustable so that you can neutralize the lift and even go negative for the bearaway and the downwind leg. Over the years the two main designs that have evolved are the Bieker system, where the horizontal foils are supported on a central axle and are made to move up and down using a rod down the center of the rudder, and the Fixed Foil system where, the whole rudder, stock and pintle is moved in order to change the angle of attack. I decided that the Fixed Foil system having less moving parts was going to be easier to construct in my garden shed so this is what I will describe. For a bit of comparison have a look at a Video showing the transom wake two Patterson 7's “AquaMarina” and “Little Red Number” sailing in light winds Aqua with a T-foil and LRN with a standard one.

There are three main parts to the T-Foil system as used on AquaMarina:

The Rudder with horizontal Foil
The stock
The control system

The Rudder

I decided to build a separate rudder for the T-Foil rather than modifying my current rudder so that if the system did not work or broke I could still go back to the original and should not lose too much sailing. This also meant that the control system on the back of the boat had to be backwardly compatible with the old rudder and stock.Rudder Before Assembly I started off by building a foam carbon rudder with a bit more carbon uni’s towards the trailing edge of the blade than normal to take the loads transferred up from the horizontal foil. See technical article on building a rudder blade for the general idea on how to build the blade. The basic T part of the foil was planned to be a symmetric NACA four digit section but ended up being a bit thicker and out of shape due to some build errors and not taking into account the thickness of the laminate properly. The first forizontal foil that I made was 1,000mm long with a max thickness of 10mm and a chord length of 100mm. Unfortunately it broke due to just being carbon and a foam core with no real crush resistance. Due to the loads the central foam crushed reducing the thickness and therefore the strength with the inevitable result. The second Horizontal foil is 900mm long (being the length of wood that I had.) with a chord length of 100mm and a max thickness of 13mm. It was built on a cedar core with a layer of 200g woven carbon followed by three layers of 200g uni’s tapered in from the center. The center layer was approx. 100mm next 300mm and last 700mm long it was finished off with a second layer of 200g carbon cloth and a 150g glass cloth all hand consolidated with a layer of peel ply.Rudder Assembled

I then cut a hole in my newly constructed rudder around two thirds of the way down slotted in the horizontal blade made sure it was all square added a bit of filler and carbon to hold the two bits together. Then it was just a matter of fairing the whole thing smooth.

The Stock

The stock is constructed in the same way as a normal dagger rudder stock the only differences being that you must be able to insert the rudder from the bottom as the T will stop you from inserting the rudder from the top. It will also need to be a bit stronger than normal as it is not only taking the normal rudder loads (bigger than you might think) but also the lifting loads from the T-Foil, which could be somewhere in the region of 60 to 80kg. Attachment for the pintle rod also needs to be further away from the rudder blade especially at the top to give room for the adjustment mechanism. You are looking to get a total of 9 Degrees of movement, from Plus 7 to Minus 2. So the actual range of movement at the top needed depends on the distance between the top and the bottom gugion but with a distance of 20cm a bit of trig gives the answer as just over 3cm. There also needs to be a way of locking the blade down so that it does not lift up with the lift from the foil I used a hole saw the same diameter as a piece of aluminum tubing to cut through both the rudder and the stock. With the tube tied to the rudder with a piece of elastic it is simple then to stick the tube through the hole when the rudder is down to lock it in place.

The control Mechanism

The basic idea behind the control system is to give you the scope to easily change the angle of attack of the horizontal foil without upsetting the feel of the helm too much. This is done by moving the axis of rotation of the rudder blade, the pintle rod, in relation to the boat, while keeping it parallel to the rudder. Effectively this is done by rotating the 8mm stainless steel rod which acts as the pintle about the bottom of the gantry and allowing the top of the pintle to slide backwards and forwards in a slot at the top of the gantry.The control of the system is done using a pusher rod which forces the top of the pintle rod back in the slot thus increasing the angle of attack of the T foil. The drag from the water and some elastic is used to pull the rudder forward again. The push rod is moved using a six to one purchase lead to a cleat on the front of the gantry. The bottom gudgeon was made by adding an extension to my existing gantry out of a bit of foam with a thick layer of carbon plate on the bottom this was then covered in carbon top and bottom to make a nice solid base. A hole was then drilled on the centerline for the rudder pin to pass through. This hole had to be filed to an oval shape to allow the pin to rock back and forward as the angle of attack is altered. In practice I found that after a few days sailing the carbon had warn away and the pin was now sloppy. Bolting a stainless steel plate to the bottom so the plate takes the sideways loads and the up loads are still taken by the carbon cured this.

The pusher rod is made from a stainless steel block welded to a bit of 8mm stainless rod. It fits into a short section of glass tube, which was made by wrapping the glass around the well waxed piece of 8mm rod. This tube is then mounted on the top of the gantry on the centerline in such a way that it will bear on the pintle rod. To make the top gudgeon I made up two carbon plates and placed two 8mm rods between them to hold them parallel then a bit of carbon over the end to hold the whole lot together. This was then offered up to the boat and with the pintle rod and the pusher rod in position holding the whole lot square and parallel the whole lot was wrapped in plenty of carbon. With the addition of a 6:1 purchase to pull the pusher rod back and a cleat fitted to a bracket that I made for the front of the gantry the control system was complete.

Using the T-Foil

Launching

Thanks to the wings the rudder had to be slotted in from the bottom of the stock. Take the boat out to thigh depth water then tip it over about 30 to 40 degrees. The rudder then slots in to the bottom and the boat can be brought upright with the tip of the rudder sticking about 10cm below the bottom of the boat. Once in deep enough water push the rudder down and put in the locking tube and the system is ready to go.

On the Water

Upwind the foil is used to stop the transom dragging and take some of the weight of the boat. In practice you set the foil to the angle of attack that you want and then use your weight to trim the boat to the same sort of attitude as it would have been if the foil was not there. The lift generated by the foil depends on both the angle of attack of the foil and the speed of the boat through the water. To keep the boat trimmed correctly it takes a bit more body movement than normal, as when the speed of the boat changes the lift generated by the foil changes and so you need to move your weight to counteract. In lighter winds I used less foil as I did not want the drag penalty, moving up to maximum as my crew moved on to the wire. In stronger winds when you are overpowered as the speed of the boat increases you need to reduce the angle of attack as the foil will now be generating more lift than is needed. In general the foil needs to be adjusted less than the kicker

Bearing away and downwind

It is vital to let off the foil before bearing away or a capsize is inevitable. Downwind the boat feels a bit smoother slightly less bouncy but there is not much difference from a standard foil. A few times we tried pulling the foil on a bit in light I am not sure whether it helped or not. In theory if it gets really mental it would be possible to set the foil slightly negative but I have not had the chance to test that yet.

Returning to shore.

With the locking tube removed it is straight forward to get the foil up till the blades touch the bottom of the stock this still leaves enough to steer by. Once out of the boat just tip it over a bit and the foil can be removed from the bottom of the stock.

But is it quicker?

I think that there will be a bit of a speed penalty down wind but hopefully the improved upwind speed will more than pay for it considering how much more time I think that with practice it will be quicker especially in the marginal tricky zone for cherubs. In ghosting conditions one would expect it to be very slightly slower. In mental conditions one might expect it to be v marginally slower, but more controllable so it's probably worth it.

Setup a T-foil Rudder

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Setup a T-foil Rudder

In the past few years the T-foil rudder has enjoyed increasing popularity in the UK-Cherub class. This page aims to look at the different systems that have been used on various boats and the advantages/disadvantages of each.

Basic Principles

The basic principle of the T-foil as used on the Cherub and other classes such as the International 14 is to use the lift from the foil to reduce the displacement of the boat, this helps to promote planing. As the lift is produced by the rudder at the stern this will tend to lift the stern and push down on the bow. Moving the crew weight back in the boat will counteract this returning the hull to the correct trim. The movement of crew weight is effective when going upwind, however down wind it is not possible to get far enough back to keep the transom on the water and the bow up. To prevent undesirable bow-down trim (and possibly an unstoppable pitch pole) when going around the windward mark you need to reduce the lift from the foil. The easiest way to do this is to reduce the angle of attack of the foil. Typically the range of angles required are from plus 7 to minus 2 degrees. The boats t-foil system will need to be able to cope with adjustment across this range without any adverse effects on the boat.

The system should be easy to adjust while sailing as having the t-foil in the wrong configuration will slow you down upwind and could lead to a pitchpole downwind. Many systems use a control line lead to the sidedecks for adjustment and are used in a slightly binary fashion: On upwind and Off downwind. Having the adjustment setup so that twisting the tiller extension controls the angle of attack has the advantage immediate adjustment. The ability to do this is of particular importance when using the foil down wind as with a bit of foil on the acceleration from a gust can lead to a serious nosedive. However if the loads on the system are high then to get a low torque on the tiller extension a powerful gearbox is required meaning that many turns of the tiller are required for the full range of adjustment, making the adjustment at windward mark rather slow.

System Requirements

Strong enough to take the loads from the rudder and T-foil.

Adjustable to give a range of angle attack from approx +7 to -2 degrees.

Allow full range of motion with limted play or distortion of the system.

The feel of the helm should not change too much over the range of motion.

Easy to make both small and large adjustments in angle of attack.

Light.

Low Drag.

Names of Things

Stock Typically of the dagger type where because of the blades of the T-foil you have to insert the rudder in from the bottom

Pintle The Vertical pin that the rudder rotates around as you steer.

Gudgeon The holes both on the rudder and boat that the pintle fits through

T-Foil The horizontal lifting foil parts of the rudder.

Systems in use

Rotating Pintle

The basic idea of the rotating pintle is that the entire stock including pintle rotates to change the angle of attack. The pintle stays at the same angle to the rudder throughout the range of motion so that the feel of the helm does not change very much. All the adjustment is done on the boat so any weight is measured with the boat giving a slight decrease in overall sailing weight. One disadvantage is that as the adjustment system is on the boat it works best using a control line lead out to the sides, it is tricky to set the system up with a tiller twist grip.

The push rod system on AquaMarina and Primal Scream allows the pintle to rock back and forward around a fixed point at the bottom, but with the top able to slide forward and backward giving the motion. A rod with a block on it pushes against the pintle to increase the angle of attack. In light winds some elastic can be used to pull the pintle forward again.

While the system is simple it has limited range of movement limited by the gap between the pintle and the leading edge of the rudder. Also the bottom gudgeon for both the rudder and boat needs careful design to avoid wear as it is highly loaded yet needs to cope with movement of the rudder in two planes. While it would be possible to route the control system up to the tiller twist grip with this system there are problems with the large loads involved and steering affecting the adjustment.

Rotating Gantry

With the Rotating gantry system as used on Atum Bom the entire gantry rotates. It is held on two bearings on the back beam of the boat and is controlled using a purchase from the deck to the gantry that prevents the gantry from rotating to decrease the angle of attack, it is held up using some strong elastic. This system has the advantage that there is no real restriction on the range of possible movement, all the adjustment system is part of the boat so is included in the measured weight It may be difficult to eliminate slop in the system and if you get wear in the bearings they would require a major rebuild to repair. Contrary to what may be thought, there are no serious consequences of a failure in the control string: The unrestricted t foil adopts an angle of about -3 degrees and flies along like an upside-down kite, only floating up when the boat stops. Although the main control is through a string system to a cleat in the boat, this system has also been setup with a twist grip tiller, because of the positioning of the block there is a slight change in angle of attack when steering. In addition because of the high load in the control line a large purchase is required to make the twist grip work this means that it takes many turns of the tiller extension to get a significant change in angle of attack.

Rocking Plate

An alternative approach to the rotating Gantry is the rocking plate system as used on Ronin. This uses a plate with gudgions on that rotates around a bolt in a carefully profiled gap in the gantry. This system can have a larger range of motion than the push rod system and because the pintle is fixed with respect to both the rudder and the rocking plate it is easier to make the gudgions tight and wear resistant. To keep slop to a minimum the gap that the plate sits in must be a close fit and needs careful design to ensure that grit or sand does not cause jamming.

Rotating Stock

With the rotating stock as used on amongst others Subtle Knife, Cherub Dæmon the pintle is fixed with respect to the boat and all adjustment is kept within the stock, this has the advantage that no modifications need to be made to the boat when retrofitting. In addition it works well with the twist grip tiller extension. To provide the angle of attack adjustment the pintle is allowed to slide back and forward in a slot in the top of the stock extending into the tiller. The movement is controlled by twisting the tiller with the direction changed through a gearbox and the mechanical advantage gained through a worm drive. Care needs to be taken to ensure that through the range of motion the interface between the bottom gudjions remain wear free at all angles of attack. One disadvantage of this system is that as the angle between the pintle and the rudder changes so does the balancing or feel of the helm. This will typically lead to a light helm upwind and heavy downwind. The range of this motion needs to be carefully setup so that the feel of the helm does not become either too heavy or overbalanced and too light.

Rotating Foil

With the Rotating Foil system as used on the majority of Beiker Int 14's and }} the blades of the T-foil itself rotate with respect to the rudder this allows the t-foil to work without changing the positioning or feel of the rudder. There is not much force required to move the blades and all the adjustment is contained within the rudder so this system is ideal for using with a twist grip and no modifications need to be made to the boat to fit. The disadvantage of this system is that to give enough strength in the axle the blades often need to be slightly thicker than those directly attached to the rudder. In addition to keep slop to a minimum the tolerance between the axle and bearing in the rudder need to be tight with many “International 14's using titanium axles.

Flexible Flap

The Flexible flap is the system favoured by the International Moths and was used by Shiny Beast at the Nationals in 2005. The Flexible Flap system has a fixed T-Foil with the back third able to rotate. The flap can either be attached using a piano type hinge or a section of silicone rubber or rubbery epoxy impregnated Kevlar. As the Flap moves this changes the profile of the t-foil changing the amount of lift generated. This is effective for small angles of flap but at large angles the sharp change in shape at the hinge point becomes quite high drag. Again because the system is entirely held within the rudder it is easy to setup with a twist grip tiller.

Building Foils

Building a T- Foil Rudder for a cherub.

Building a Rudder Gantry

Kevin Ellway T-foil article (Members Only)

Technical Support Contacts

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Technical Support Contacts

To support Cherub owners the Class Association has a network of people around the country who are experienced in the construction and maintenance of the boats. If you have any questions or problems please contact them. The chances are that they will be able to point you in the right direction straight away, and if not they will know someone who can.

Scotland

Phil Alderson
phil_alderson

Northern England

Neil Cardno
neil_cardno

Midlands

Simon Roberts
simon_roberts

East Anglia

Ben Brown
ben_brown

Wales and the South West

Gav Sims
gav_sims

South East England

Will Lee
will_lee

Wooden Boat Expert

Tom Kiddle
tom_kiddle

Technical Information

anonymous@undisclosed.example.com (Anonymous) — Thu, 09 Mar 2023 08:24:52 +0000

Technical Information

Dinghy sailing in the UK experienced massive growth in the 1970's through the introduction of strong glues and ply construction. This allowed the construction of strong light boats by the average person in their garage. With the development of fibreglass and foam sandwich construction many other classes have lost their home build roots The Cherub class has always encouraged development and home building and has proved that it is quite possible for the amateur to design and build their own boat using advanced materials and techniques.

As such the UK-cherub is one of the few classes in the UK where the majority of boats have been launched and raced by their builder. This passion for boat building is not just restricted to new boats, many older boats have been rebuilt and upgraded through their lifetime and this has lead the impressive lifespan of modern Cherubs.

We try to provide instruction and guidance to newcomers to the class to help them repair their boats and get them up to speed quickly this includes regular class run “sticky weekends” where any member can bring parts and get help with fixing them.

Thinking of building a Cherub?

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Thinking of building a Cherub?

If you are thinking of building a Cherub it can be confusing getting to grips with all the different parts and stages of the build. This website contains a wealth of information on most of the techniques required; however it can be difficult navigating around the index and finding what you need. This page is intended as an overview of the build process together with links to more in-depth articles. This article will mostly look at building a modern Cherub using foam sandwich construction, other methods are possible and articles covering different techniques have been linked. Some of the articles are linked to more than once as they often cover several sections.

Note: This page is being used as a handy reference to the articles that we have and to work out subjects that need expanding, links to articles that exist are in green and those that have yet to be created are red. It is in a very early stage at the moment, all members please help to fill it out.

Building a Cherub can be broadly divided into several stages:

Designing
Mould
Hull
- Under Deck Structure
- False Floor and foredeck
- Various Semi Structural Items and hard points
- Fairing and Painting
Fitting Out
The Rig and Spars
Foils

Designing

The Cherub is a development class with quite open rules so there is the oppertunity to build your boat to your own design, it is not the only way as there are a number of proven designs out there and a small fee to the designer will let you build the design and probably get advice for the build along with the design.

To get some idea about the principles involved in the design it is worth reading the Designing Cherubs as well as some of the other pages we have covering the subject.

Mould

In order to build a hull you need a design and then a jig or mould built to that design. There are two main types of moulds the male mould and the female mould. With the female mould the boat is built inside the mould and with the inside skin of the mould conforming exactly to the outside skin of the boat. This is the method normally used with production boats and can produce good results with very little fairing needed on the outside prior to painting, however this type of mould takes much longer to build and needs careful preparation before use. The most commonly used type of mould used in the Cherub fleet is the male mould. Here the hull is built on the outside of the mould with the outside skin of the mould being the same size as the inside skin of the hull. This means that the size of the mould needs to be adjusted to the thickness of the foam used. Also the outside skin will need more fairing to finish the hull off, however many people consider that it is possible to build a lighter hull this way.

If you are going to vacuum consolidate your hull as you lay up then the mould must be built in such a way that it is airtight and you have a platform around the edge of the mould that you can stick the vacuum bag to. The mould is normally built by placing thin strips of wood over a series of frames, the wood strips are cut to be as close to each other as possible with filler in any gaps that are left. It is quite common to cover the mould in a layer of glass cloth for extra strength. This is then faired and covered in a release wax so that it is possible to get the hull off! There are a number of moulds floating around in the class at the moment and a simple option is to borrow one of those and build a boat on it. This saves the time and cost of building a mould yourself although you do have to arrange to pick up and return or store the mould when you have finished with it. If you do not feel that you have the expertise for building the mould and hull shell then there is always the option of getting this part of the hull built by a professional and then completing the bare shell yourself. This can be quite a good option as you know that the hull a major part of the boat has been properly built and is light weight this may enable you to complete the rest of the hull without having to invest in a vacuum pump.

A Jig which the foam is attached to and then the outside skin is laminated. Once set the shell is removed from the jig and the inside skin laminated.

A Male mould, the inside skin is laminated, then the foam then the outside skin.

A Plug and Female mould, the plug is created in the shape of the boat, a female mould is then made on the plug, which is removed. The hull can then be built in the female mould, with the outside skin laminated first, followed by the foam and inside skin.

Hull

The Hull is built using a jig or mould to give it the designed shape and to support it during the build process. The Hull is either build on the outside of a jig or male mould or the inside of a female mould. When building over a male mould you will laminate the inner skin, possibly using a vacuum bag to help consolidate, then the foam is cut and shaped, this is probably the most time consuming stage as this will dictate the fairness and precise shape of the finished hull. Once the foam is in place the outer skin can be put on. At this point it is ready to come off the mould. Building in a female mould can be slightly quicker as the outside of your hull will already be fair when it is removed from the mould, however the mould takes much longer to build and prepare.

This can be quite a good stage to get a professional to build to, it saves you the problems of building or transporting a mould and you know that a major part of your boat has been properly done.

Tips

Put peel ply onto the mould in the positions where you are planning to attach bulkheads, fittings or intend painting this can be peeled off after the hull is taken from the mould leaving a clean area with no release wax for further building.
Some types of foam can be softened using a heat gun allowing them to be bent into shape more easily.
To shape some foam around a particularly tight corner, it can be scored with a knife in a series of lines along the direction of the bend.

Under Deck Structure

This primarily consists of the bulkheads and spine together with the centreboard case. The layout of the bulkheads is partially governed by the requirement in the rules to have 3 separate buoyancy tanks.

The two main layouts are

One tank forward of the shroud bulkheads and one each side of a solid spine aft of the shrouds
Three tanks across the boat with one forward of the shroud bulkhead, one between the shroud bulkhead and one in the middle of the cockpit and a tank between the mid bulkhead and the transom.

Bulkheads that are not used to seal buoyancy tanks can have large parts cut away to leave a lattice work to provide the support where needed. As the bulkheads are just flat panels they are quite easy to build but if you are building without a vacuum pump it may be a good idea to buy these pre laminated by a boat builder. All that is required is to cut them to shape and fit them. The closer the fit of the bulkhead to the hull the less filler that is required for a strong joint, helping to reduce weight. A good fit can be made using plywood off cuts as templates, these are cut and sanded to shape, this shape is transferred to the bulkhead panel which is cut out and sanded to a tight fit.

The bulkheads are typically just filleted to the hull, again using a small fillet is good for weight. It is often worthwhile reinforcing the joints of shroud bulkhead and around the mast step with some cloth to spread the load. The Centreboard case also needs to go in below the floor, it is obviously important to get this aligned along the length of the boat on the centreline, it also needs to be perpendicular to the bottom of the boat. This is definitely a case of measure twice and cut once. The centreboard case needs to be securely fastened to the bottom of the boat and be thick at the back as repairing a damaged case after the boat is built can be a nightmare.

Tips

Make a pattern for the bulkheads out of scrap ply, then draw around where the bulkhead is to be cut and sand to an exact fit.
When placing the bulkheads ensure that the positions line up with the position of various structural components of the boat.
When gluing the centreboard case into the boat put the board in the case (covered in tape) this ensures that the case is not distorted and that the board will go in and out.

Crew Deck and Foredeck

The Crew Deck or False floor goes on top of the Bulkheads and provides a lot of the strength in the boat and also somewhere to stand while sailing the shape and height can make a difference in how the boat is to sail, how quickly the water drains and where the various parts fit. The false floor could be made from flat sheet , however it is probably best to build it with some curve in it. This can be done using a mould to support the deck while it is build but also using the bulkheads to support it and give shape. To build a mould-less deck, cut the foam for the deck to size so that when weighted down it will fit neatly to the top of the bulkheads. With the deck flat on the ground laminate what will become the underside, leave for long enough for the resin to green but not go hard and lift the deck onto the boat, weighing it down with as many weights as you need to get it flat. The boat should be protected with polythene or parcel tape so that you can remove the deck after it has cured, it may also be worth fitting temporary battens to the sides of the boat between the bulkheads to help with the support. Once cured the deck will hold its shape so can be removed, trimmed and fitted properly, then the top surface can be laminated.

A foredeck is optional, some boats have them and some do not, it is largely personal preference whether a foredeck is fitted, however if one is not used then some other way must be found replace the stiffness that the foredeck provides. There are a number of boats that use a mini foredeck to support some of the shroud loads and locate the jib track.

Major Structural Items

Consisting of the larger more heavily loaded parts of the boat, these include;

Snout and Bowsprit support
Shroud and Forestay Supports
Wing Bars
Gantry

These parts of the boat are all quite highly loaded yet still need to be built light and integrated carefully into the hull. The integration is where the biggest gains in structural weight and overall stiffness can be made. You need to think of the loads these items are likely to see not just in normal usage but also in unusual situations such as grounding, collision and rigging failure. You need to visualise what these loads are doing and how they are passed into the hull, how they are trying to fold the hull and what structure you have to prevent this. In many cases you can move some structure about a bit so that structural items can serve more than one purpose. With the advent of the t-foil the gantry needs to be much stronger than before and it was already a heavily loaded part of the boat the attachment of the gantry into the hull structure is more important than before. The Shroud and forestay points are obviously important to get right, many boats have used shackles or D rings effectively tied into place using unidirectional Carbon. This is a good technique but sufficient layers, particularly over the metal of the D-ring, must be used to ensure the point load is spread out into the structure.

Minor Structural Items

Consisting of smaller lighter components in the boat consisting of but not limited to;

Spinnaker Chute
Centre Console
Kick Bars
Hard points for fittings

The design of all these is incredibly variable and the best way to work out what you want is to have a good look at peoples boats and ideally sail in as many different designs and styles as possible. In general when attaching these items you need to try and ensure that the fibres run in the best direction to take the load and that there is enough material around the attachment points to effectively spread the loads away from the point of attachment. There are as many ways of attaching fittings as there are fittings, with foam sandwich construction it is not a good idea to screw fittings in place as they will quickly pull free. Simply bolting fittings is also problematic as the bolts can easily crush the foam and pull through the thin laminate.

Fairing and Painting

Can make or break you boat, It is important to fair the hull skin so that it provides a nice smooth bump free surface for the water to flow across, however using too much filler will result in a heavy boat and sanding all your laminate off will result in a weak boat. Fairing the inside of the boat is even more difficult, the corners and edges are particularly tricky to sand and there is a penalty in leaving too much filler on the boat, but no speed advantage once you have the main rough bits smoothed out. The lightest filler possible should be used and it can be tinted with different colours to help you see where you are in the sanding. Cherubs are typically built without gel coat as it is heavy and can only be used when building in a female mould, this means that they need to be painted. There is quite a tradition of wild paint jobs in the Cherub class so there need not be any restriction on your imagination when deciding the colour scheme. Cherubs have been successfully painted with everything from standard exterior gloss to metallic car paint to two pack polyurethane. They have also been badly painted in most of those things as well. The key to getting good results is ensuring that the substrate is sound and clean, each layer is compatible with the one below and that it is applied in clean dust free conditions in accordance with the manufacturer’s instructions.

Fitting Out

The fitting out stage is great fun as you can see your boat getting closer and closer to the water, it also takes more time than you expect as the list of different jobs to be done is surprisingly long. Typically cherubs are fitted out as simply as possible, however the systems you need still add up and fitting them into a small boat it is easy to make it look crowded. Controls that are needed are;

Mainsail
- Kicking strap, gnav or temple vang
- Cunningham
- Outhaul
Jib
- Self Tacker Track
- Jib Sheets
Spinnaker
Sheets
Halyard and retrieval line
Pole outhaul
Tack line
Trapeze lines with elastic takeup
T-Foil control

To get all those to work you need quite a lot of fittings and string, you also need to attach them to your boat, this can be tricky with a foam sandwich construction as it is poor at dealing with point loads. Screws will not last and even bolts will pull through unless large washers are used. Some methods used for attaching fittings are outlined below;

Plywood core – During construction the core is locally replaced with plywood. This gives a strong area to bolt or even screw fittings to, however overtime the plywood will absorb water and rot.
Core Replacement – The holes for the fitting are drilled through the top skin of the sandwich only, then using an allen key in a drill the foam is crushed around the holes, the voids are filled with filler and the fitting can be bolted in place.
Carbon/glass Backing plates – In areas where access to both sides of the structure is possible you can cut out a section of 3-4 mm thick carbon or glass plate slightly larger than the fitting to be attached, this spreads the load over a larger area.
Fronting Plates – A backing plate is made up and the fitting bolted to it, the bolts are then cut to length and the nuts bonded to the backing plate. This plate with nuts on is then bonded to the deck of the boat and glassed over the top. As the nuts are now captive the fitting can be removed and replaced as necessary. This is particularly on the false floor of a boat where you cannot get to the inside.
Tying – Self explanatory but with the number of blocks that are designed specifically for tying in place it might be worth designing in some points that they can be tied to rather than adding weight by bolting a fitting in place and tying to that.

The Rig and Spars

For the rig and sails you can do as much or as little as possible, many people build their own booms and spinnaker poles and a few people even build their own masts and sails. Home built masts used to be extremely common in the Cherub class, however the production masts have come down in price and improved in quality to a point where buying one in is a good option. For those on a budget repairing a broken mast from another class can be a good option but will not be as good as a custom built one. For the rig to work well together it is important that the sails match the weight of the crew, the boat, the bend of the mast and the way the mast is rigged so it is worthwhile talking to a sail maker early in the project to work out the optimal layout for you.

Foils

There are a good many people who will build excellent foils for you and a few who are closely connected to the class, however building something like a rudder or centreboard is an excellent introduction to high tech composites and often a good starting place to see how you enjoy the epoxy fumes and dust involved in a boat build. As said before the centreboard needs to be done before the false floor goes in so that you can build the centreboard case around it. The rudder can wait till the end of the build but having a completed boat just waiting for something to steer it with is not much fun.

And Finally

Other bits you may need at some point include a road trailer with launching trolley, a cover to protect your boat from the elements and some foil bags to keep them from damage. There are quite a few different articles on the website describing most of the build techniques many of them are linked to from this article but the rest can be found in the Index of Technical articles Cherub sailors are always keen to help with advice for building projects and the class runs regular sticky weekends where there is informal instruction and parts are built for newcomers to the class there is also a technical help network.

Good Value Tiller Extensions

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Good Value Tiller Extensions

When you start helming from the wire you need a longer tiller extension and because they tend to break when you fall on them this can get quite pricey as they need to be about 2m long. With a bit of ingenuity you can make your own extension without spending too much

Version 1 The plumber

Difficulty - low

Get a length of 22mm or 30mm PVC drain pipe cut to required length. Fit the UJ in the bottom and attach with a screw or bolt. If you are using a 30mm tube you will need to pack the tube with tape or foam to get a tight fit for the universal joint.

Advantages

This type is dirt Cheap at approx £3.50 for the tubing which, is available from any good DIY store.

Disadvantages

The PVC tubing is heavy, flexible and slippery when wet, which is quite fun when going down wind with a bit of lee helm and the whole thing suddenly goes like a bow and you bear away suddenly.

Rating

Emergencies only

Version 2 The Fisherman

Version 2A Carp Landing

Difficulty – low to slight

Go to your local fishing emporium and ask for a one piece carbon carp landing rod. Remove the heavy steel thread from the end and insert the universal joint, pack to fit and secure with a screw or bolt.

The carp landing rods are also available in two pieces; these can be made into one piece with the careful use of a fibreglass or carbon bandage over the joint.

Advantages

Very light weight and seem to be available at low cost. Approx £10-15

Disadvantages

If carp are not fished in your location you get some strange looks in the fishing tackle shop. They are extremely light weight but for the cost can not have much carbon in them and potentially a bit fragile, only time will tell

Rating

Fishy stories abound of an increase in shrimping or trawling the kite when in use

Version 2B - Fishing rod handle

Difficulty - Low to minimal

Instead of a carp landing net handle - a cheaper version is that of the carbon bottom sections of a fishing rod. Usually found in any “half decent” fisher-ing-stylee shop. These can be sourced at around 6ft & very stiff with often a very fancy carbon weave on display. When fallen on they dont break, & can be obtained for around £5 each as most people tend to snap the tips - so the shops sell these and are left with bulk 'rubbish' which they are more than happy to flog on. Just strip off the metal reel bracket & Bobs your uncle!

Advantages

Very quick and easy to attatch UV joint as the thin end is often exactly the right size, and its a nice diameter rod to hold onto. & if your lucky, you may be able to lay your hands on a fine rod, such as “the COD father”!

Disadvantages

Much micky-taking of the rod, and utter jealousy from tin stick holders.

Rating

8/10 Even to carry as a cheap spare - its ideal!

Version 3 The Gardner

Difficulty - low

All you need is a bamboo garden cane, a short length of hose pipe and cup of boiling water. Select the garden cane and cut to length so that one end is slightly thicker than the inside of the garden hose. Cut a 10-12cm length of garden hose and place in the cup of boiling water. This will soften the hose and make it expand a bit. Once it is soft push the Universal Joint and the end of the cane into the hose so that they butt up against each other. When the hose cools it will contract and hold the UJ tight on to the end of the cane. For extra security a screw or bolt can be used. The joint between the hose and the UJ is a bit flexible and can give control problems when right at the back going down wind; however this can be improved by taping a short length of batten along the joint as a stiffener. If you were being really trick you could make a glass sleave.

Advantages

Very low cost bamboo cane is available from about £2.50 for a pack of 10 Garden hose is also cheap especially if you just shorten one that you already own. They are light and can take a lot of abuse good ones will just spring back to shape if you land on them.

Disadvantages

They are a bit flexible and slippery and if you get a bad one it will not last long. Rot is also a problem and will get even the best cane in the end. You might get a slagging for bringing the class into disrepute with new levels of sailing a boat made from junk.

Rating

Visiting garden centers may lead you into more sedate hobbies, when do you plant bulbs?

Version 4 The Professional

Difficulty – Very low

Just buy from a shop! It will come ready to work you just need to attach it to your boat they come ready with built in grip and great names like battlestik and carborod.

Advantages

You do not need to do anything but fix it to your boat

Disadvantages

They cost anything from £50 to £100 and the high end carbon ones are so strong that falling on them is more likely to snap your boat than the tiller extension.

Rating

A bit too flash, may lead to being ostracised from the Cherub class for blatantly buying part of your boat from a shop.

Version 5 Build from scratch

Difficulty – medium to high

Rather than buy or convert something into a tiller extension you can always build the whole thing yourself Described below is one way of making a tiller extension, there are others and they may well be better. You will need a mandrel, wax, epoxy and glass or carbon. Get a length of 22mm diameter copper pipe and coat liberally with wax, this is best done with a brush and the wax melted in a pot on the stove. Making sure that every part of the pipe is covered in wax is important as you want to be able to get the pipe out at the end. The tube is made from a layer of braided glass sock followed by a layer of 300gsm unidirectional carbon fibre and an outer layer of glass/Kevlar sock.

The braided sock is great for this sort of application as it can be expanded to thread over the tube and when pulled tight will shrink down to a neat snug fit with no seams. There did not seem to be much difference in difficulty between wetting out the sock on the tube and wetting out on the bench and feeding it over the tube when wet. Both methods were messy and sticky and the ease of use seemed to depend on the make up of the sock used. One type was easy to handle when wet and the other was a pain. With everything wet out and assembled the whole thing was wrapped as tightly as possible in peel ply to consolidate it and squeeze out some of the excess resin. Once the resin has cured the copper pipe can be filled with hot water to melt out the wax, when the wax is soft it is easy to slide the new tube off the pipe and remove the peel-ply.

Then just fit your UJ and attach to the boat ready for sailing.

Advantages

As light/stiff and strong as you want to make it just add extra layers in the build if you want it to be a bit tougher. The peel-ply leaves a textured finish which is good for grip. Cost is from about £15 depending on how much carbon you use. The satisfaction of having done it yourself

Disadvantages

It takes a bit of time and preparation to build plus it is easy to make a mistake and ruin the whole thing. You do need to get all the materials and have access to somewhere that you do not mind getting messy.

Note

A bit of work may be needed on the specification after one of them broke first time out.

Rating

Acolyte, you are now starting the journey to become a cherub guru. If you make the UJ yourself you will achieve the rank of guru.

Version 6 - The High Flyer

Difficulty - Medium

Carbon Kite Rods are availible from many online kite shops with 2m long 16mm diameter tube availible for approx 30 Euro on at least one side of the channel There are a little bit thick but it's OK and you can improve with a little grip at the bottom end

Advantages

It gives popping the Kite a whole new meaning and you will really fly down wind.

Disadvantages

You may need to brush up on your GCSE French to order.

Rating

très bon

Version 7 The Sailmaker

Difficulty - low

Take the broken stub of your tiller extension and a long sail batten. Apply vast amounts of ductape to bond them together in a 'splint' fashion with the flat end on the batten towards the joint. Sail Away.

Advantages

You probibly have a sail batten somewhere anyway and if you dont have ductape someone else will so ideal for those emergancy brakage occasions.

Disadvantages

Next to no grip and extremely flexible. Ok in no wind, dont bother in more than a F2. Due to being so flexible they also have a tendancy to literaly tie themselves up with anything in their near vicinity: mainsheet, toestraps (what are you doing with toestraps anyway?) and even under the rudderblade at times.

Rating

Emergencies only, if that.

Building a Trailer

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Building a Trailer

Boat trailers are not cheap and it is all too easy to forget about the cost of one when costing up a boat build. However, with the right skills and tools you can save a large sum of money over the cost of buying a new trailer by doing things yourself. This page shows the re-build of an old trailer that once belonged to Flat Stanley. Although, so little of the old trailer was servicable that this should give enough information for a new trailer build.

Disclaimer

The methods we used to repair the trailer are outlined below, they may or may not work for you, involve the use of dangerous equipment and failure while driving is very serious, if you intend copying any of the techniques used please ensure that you understand all the risks involved.

Salvage what you can!

When we started, this old trailer was barely a trailer at all. The tow hitch was solid, as was the main beam which runs along the trailer length as well as the the mast crutch and bow support. The wheel bearings were shot and the rear crossmember and suspension was corroded so badly that it took on the appearance and structural propeties of puff pastry when hit with a hammer. So out came the grinder and we got to work.

The bits we saved were:

The main beam (this runs the length of the trailer and has other parts attached).
- Tow Hitch
- Mast Crutch
- Bow Support
- Front Cradle
The flat tie beams (these triangulate the join and keep the trailer square).
Mud guard brackets.
Wheels.
U-Bolts (some of these got destroyed by the grinder and were replaced).

Tow hitch on main beam:

Get Supplys

The bits we need to make a functioning trailer were:

Bearing/Suspension units (the light duty ones we found were rated at 350Kg, a little heavy duty for a Cherub trailer but will do the job).
Rear cross member (we purchased one ready made which is fine for us as we did not want a combi style trailer but if you want yours to be combi style you will need to make one as the pre-made ones for the light weight wheel hubs/suspensions only come in a narrow format. Fine for just a boat but too narrow for a boat and trolley).
Mud guards.
Assorted nuts and bolts.

These can all be sourced from Towsure.

Head for the Shed

Once you have your parts you will need to get hold of a welder. We used an arc welder as it is easy to use and does not require gas bottles. You will probably need something like 100A current for this kind of work. If you are new to welding then get some practice first with some scrap metal. Weld a tab onto the center of your cross member, this is what your u-bolts will clamp on to so it has to be substantial. We also welded the flats of the u-bolts onto this for good measure. You will then need to weld some rings onto your crossmember for strapping the boat down. Again, these need to be strong for obvious reasons!

This shows the flange and the u-bolt flats all welded up:

This shows the rings for strapping the boat down:

That is all the welding done. Unless you need to make mud guard brackets. The next thing to do is to bolt your cross member to your main beam with two u-bolts. Then add your flat tie beams (traiangulation struts). These are fixed with a single u-bolt and the front end and the rear end is fixed when the suspension units are bolted on. Then either make, buy or salvage some mud guard brackets and bolt the whole lot together with your suspension units and cross member. Bolt your mud guards on and the jobs a good-un!

Cross member attached to main beam with two u-bolts:

Front of flat tie beams attached to main beam with u-bolt:

Rear cross member showing suspension unit, mud guard bracket, flat tie beam attachment and tie down ring:

Put the wheels on and you have a trailer. Now all that is left to do is to add a cradle or trolley supports and give it a coat of paint. Red-oxide primer and Hammerite should do the trick.

Schoolboy error!

After finishing the trailer it came to my attention that I had forgotten post 97' boats have a 30cm 'snout'. This meant that the bow support had to be moved to allow for the snout to sit behind the mast crutch. The old bow support was simply cut off and welded on to a bit of 50mm box 300mm further back. The whole assembly sits just shy of 200mm above the main beam.

Cradle

There are as many ways of doing this as there are Cherubs but I thought I would add a little note as to how I did it for reference. The cradle is made of several layers of 4mm exterior ply laminated together with support at each end and a large weight in the middle. This is then secured to the supports with four coach bolts. Coach bolts are used as they have a shallow, round head which wount stick through the trailer padding. You could use counter-sunk bolts for the same reasons, which may be neater.

Vacuum Bagging

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Vacuum Bagging

Vacuum Bagging is a technique used to reduce the weight and increase the strength of composite panels. When laminating any voids, air pockets dry patches or areas with excess resin will act as weak spots in the structure, by consolidating the laminate while it is curing these problems can be reduced and a stronger laminate stack will result. It is possible to build the laminate lighter as due to the extra strength you could use less material. Typically when wetting out too much resin will be used so as to avoid dry spots, when consolidating with vacuum pressure it is possible to use a cloth to absorb the excess resin which is then removed, leaving a lighter more consistent structure.

Atmospheric pressure normally acts on all sides of an object so it is often ignored, however by removing the air from the bag the atmospheric pressure will only press against the outside of the bag forcing it against the laminate with the weight of the atmosphere. One atmosphere is 14.7 pounds per square inch or 1.033 Kg Force per square centimetre. So if you could pull a perfect vacuum you would have the equivalent of a bag of sugar pressing against each square centimetre of the laminate while it is curing, something that would be difficult to achieve with clamping over a large area. In practice you are only likely to get a differential pressure of 0.7 to 0.8 of a bar but that would still be 700 to 800 grams per square centimetre which is quite significant. If you want to get more than that you have to get quite high tech and increase the pressure outside the bag, this is done by putting the laminate in a pressurised autoclave with the bag venting to the outside, not something to be found in most garages.

One of the most important things to get right is the sealing of the bag, any leaks will mean that full pressure is not achieved and if the leak is in such a place that air is pulled through the laminate then the part will be ruined. The bag can be sealed round the edge of an airtight mould or it can be used to completely encompass the piece if you are working on something small. It is also important to ensure that the bag does not bridge any sections of the mould, on a flat surface or convex shape this is easy but on a concave shape you need to be careful to ensure that there is enough slack in the bag to go into all the corners and that excess bag material is bundled up into pleats with all edges sealed.

Equipment

Vacuum Pump
Vacuum Bag
Tube from pump to bag
Tacky Tape – Very sticky putty that is supplied in a roll of tape it sticks the bag to itself and to the mould you are working on
Breather Fabric – A soft absorbent material much like a blanket, it provides a path for the air to escape to the vacuum port and will absorb any excess resin.
Bleed Film – A thin plastic film with loads of small perforations through it, it allows the air and the resin to escape from the laminate stack to the breather fabric, it also makes it easy to remove the breather fabric from the laminate.
Peel Ply – Provides a good surface texture for future bonding and provides an extra path for the resin to escape the laminate stack.
Vacuum port – this can be as simple as pushing the hose into the bag surrounded by tacky tape or a specific port that clamps onto the bag and has a connector for the hose

Optionally you can add

Resin Trap – Placed in the line between the laminate and the vacuum pump, it will prevent any resin that enters the vacuum tube from reaching the pump and destroying it.
Vacuum Gauge – Can be placed on the bag away from the vacuum port so you can check that you are getting good pressure across the entire bag.
Non Return Valve – Stops air from entering the bag if the pump stops.
Stethoscope – Used to listen to the bag and locate leaks

An Example Laminating a hull

The mould should be built with a flange around the edge to stick the bag to and should be made from quite a thick laminate to try and ensure that there were no leaks through the mould structure itself. While we were wetting out the hull we protected the flange using masking tape so that we could remove any resin that dripped on to it.

The cloth was wetted out as normal and then a layer of peelply placed over the top, followed by the bleed film. The bleed film was tricky to place as it is quite slippery and it was difficult to keep it in place on the vertical sides of the hull. Corners were also difficult as we felt we needed to avoid having several layers on top of each other which might block the flow or air and resin. With the Bleed film held in place with some masking tape the bleeder cloth was added over the top, ensuring that we had an extra layer under where we were planning the vacuum port and running the length of the hull to provide a path for the air to escape. The masking tape around the flange was then removed and tacky tape stuck down ready for the bag. When fitting the bag big pleats were needed at the bow and around the transom to allow the bag to conform to the contours of the hull. Where you have a sharp internal corner like a chine and the bag or any of the other layers are too tight it can bridge the corner and you do not get pressure in the corner. To avoid this the vacuum was pulled and released a few times allowing the layers to be moved about through the bag till everything was in the right place.

Vacuum Infusion

In Vacuum Infusion rather than use the vacuum to consolidate an already resin soaked laminate the dry cloth is placed in a mould, and the bag fitted and vacuum pulled. A port is then opened and resin flows in to the laminate. It looks like it is being sucked in to the laminate but it is actually pushed by atmospheric pressure.

The advantages of this are that you have unlimited time to position your reinforcement material, without being hurried by the resin cure time. The exposure to the resin is smaller as all you have to do is mix it and put it into a tub with a tube in it. The minimum amount of resin is used as it will only flow into the voids between the layers and there will be no pockets of air in the laminate. This tends to be more of an industrial process as controlling the flow of the resin to ensure that it gets to every corner can be tricky in a complex shape. To get the resin to flow you need an additional flow media as well as some additional pipe work to deliver the resin. Any holes or leaks in the bag will totally ruin the part.

Video

Gavin Sims, Simon Goodwin and Simon Turnbull have been busy in Wales doing bits for Mango Jam (2682) and Strangely Brown (2651). They did the vac-bagging and took the photographs, and Daryl Wilkinson made the video

Repairing a wooden hull

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Repairing a wooden hull

The holes were created by an unscheduled stop on some piles aided by the Exmouth tide!

Repairing the first hole

The first thing that Ed Higham and Francis Screech did was to make the holes a regular shape, this would make repairing it a bit easier to do.

Whilst Francis was getting on with making the shapes regular, Ed insted of beaing lazy and watching, decided it was a good idea to cut the wood out the right size to fit the holes!! (note: it was marine ply)

After Francis had made the holes regular, he decided to make the sides as smooth as possible, he did this by using fine sand paper!! (note: used fine sand paper to get the smoothest edge)

Repairing the second hole

With the second hole francis repeated the way he did the other hole but on a much larger scale.

We Then worked from the top hole and stuck battens across the inside of the tank so they would provide stiffness and shape to the chine. On top of the battens we expoxied on a piece of marine ply exactly the right dimensions and waited for it to set. Using fibreglass tape and resin, we sealed all around the join INSIDE of the boat so we did'nt disturb the hull shape at all.

The top hole was slightly harder to work at becuase there was no access hole so we stuck a frame around the inside of the hole which after was covered in silicone sealanta, then placed on a perfectly sized piece of ply. The idea was that the silicone would squeeze out and seal the gap. With no visible sign of silicone, we decided to use marine filler over the top of the repair which we knew would sand down afterwards. We did this, primed it, then painted it.

So far the bottom hole seems watertight which is a huge relief as this repair is the first big job we had ever done and was a huuuge hole! Sadly the top hole failed after a speedy jump out onto the wire resulted in it becoming cracked. We didnt think there was any way of making an 'invisible' repair strong enough so we fibreglassed over the repair and then put a patch on top to get us sailing again. Even after a windy day, all repairs have survived and only a dribble of water came out, woo! Now that was a good deal!! (and no holes in our walets)

Wooden Boat Repair

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Wooden Boat Repair

There are a large number of wooden boats about, many of which need a bit of repair.

One example is the repair to 2539 following an encounter with a piling while sailing.

Building your own Ply/Glass Cherub.

anonymous@undisclosed.example.com (Anonymous) — Wed, 09 Dec 2020 19:22:00 +0000

Building your own Ply/Glass Cherub.

Disclaimer This document is compiled by an amateur, not a professional. It has been compiled in good faith, but almost certainly contains errors and inaccuracies. “Best practice” also changes frequently with changes in technology and materials. None of the procedures listed are guaranteed to work, and some or all of them may be hazardous. If you feel unable to take responsibility for your own actions and errors without resorting to the legal profession then you are advised not to read it, let alone build anything based on information here. In any case you are advised not to build a ply/fibre boat without someone experienced in the materials to contact for advice.

Introduction.

These days foam sandwich is the popular option for the home builder of Cherubs. It is probably the easier material to work in and gives a low maintenance boat. On the other hand wood is still a nice material to work with and does produce a really pretty boat if you get it right! A wooden boat built in the hi-tech manner described here, which is some way removed from traditional boatbuilding, will also be a little more proof against knocks and dents than a foam boat. This is intended as a selection of hints about Cherub building in particular, not a complete “how to”. There are many books available in shops and from libraries that will give you most of what you need. Other good sources of information are the suppliers of boat building materials. Traditionally Cherubs were built out of Aerolite 306 or Aerodux. These still work fine for all wood boats, but the techniques are very different to those described here, and weight is a major problem with this sort of construction. The best wood boats before fibre/reinforced plywood became used were probably the cold moulded ones, either fully or just the area below the chines.

Home building is usually a rewarding process. A mixture of blind determination and some skill in handling tools is important, although enough determination and patience can make up for a shortage of skill! Probably the most discouraging factor is the air of mystery that surrounds boatbuilding. Just remember that skilled traditional boat building is an arcane and complex art that has almost nothing in common with building a modern Cherub! I suppose it has to be conceded that the Cherub, being a very light boat with considerable performance and very high stresses, demands careful consideration in the building process. It means among other things careful assessment of materials, quality of jointing, use of suitable adhesives, and above all finding out what other people have done successfully - and unsuccessfully in the past. There is no substitute for talking to other people who have built new boats or owned second-hand boats. The class association will always be happy to put you into contact with people who have had considerable experience of wooden construction. Fortunately Cherub sailors tend to be a friendly and open bunch, and are always ready to help with genuine enquiries.

Design.

There are a great many designs of Cherub. Most recent designs were designed for foam sandwich, so you may be a bit on your own working out details of bulkheads etc. However the designer will always be happy to make suggestions, and most have enough experience of wooden boats to be able to give you some extra information in exchange for their design royalty. In selecting a design it is best to talk to others in the class. At any given time there is usually a dominant design that is a safe bet, and they can give you advice on what suits your crew weight or sailing area.

Preparation.

Having selected your design and bought your drawings you will have, at best, a large selection of drawings, a table of offsets, a selection of detail sketches, and a list of suggested materials. At worst you'll just get a series of scale drawings and sections. If you don't have a table of offsets you will have to cross check regularly as temperature and humidity changes can distort drawings. The aim is to get as fair a hull shape as possible and one as near to the designer's intentions as possible. You will need to end up with a set of formers no more than 18“ apart (12” near the bow), set on a rigid foundation if you are to produce a fair and symmetrical hull. There are two ways of doing this. Firstly you can trust to luck, make the formers to the shapes given and, once it is all set up, fill in the dips and pare down the bumps that will almost inevitably appear when sighting from various directions. This sometimes works well, especially when you are on your 5th or 6th boat and have had some practice! It can also be a bit risky if some of your measurements - notably rise of floor - are near the limits before you start paring! The second method is to 'loft' the lines, which is basically drawing them out full size (emulsion painted sheets of hardboard are good), having drawn an accurate grid of station and water lines on which to plot the offsets. If you don't have a table of offsets you can scale them from the drawings, although this is tedious and it is easy to make mistakes. The great advantage of lofting is that by referring back and forth between elevations and plan you iron out bumps and hollows and can easily check that measurements are within the limits allowed. Another benefit is that many of the construction details can be plotted and the details taken off by paper patterns. For information about lofting refer to 'Complete Amateur Boat building' by Michael Verney (pub. John Murray) and 'Boat Building' by Howard Chapelle (pub. Allen & Unwin). Don't refer to them too much for constructional details though!

Recommended materials.

Hull floor

4mm ply. 60g kevlar or 105g glass coating on the inside, 105g glass on the outside skin.

Topsides, decks, bulkheads, daggercase sides etc.

3mm ply all the ply should have a layer of 105 g glass or 60g kevlar on the inside. Use lightweight Gaboon ply (hardwood veneered looks ery nice but can be a bit heavy). Nowadays by far the best source is Israeli made WBP gaboon, which is light, strong and very cheap.

Stringers, stem, other strip wood.

Western Red Cedar is favourite. It splits very easily, and needs to be coated from ply surface to ply surface with glass.

'Decorative' stripwood - Gunwhales etc.

Spruce or mahogany. Spruce is lighter, mahogany is more durable, but can be very heavy. At the most a thin capping is all you should use. Really good clear pine may be almost as light as spruce and is easier to get hold of. Getting suitable wood can be a problem, and be very careful about adding weight. If you are not worried about getting a Grand Piano appearance then use cedar and glass coat it. Some people have even used balsa wood coated in glass for glass coated stripwood, but of course in this case the wood is doing no useful work, and serious quantities of balsa wood get very expensive.

Building jig.

Formers are best made from something like 3/8“ building grade plywood. Slightly damaged sheets can often be got cheaper. Strip wood can be anything that's reasonably solid and cheap. If you're using second-hand wood make sure you get every nail out!

Glues.

Use Epoxies. SP320 is the best for the sort of fibre re-inforced ply construction we are talking about here, SP106 or West 105 are cheaper.

Tools.

A staple gun is essential for fastening plywood down. It is cheaper and lighter to tack down with staples and remove them afterwards than to use expensive marine-grade fasteners and leave them in. Otherwise normal carpentry tools are fine, but you can never have enough G cramps. If you have less than about 15 get borrowing!

Construction.

Advice is always helpful, but make sure you understand it completely! Be a bit careful of people who have built 5 Enterprises. They will probably tell you that such and such a bit has to be that thick or glued on that way. It may well end up too heavy and not strong enough! If advice does not seem to add up pay attention to your own inner murmurings. One excellent piece of advice is to have a comfortable 'thinking chair' in which you can put your feet up with a cup of tea - or something else relaxing - and look and think hard about the current problem. Thinking time is rarely wasted - especially if it means you don't have to do something twice!

Cherub Specifics.

I will assume that you are building a self draining boat, to be quite honest if you don't you will curse yourself when you start sailing it!

Ply joints.

Any place where two bits of ply join at an angle needs a generous lightweight fillet, preferably with glass reinforcement running 1” or more from either side of the join. Beware weight. Use the lightest possible filler. The glass over the join should be cut on the bias at 45 degrees - it will go round corners more easily and is twice as strong.

Bulkheads.

Wooden boats are like banana skins. The longitudinal seams will split open unless they are sufficiently braced across the join. This is mainly achieved by transverse bulkheads. Locate these about halfway between the mast and the bow, under the mast, at the rear of the daggerboard case, under the mainsheet position, and between the mainsheet and the transom. The transom itself forms the final bulkhead. This one needs to be 6mm wherever rudder fittings will attach, and really solidly glassed in. Cherubs are notorious for rudder fitting problems. It is better to have a smallish drain vent in the transom rather than a completely open one, both for strength and for sailing. A longitudinal bulkhead will run from bow to stern. Don't forget to arrange for the minimum 3 buoyancy tanks.

Outer Skin.

Absolutely vital is a really good join at the centerline and chines on the outer skin. Some people cold-mould the bottom out of thin ply strips, and this gives a really strong boat if you have the time and skill. In the days before false floors two layers of 3mm ply for the bottom skin were recommended, and in this case the joints were staggered. A single of 4mm ply is recommended. A lot of modern designs are very flat floored, and it might be possible to get away with a single sheet, but this will very much depend on the amount of rocker. Normally you will need a joint in the middle. For the reinforcement you could put stringers on the inside, (and in any case one light stringer will probably be needed to keep the profile correct), but a much better way of stiffening up and supporting the outer skin is run the inside fibre coating over epoxy fillets onto the hog and chines. This provides a really good support with a minimum of hard spots. The hull skin should also be glass coated on the outside, and this should be done last of all, running from the underside of one gunwale to the other. You will need to scarph joint two pieces of wood for the bottom panels as twelve foot 6“ lengths of marine ply are rarely available, and this is best done on a flat surface before putting the panels on the boat. You may well find that vertical strips need to be cut in the skin on the centre line near the bow because of double curvature. If you have a really complex shape you can make it up from all sorts of odds and bits. In any case, once the boat has been turned up, you will need to add a lot of stiffness in this area, which takes a real pounding going upwind in a chop. Probably the most suitable method is to use two layers of uni-directional carbon criss-crossed diagonally from chine to hog, and then a layer of glass over that. Try to fillet and shape the hog to let the glass go in one piece from chine to chine. This area used to be a common point of failure in the old days, and is one where the use of modern materials really pays off. Extend this extra reinforcement to about six inches behind the daggerboard case. The glass coating needs to be made with a very low resin to glass ratio. Beware of adding weight! The way to achieve this is to use a heat gun to warm up the resin and a roller to really spread it out. Don't be tempted to warm up your pot full of epoxy though, it will go off in no time at all, leaving you with a beautifully moulded epoxy casting! It is wise to keep your resin in a tray once it is mixed as it will not go off as quickly.

Mast support & Space Frame.

This is an important issue. With the sort of rig tension used these days the peak loads going down the mast probably approach tons! Exactly how you step the mast is up to you, but the favourite location is on the false floor. It is conventional to support the mast with a space frame. This is not the sort of alloy contraption you find on some boats, but a ply/carbon/strip wood construction integrated with the main bulkheads in this area. Longitudinally it runs from the keel under the mast up to the top of the bow, from there up to the prodder anchor point, back down to the mast foot, and from the mast foot back down to the hog. Maybe also back to the post. Laterally it goes from the mast foot and the hog out to the shroud anchorage points, the front bulkhead being angled back on both sides. Arrange it so that the mast sits on the crossing point of the longitudinal and transverse bulkheads. You will need a really strong point for the prodder. It is advisable to have a foredeck on a wooden boat as it does a lot to stiffen up the front of the boat and support the rig loads. The basis for the prodder support can be the beam down the middle of the foredeck, which meets the upward extension of the space frame. Put a transverse bulkhead across too, but make it very light as it will take very little load (except when the crew crawls across the foredeck to disentangle the kite. The bulkhead supporting the foredeck will also be angled, but should run from the shrouds to just in front of the mast. With the typical Cherub rig of lower shrouds and prodder you will not need to support the mast at deck level, but you might want to put a bit of strength there in case fashions change.

Daggerboard case.

Fortunately the false floor does a lot of the support for the daggerboard case. If you have a stringer each side of the daggerboard case to support the false floor they can support the sides of the daggerboard case. You may well want to bring the daggerboard case up a bit higher as the foundation of a tunnel. This keeps control lines out of the way, and gets the bowsprit out of the way when retracted, and can be used to stow the kite. The tunnel is probably best made from two layers of 3mm ply to give stiffness.

False floor.

You will have a variety of bulkheads to mount the false floor on as detailed before. Naturally all those which are not required to be watertight will be reduced to webs. These should have slim battens mounted on the top. You should also have stringers running down in the main stamping area. Work out exactly where the battens etc. are going to run, and put an extra layer of glass on the underside extending 25mm each side of where the bulkhead will touch. This will reduce the hard spot considerably. The floor should be 3mm ply with a layer of 100g kevlar on the underside. On the topside put a layer of 105g glass, and run it up over the fillet where the sidetank joins. This will stiffen it up, add wear resistance, give you a non-slip surface, and make holes much more unlikely. While on the subject of false floors, you will no doubt need hatches in them, but never put them where they can be stepped on. The hatch causes a hard spot which will crack. Right in front of the transom is a good place, and it also gives good access to bolt on rudder fittings.

Side tanks

If you have a reasonably deep false floor you can probably do without side tanks. However I would still advise side decks as they stiffen up the gunwales so much. The join between tank side and floor is a common point of failure, give it a good fillet and glass reinforcement. You may as well have some kind of side tank , because the box section gives so much extra stiffness, but you may well want to run sheets and things through forward.

Time.

Probably 200 hours or so with experience, and maybe approaching 300 for the first time builder. Cost of materials depends vastly on what you use and where you can get it. As of 1991 you would probably spend between UK£300 and UK£600 pounds on the hull, which is appreciably cheaper than foam sandwich. Finally - don't forget: If in doubt - think. If still in doubt, ask a few people and think again. “Think twice and cut once is a very appropriate maxim. Have fun!

Jim Champ, adapted from Dick Jarrett. Andy Paterson of Bloodaxe Boats, who is by far the most experienced builder of glass/ply Cherubs gave me a great deal of help in preparing this piece, in particular in the choice of materials and other details of fibre-ply sandwich construction. Photos © Bloodaxe Boats, Jim Champ, Bloodaxe Boats.

If you wish to have fuller construction details for building a ply sandwich boat then it would be worth considering purchasing a set of plans from Bloodaxe Boats, which contain much more detail than is practical to include here.

If you would like details on the methods traditionally used to construct ply Cherubs then the best source I am aware of are the drawings & construction plans for Farr Design #48 from Farr Yacht Design Ltd.

UK Cherub - tech

Adding a snout to an Italian Bistro

Adding a snout to an Italian Bistro

Anti Bruise Technology

Anti Bruise Technology

1) Decide not to sail again until boat does not destroy knees

2) Buy a garage

3) Buy Pro-grip

4) Make garage fit the boat

5) Remove interior

6) Reinforce back of castle

7) Apply pro grip

8) Touch up interior paint

9) Sail boat

Snouting

Snouting

Day 1, Hit 1

Day 2, Hit 2

Day 3, Hit 3

Day 4, Hit 4

Day 5, Hit 5

Day 7, Hit 6

Day 8, Hit 7

Day 9, Hit 7

Day 10, Hit -

Day 11, Hit -

Day 12, Hit 8

Day 13, Hit 9

Day 14, Hit 10

Day 15, Hit 11

Velocipide 2675 Build

Velocipide 2675 Build

Building 2676 Shiny Beast

Building 2676 Shiny Beast

AquaMarina Build Photos

AquaMarina Build Photos

Building a Single Skin Rotating Gantry

Building a Single Skin Rotating Gantry

The Shape

Building the Mould

Building the Gantry

Pictures

Lessons Learned

Further Reading

The build of 2684

The build of 2684

2684 The first US Cherub

2684 The first US Cherub

Exultant Jubilation - The Build

Exultant Jubilation - The Build

The end of the build Sept 2009

A Little less conversation...

...A little more action

What went into the boat - Cookbook

Hull

Skin

Deck

Bulkheads

Mast Bottom Section

Mandrel

Hit 1

Hit 2

Mast tip

Mandrel 1

Hit 1

Hit 2

Hit 3

Mandrel 2

Spreaders

Racks

Mast stump

Rack supports front

Rack supports rear

Tension Struts

fixing a bent aluminium mast

fixing a bent aluminium mast

Boat Amnesty

Boat Amnesty

Natural Born Skiffers

Atum Bom