UK-Cherub Forum

Cherub Chat => Tech Chat => Topic started by: ade white on January 11, 2013, 05:36:36 PM

Title: Sail Design. Masthead/batten.
Post by: ade white on January 11, 2013, 05:36:36 PM
I am currently re-making one of my old sails. this is the mainsail i used at this years inlands and measures 8.5m approx. Although old it is still fast! The re-make will take it to 11.5m, but will it be any faster? This should give me the max size area for 05 rules. I am hoping to stop using the excuse "they have bigger sails than us Joe, so its ok if they are going faster."
So 'big is beautiful' in my eyes and although it will look like 'Nora Batties stockings', I am hoping to test whether I can go faster upwind (under F2 conditions...I sense a lightwind season is ahead).
In my re-make, I am thinking about redesigning the top of the mast to incororate a swivel attachment just above the halyard tieoff. This swivel will be the housing for the top batten. the top of the sail will be the batten. therefore the top of the sail will have no/very little downhaul pressure but still be tensioned on the leech. Can anyone think that this may infringe any rules? the sail top will be more than the square tops and similar to the 18's...
After looking at the 18 rigs and the top of their sails, there is a lot going on, lots of different ideas. On some of these rigs much seems to be wasted even though the twist still looks good. I remember we tried lots of different ideas on windsurfing rigs in the past and, although a different concept, 'floppy- flappy' leeches worked really well, but were only controllable on the massive downhaul tensions and mast stiffness.
I dont intend it being 'floppy-flappy, but, I think I could gain more power/control/speed from the sail being able to rotate and tensioned from the leech via kicker adjustment. At present, i think, we rely on mast/downhaul/kicker but with no rotation. I am thinking also that it may relieve some of batten popping problems we all suffer as well. It could make worse though but i dont see how?
Any comments gratefully received as to me plan before i cut me mast.
Title: Re: Sail Design. Masthead/batten.
Post by: Torchy on January 11, 2013, 05:49:12 PM
I am hoping to test whether I can go faster upwind (under F2 conditions...I sense a lightwind season is ahead).

I detect some wishful thinking Mr Light Airs Lightning

Haven't had a chance to test my 'easily adjustable upper batten theory' but auto-release of square top seems logical and there is a video on 18footerstv of (I think) Rag and Famish making a big rig work in 18kn (in that case a 'round top').

If I can trace it I'll post it.
Title: Re: Sail Design. Masthead/batten.
Post by: Torchy on January 11, 2013, 05:53:27 PM
I am thinking also that it may relieve some of batten popping problems we all suffer as well.

Be careful talking button popping problems...Hayley's lurking
Title: Re: Sail Design. Masthead/batten.
Post by: Hayley_Trim on January 12, 2013, 07:43:18 PM
Lurking eh? c'mon, batten popping aside, this is way too easy.

Although old it is still fast!
So 'big is beautiful'... in my ...'Nora Batties stockings',
I dont intend it being 'floppy-flappy, i think, we rely on... rotation.

(sorry Ade  ;) )But then Roland has just pointed out that we have spent the afternoon driving round searching for a pair of old ladies' drawers ...
Title: Re: Sail Design. Masthead/batten.
Post by: Torchy on January 12, 2013, 08:22:16 PM
If we keep bumping this post up Ade might get an answer
Title: Re: Sail Design. Masthead/batten.
Post by: MK on January 12, 2013, 09:59:44 PM
The ERS definition of spar is

Spar
The main structural part(s) of the rig, to, or from which sails are attached and/or supported.

So i would say that your attached part would be part of the spar meaning it is governed my these rules

4.2.1 Spars

The area of spars shall be considered as sail area. The area shall be taken as:-
               
Spar Area = (Spar chord – 100mm) * Spar Length
               
Where: spar chord = the diameter of the smallest circle through which the spar could be passed when stripped of all fittings.
               
If the spar chord < 100mm then the area shall be disregarded.

4.2.4 Upper Limit mark
               
The upper limit mark is to be placed on the mast so that the distance from the heel point of the mast to the upper limit mark plus the vertical distance from the mast step to the lowest point of the hull shall not exceed 7100mm.
               
4.2.5 Sail Height
               
The luff of the mainsail shall not be set above the upper limit mark on the mast. The lower edge of the spinnaker halyard shall not be above the upper limit mark on the mast when at 90O to the spar, each extended as necessary.

So in summary its fine, just dont put it above 7.1m from the bottom of the hull and if you make its section over 100mm it will be considered part of your area
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 12, 2013, 11:13:49 PM
Thanks Mk, from reading the information I think i am within the rules. The ring swivel design would incorporate a slot in section for the top mast head batten. As this is a removable, slot on fitting would it be considered as part of the mast and have to measure within the 100mm rule? I was planning on building a tube section onto the ring for the batten to push-fit into. The ring diameter is no more than 60mm and I could make the tube no more than 40 mm so I could make it that size, if dictated to.
I might need to make a couple anyway to test so is size an issue.
Title: Re: Sail Design. Masthead/batten.
Post by: MK on January 13, 2013, 01:08:56 AM
Because of the way you are using it to hold up the head of a quadrilateral sail the structural piece is a separate spar, technically a gaff

(v) GAFF
A spar attached at one end to a mast spar to set the peak, throat and/or head of a quadrilateral sail.

It is not a batten as it is attached to the mast spar

Your fitting should be fine, the intention of the rule is to measure in wing mast areas, or other aero type fairings
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 13, 2013, 04:11:05 PM
Thanks MK, Yes i guess it is a variation on the gaff rig, I had'nt thought of looking at it in that way, but i agree. As there is no cam system involved, (yet), it should be quite a simple mod. The thought of the gaff rig measurement rules and the idea that it is so old and outdated doesnt mean in the context, i am thinking it, is outdated and a silly idea. 

...shiver me timbers, cherub with a gaff rig... now that sounds mod!
...now waiting for them scallywagl pirates 'torchy' and 'hayley'...
Title: Re: Sail Design. Masthead/batten.
Post by: Phil Alderson on January 13, 2013, 07:45:33 PM

You might also need to watch out for:

4.3
SAILS
4.3.1
Material
The sails must be soft sails that can be stowed in sail bags of normal dimensions with
battens fitted (for the purpose of this rule, 'long' sail bags for the stowing of rolled up sails are
regarded as normal).

Title: Re: Sail Design. Masthead/batten.
Post by: Torchy on January 13, 2013, 07:46:53 PM
Arr Jim Laad!...I'm having trouble with me old gaff me-self...keeps sticking straight up when it should be at an angle...I think I be developin' a gunter rig.
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 13, 2013, 10:01:34 PM
Re rule 4.3 and 4.3 1 no problem there...
Although, as MK has mentioned, I am thinking there maybe an infringment on the spar rules for the rig attachment. I can easily adapt the masthead pad on the sail either by an integral fit or a fitting attaching to the masthead pad. This will be the insert for the masthead batten  Therefore the design mod will be all part of the mainsail.
I dont think the 7.1 rule refers to the max height of sail? Therefore, I still think I am within rules if the sail is higher than the mast?
I think I will continue to make both fittings and bring along to the next measurement session.
(Essentially, in-case I have'nt explained it well enough, if you imagine a 'gooseneck' type fitting slotted onto the top of the mast)- is it legal??? If it is, then the attachment becomes part of the spar. The spar then would protrude higher than 7.1 height. hense the rule break).
Title: Re: Sail Design. Masthead/batten.
Post by: phil_kirk on January 14, 2013, 12:56:10 PM
Before seeing Maff post i was thinking that it sounds like a gaff.

It's amazing how things come back in fashion.  I suppose old ideas such as a Gaff may work better with the application of modern materials.  Now didn't the gaff go out of fasion because it was harder to control twist (because the kicker hadn't been invented) or for reducing weight aloft when masts could be made in one peice.

Oh, what about a flying jib, stay sail or a top sail Ade? :-)

I've just started reading Frank Bethwaites higher performance sailing and the pitcures of the 18 footers from a couple of hundred years ago were amazing.  They set 4 or 5 additional sails for the downwind legs including water sails which hung below the boom and spinnaker pole. 

good luck
Title: Re: Sail Design. Masthead/batten.
Post by: Phil Alderson on January 14, 2013, 01:30:17 PM
Other than for the spiniker halliard there are no rules about how sails are attached to spars, however the luff of the mainsail may not be set above the upper limit mark the terms in bold are defined terms in the ERS


Title: Re: Sail Design. Masthead/batten.
Post by: PaulClements on January 15, 2013, 01:13:26 PM
Hello. All very technical this Cherub Forum. I better get reading. On the subject of sails a flexi fat head can work well if leach tension and mast flexibility are matched to crew weight. Everything flexes a bit absorbing gusts and storing and giving back the energy without disrupting heeling moment too much. Watching Paul Coute sailing last weekend at Chew (from the shore due to shoulder injury) it struck me his rig and sails are the bench mark of system integration.

I have bought Shiny B as the prize at the end of long term pysio and need to sort the sails (all knackered and very old fashioned). Can't justify copying the bench mark so am trying to adapt a replica Rooster Musto skiff sail. It is the right size and arguably should work. The MPS sail and mast are very well matched allowing a lazy helm like me to just lay back on the wire and let the rig do all the work. we shall see...

PS anyone got some foils from a Moth or RS600 they want to loan. I fancy lashing up a fully foiling Cherub just for fun!! Rolland could test it in case it proved dangerous.
Title: Re: Sail Design. Masthead/batten.
Post by: Hayley_Trim on January 15, 2013, 02:06:38 PM
PS anyone got some foils from a Moth or RS600 they want to loan. I fancy lashing up a fully foiling Cherub just for fun!! Rolland could test it in case it proved dangerous.

Er, he can use someone other than his regular crew for the first trial!
Title: Re: Sail Design. Masthead/batten.
Post by: JP233 on January 15, 2013, 07:48:02 PM
PS anyone got some foils from a Moth or RS600 they want to loan. I fancy lashing up a fully foiling Cherub just for fun!! Rolland could test it in case it proved dangerous.

Funny, me and Digby were thinking of a foiling Cherub this weekend, we thought the Moth T foil wouldnt be too good, but the foiling 49er concept could be improved by replacing the 49er-bit with a Cherub and not having a cannard fin but using the normal Tfoil rudder to adjust pitch.

Not sure if this has been said or allowed, but why not make the gooseneck 'male' part on the gaff spar, then have a hole in the mast for it to sit in??

Thanks
Jamie
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 15, 2013, 09:53:51 PM
Thanks Jamie, that has immediately given me more ideas for developing the idea, and it might make it simpler for me to model the fittings.
So far I have a sail head fitting, a ring fitting, and a mast top swivel fitting. the male batten slots into all these as there is a female tube bonded onto each fitting. The fitting is only loaded from batten tension. Therefore the sail head forces will be neutral, compression forces on one side of the ring, and a shear leverage force on the masthead fitting.
I think it looks tempting to go for the sail-head fitting...
Title: Re: Sail Design. Masthead/batten.
Post by: JP233 on January 16, 2013, 04:56:03 PM
No worries, i'm quite intrigued by this, have you got any pictures or drawings?

Title: Re: Sail Design. Masthead/batten.
Post by: roland_trim on January 16, 2013, 05:04:00 PM
Sounds like this can be simplified into more of an "uber batten" than a gaff if the "gooseneck"/ring/fitting can simplified into a bit fabric in a slot on the mast?
Another way of describing this would be to bolt/rivet/glue a plate onto the sail where the batten end protector in the luff normally sits to spread the load and attach your female socket onto this plate?
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 16, 2013, 07:02:04 PM
Yes that is exactly how the idea is going.  Def 'uber' For my first test it is a patch sewn onto the head with a tube fitting sewn into a pocket. The tube is at an elevated angle for the mast head batten. The idea would be for the tube (batten) to finish directly above the outer part of the sail head eyelet patch so as not impend any twist but allow the rotation I am hoping to create at the top of the rig. There would still be no downhaul tension here to effect or induce shape. The batten, I am currently thinking is similar to an ordinary tapered round section but more flexible. The head shape being very curved and also with more area than current mainsails. Batten length approx 2 meters with a chord bend of 45+mm ish.
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 19, 2013, 06:33:35 PM
I have shown the attachment it is the drawing for the new main. The drawing shows the mast head batten sewn in tube stop insert just behind the headboard. approx angle of batten 45%

here is an interesting reply from my brother (i keep having to apologise as he sails a 'Nat 12' and is therefore to be considered 'still a virgin'!)
...should work from a sailing point of view, just how to get it there and hold it up.
I assume hoisted with boat flat. may need a line to support batten, but the batten could have a split end which goes around the head board in a way that stops the batten dropping.
headboard will need to rotate about the mast without popping the luff in way of the headboard out of the track so a gaff type approach would probably be better than a batten idea, headboard with a half tube to sit about the mast, in way of the head board the sail is not in the track, so just uses the halyard to hold the "headboard half tube" to the mast headboard half tube shapped at the botton edge to allow it to slide back down the mast
.
Title: Re: Sail Design. Masthead/batten.
Post by: Clive Everest on January 19, 2013, 10:56:35 PM
Hi Ade,
This looks interesting, however how do you see it being better than a more conventional top batten (gaff) arrangement.
I am worried that a few mm of movement at the base of the batten will be massively amplified at the tip, but if the batten was to start further down the mast you could still have the same head profile but it would be more tolerant of any inaccuracies.

Clive
Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 20, 2013, 09:02:02 PM
Hi Clive,
I see what you are saying there.
Further questions from me include... Is it less of a risk incorporating the batten pocket into the headboard?
Or are you thinking the design should have the batten running lower and more vertical to the luff before arcing to the leech but below the headboard?
My thinking is; (I have 5.9m from goose to mast tip) I can increase the height aspect of the rig; given that I can increase the area considerably.
To re-cap... I think the twist control will be benefitial as the head of the sail will be creating vertical 'tension' instead of initial tension being created by downhaul.
Am I right in believing we induce mastbend to create twist at the top? I am thinking this design idea might somewhat create a more even twist.
Title: Re: Sail Design. Masthead/batten.
Post by: PaulClements on January 21, 2013, 08:00:04 AM
There is a masthead utube video of a MPS that is enlightening. The top is alive, flexing and opening with every variation in the wind. Key however is how low drag it becomes as the mast flexes. It not only depowers but it does not hold you back when it depowers. Richard stenhouse was best at achieving this go fast setup. Stiff bottom mast section, loads of cunni then chase up with kicker to get desired twist. The top quarter of the mast bends till the top batterns are nearly straight making the leach unstable. In a gust the extra pressure on the leach just opens the top of the sail, depowering and adding almost no drag. An unusual sideproduct of this setup is that sheeting the main in harder overbends the mast and power deminishes . Sheet out and the power increases. Tricky.

The MPS has no uppers but I guess the principle is achievable with the Cherub. Remember if the leach is set soft when windy it is important that the unused sail area goes low drag.
Title: Re: Sail Design. Masthead/batten.
Post by: phil_kirk on January 21, 2013, 01:00:31 PM
A well set up cherub rig should work in the same way.  The uppers have some effect but using cunningham should enable the top mast to bend aft and hence allow the sail to twist off.  If the uppers are softer this effect will happen earlier than with very tight uppers.

Just a little detail on the gaff arangement. If the headboard/gaff is set on a half tube that rotates round the mast the headboard will not be inline with the rest of the luff in the luff track on the aft edge of the mast.  This may cause wear to the luff of the sail or the mast track. 
This affect would be avoided if the headboard rotated around a point at the aft edge of the mast.  It is sort of like having a boom and gnav arrangement at the top of the sail.  Marmite's top batten tip is higher than the top of the mainsail luff. 

Title: Re: Sail Design. Masthead/batten.
Post by: ade white on January 30, 2013, 09:53:25 PM
It looks as if i maybe infringed rules on the first attachment.
I have now posted one of the other idea developments. The headboard can be tension-ed independently from a lower eyelet that has now become the attachment to the top of the mast. A down-haul tension can be applied to the headboard for adjustment. In between is a cam batten and the batten is allowed to bend vertically as well as laterally to control the shape.
I think it may sound a bit fiddly however It is only 1 adjustment and can easily be worked on a flat side cleat system. This could give me the same control and area i am hoping to achieve... further food for thought!