Author Topic: Everest 1 Cherub  (Read 20552 times)

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Offline Clive Everest

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Everest 1 Cherub
« on: October 03, 2012, 08:51:48 AM »
As anyone who could tolerate listening to me at the Nationals will know I have been planning a new build.

I did not want to start a forum topic until it was actually under way, which it now is:
I am posting as I know that I will get a lot of helpful hints on lessons others have already learnt,
I suspect that a few will be interested in what we are doing, and hopefully I can inspire others to follow or join this project.

I felt after a year sailing Cherubs that the new boats are markedly quicker than our old slug but also a lot harder to sail.
Whilst this was too our advantage at the nationals it was fairly unique conditions and we wanted a new boat for next year that was closer in speed to the latest boats whilst trying to make it as sail-able as possible.

Almost as soon as we were home we started to try and form these ideas into a design.

The biggest change from most recent Cherubs is to move away from tubular wings to solid wings.
Under the current rules solid wings can be wings and do not have to have a continuous sheer line as per the old rules solid wing boats.

It was felt that solid wings could give a number of advantages:
•   A lot of capsizes in the new boats seem to occur at low speed whilst maneuvering. By having solid wings there are more options on where to put your weight.
•   The tubular wings often hit waves at speed this is not fast. A wave hitting the clean underside of a solid wing will not drag in the same way; it can positively add righting moment.
•   Solid wings can therefore be very slightly lower which all helps with staying upright at very low speeds.
•   When they hit the water when nearly stationary they will not sink as fast.

The hull will have small flares that run all the way to the bow and transition smoothly into the wing.

Underwater I wanted a hull shape that was not so different from the current designs but perhaps more orientated to slightly lighter winds.
The racing is closer in lighter winds, giving up time in strong wind races for time in light weather races will result in a net gain in regatta position even if it results in a degrading of the PY.
My hull design therefore has slightly more rocker than most of the new designs, but still very slightly less than Ronin. We had a number of flat out runs side by side with Ronin during the year and they did not seem to be suffering loss of top speed due to excess rocker.
The chine entry angle is much the same as the other modern designs.
The max chine beam is on the 450mm limit 85% aft. Perhaps very slightly further forward than the E6 but with no compromise to the entry angle.
Looking at pictures and from direct observations it appears to me that water only releases at the chine a small percentage of the time. Often the chine is either fully immersed or the release has happened before the chine. This is in contrast to a speed boat or a sailboard where the water truly does release at the chine.
On my hull the chines are therefore slightly higher and less defined. The hull has a tight turn of bilge below the chine with a truly flat bottom panel. The higher chine line probably means that the water line entry angle is actually finer on this design, and the mid ship water line beam may be narrower despite the max chine beam being slightly further forward.
The wetted area should be lower.
Any attached drawings are have only been developed to allow me to see how things are going to work or to allow bits to be made.
 
A key consideration was to try and find a way of building the boat whilst reaming employed and married before Alex leaves home.
This has yet to be tested.

I will post some more over the next few days and as the project progresses.

Clive

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Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #1 on: October 03, 2012, 09:07:27 AM »
Import of the sections into 3d cad package.
The lofting can not handle the wing transition.
Snout not shown.

How do I directly inset images into the text?
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Offline Stuberry

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Re: Everest 1 Cherub
« Reply #2 on: October 03, 2012, 09:22:37 AM »
Hi Clive, thanks for sharing.

What will the boat look like on the top side? Will there be a foredeck?

Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #3 on: October 03, 2012, 10:24:17 AM »
No Foredeck. I considered foredeck and under floor spinnaker but decided that they are luxuries that would not fit in the Cherub weight budget.
Wings are going to have a 49er style return to stiffen the outer edge.
There is a grey area on the rules here as it contravenes the letter of the anti multi hull rule. 4.1.6
The rule states that "Note: It is not the intention of this rule to prohibit 'tubular
wings'. These are not tubular wings. If they are deemed illegal so would all boats such as Subtle moulded with a return on their gunwale.
If this is the case I will fill the return with polystyrene, however I do not think that it is the intent of the rule.

The shrouds will be near the wing tip with horizontal compression struts going to a king post, and a mast step that is level with the wing tips. This will support the front edge of the wing.
There will be support tubes supporting the aft corners of the wings.
The forward flares should be small enough with enough compound curvature not to need support.

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Offline Ben Howett

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Re: Everest 1 Cherub
« Reply #4 on: October 03, 2012, 11:13:06 AM »
Thanks for sharing these Clive.

Im really interested to see this - The solid wings and raised/softened chines are features of a design I have had gestating for some time so its nice to see im not out on my own here. I'm looking forward to seeing the updates as things progress.

Offline phil_kirk

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Re: Everest 1 Cherub
« Reply #5 on: October 03, 2012, 11:34:12 AM »
I notice from the sketches that the wings do not extend aft of the transom.  Is this true or a simplification of the scetches done to date.  You may wish to consider kick bars along the wings where the gunnel of a racked boat would be.  These could also be used to stiffen the wing pannels.

We realised the issue of racks catching the water or deflecting spray from the boat by fitting the racks on Enumbers an inch higher than antidotes.  That appears to would most of the time.

If you are a perfectionist it can take a long time to build a boat.  But I hope that Alex will be keen to help. To speed up the build and reduce the impact on Family consider getting the shells built professionally.  You can build other components at the same time and bring the lot together.  Good luck!


Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #6 on: October 03, 2012, 11:52:53 AM »
Hi Phil,
The images in the first 2 posts do not accurately reflect the wing design. They are a simplification whilst working on the hull form.

the 3rd one is a more accurate representation of the wing detail.
The rebate in the back edge of the wing for a back foot aligns with a kick bar that runs the full length of the wing.
The kick bar can be seen on the transom view.
The wings are going to extend 400mm aft of the transom. A lot less than some wheelie bars, but by having the inboard rebate for the back foot I hope to be able to trapeze with my body angled back with a safer foot position, when sending, but have both feet on the outer edge when feeling more confident.

I have never ever been accused of being a perfectionist when it come to boat building.
I will give a bit more detail about the build process once I have done a bit of real work. It has been rather limited in the last month.

Clive
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Offline Torchy

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Re: Everest 1 Cherub
« Reply #7 on: October 03, 2012, 04:09:45 PM »
Hi Clive,

Your sketches show an even rocker approx 50% before the centreboard and 50% after.

I'm no expert but Loco's rocker appears to be more forward with flatter sections aft. (NB Big Issue) I had a good look a few months ago and came to that conclusion. The aft sections actually look to have relatively little rocker.

I think you are right about wings. We didn't get a chance to show off Loco much this year but the consensus seems to be 'Fast in light, gets left behind in medium (but not by much) and comes back in the heavy stuff'.

The 'Gets left in medium' might be cured by a better T-foil as Loco's is (I am told) of an older design.

Can't find Big Issue line drawings but I suspect Loco has more rocker than Ronin.

I think there is speed in Loco's hull and getting the right bow attitude in medium stuff could unlock it...I'll dream on anyway.
Previously 2685 'Loco Perro' and 2345 'Tachyon'

Offline ade white

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Re: Everest 1 Cherub
« Reply #8 on: October 03, 2012, 05:52:59 PM »
I agree there is more scope for this type of design to appeal to newer cherubists and crews thinking about getting into Cherubs,  (as standing on it should give alot more initial confidence than when launching yourself around a racked design for the first time!).
Good on yer Clive it looks great! I hope to see it soon. when you thinking on first time out...?
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Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #9 on: October 03, 2012, 06:17:05 PM »
To answer the above, the rocker is still low compared with almost any other class of dinghy at just 65mm.
Half of this is of constant curvature from end to end.
Half has a curvature of zero at the transom increasing linearly to the bow.
I am not looking to compromise speed against other boats. I am trying to find ways of making a full speed modern cherub slightly easier.
I hope to have it afloat for Chew.
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Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #10 on: October 03, 2012, 07:08:59 PM »
I want the build process to be as simple as possible.

The wings, decks kick bars, transom and internal structures are being built out of flat carbon foam panels by Fibre fusion.
They have a 100 ton press and make very high quality panels.
100 tons on a 8x4 sheet is equivalent to nearly 4 bar pressure. The laminate quality is well above anything that can be achieved without an autoclave.
They will then water jet cut the panels to shape.
The water jet produces a very fine clean cut with sub mm precision.
Pic shows the panel kit.

It is possible to rout out a line across one side of the panel and fold it to make gunwale returns and kick bars.
4 panels are needed.

The hull has been designed as a multi faceted planked design.
There are a total of 11 planks around the girth from the wing intersection each side.
3 planks form the turn of bilge. The change in angle from plank to plank is very small.
I have had a kit for the mould water jet cut from 6mm ply. The kit consists of 11 bulkheads and the required planks and various spacers and templates to set angles.
Pic below shows the parts drying out. If my sums are right the planks should fit to the bulkheads to form the design shape.
I will find out this weekend.
I will cover the mould with a layer of glass and self adhesive PTFE release film.
I intend to make the hull out of prepreg carbon foam sandwich.
My experience of the prepregs is that they are easier to get a high quality laminate.
You can place laminate with a lot more precision.
The resins used appear to set much harder. This will be of value on a boat that often ends up on the beach.
The laminating process requires a lot less skill and is much quicker.
The downside is that they are a bit more expensive. They need to be cooked under vacuum and any excess needs to be kept in a fridge or discarded.
The modern prepregs can be cured at 80c and will last at winter garage temperatures for several months out of the freezer.
The foam planks for the hull shell have been water jet cut today.
The first laminate and the foam will go on together.
These will be partially cured.
The corners where the planks meet will then be rounded with a long board and the second laminate applied. The whole lot will then be baked and fully cured.
The laminates join on a flange that is the same angle as the wings. The wings and deck will join onto this flange.

The internal structure will be fitted followed by the deck and wings.
I will get a pro to finish and paint it.

I will post as it progresses.

Clive

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Offline JimC

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Re: Everest 1 Cherub
« Reply #11 on: October 03, 2012, 08:49:51 PM »
Nice looking boat. Be interesting how she goes. I shall be very interested to hear how the multipanel approach works out. There are lots of potential advantages, but I've wondered if you'd lose a lot by not having all the fibres going across all the joins. Or do I misunderstand you and the shell will not have pre laminated panels?

Wings are going to have a 49er style return to stiffen the outer edge.
There is a grey area on the rules here as it contravenes the letter of the anti multi hull rule.

I can confirm it was never our intention to prohibit that sort of thing when we were writing those rules. Halo had a similar return on her (wood) gunwhales back in 1989: it was mainly intended to provide a bit more area for trapezing feet and longitudinal strength for the shroud loads on a predominantly glass boat, but it was also very handy for picking her up and for climbing onto an inverted boat!

I'd also planned vaguely similar solid wings for a width extension for Halo, and got as far as getting some panels made, although in the end (IIRC) they ended up as part of Atum Bom's interior framing. Your thinking on drag of solid wings is similar to mine - and I was also thinking about aero drag - but of course there's another school of thought that suggests you save more drag from the spray that never touches the boat than you lose from the spray that hits the beams harder. I have no idea how you'd test that.
« Last Edit: October 03, 2012, 09:02:07 PM by JimC »

Offline Clive Everest

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Re: Everest 1 Cherub
« Reply #12 on: October 03, 2012, 09:28:19 PM »
Hi Jim,
Long time since we last met.

The wings deck and internal structure will be from pre laminated panels.

The hull shell will be laminated as a single continuous moulding but the un laminated foam for the panels for the shell have been cut to the required panel shape.
The main advantage of the panelled hull is that the mould construction will hopefully be much faster.

The hull shell is a relatively small part of the structure. The shell build area is just 4.4m2 The shell uses requires 1.5 foam sheets.
The deck wings and internal structure require 3.5 sheets. Most of the build is effectively being done by fibre fusion in their 100 ton press.
The only laminating that I expect to do is the taping of the deck and wing joints.

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Offline JimC

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Re: Everest 1 Cherub
« Reply #13 on: October 03, 2012, 09:47:53 PM »
Gotcha, I understand now:-)

Press - when Halo was built Alistair and Matthew Cope showed me how to make flat panels with a press consisting of two sheets of chipboard and every sailing magazine in their house to weigh it down evenly. Somehow I doubt we made 4 bar pressure [grin].

Yeah, its about time we ran into each other again.

Offline Torchy

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Re: Everest 1 Cherub
« Reply #14 on: October 03, 2012, 10:02:34 PM »
To answer the above, the rocker is still low compared with almost any other class of dinghy at just 65mm.

Absolutely...and I'm really pleased you decided to design...and I think I was cheeky to offer you advice  :)

When I looked again I could see that the rocker was graded.
Previously 2685 'Loco Perro' and 2345 'Tachyon'