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One for a sailmaker...radial v crosscut |
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Iain C
Really should get out more Joined: 16 Mar 04 Location: United Kingdom Online Status: Offline Posts: 1113 |
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Topic: One for a sailmaker...radial v crosscut Posted: 13 Sep 06 at 1:15pm |
I'm about to get a new Fireball mainsail in kevlar. When these came out they tended to be crosscut, however now there are more options available. You can still buy a fully crosscut sail, however you can now also get a mainly crosscut sail with the area under the bottom batten radial from the clew, and also a fully radial design (eg North Sails). Over time the Fireball kevlar main seems to develop a problem with a crease developing from the clew up through the inboard ends of the batten pockets and I understand that the semi radial or fully radial design can help stop this. Any sailmakers care to share some pearls of wisdom on the merits of the designs? Thanks!! |
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RS700 GBR922 "Wirespeed"
Fireball GBR14474 "Eleven Parsecs" Enterprise GBR21970 Bavaria 32 GBR4755L "Adastra" |
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Jack Sparrow
Really should get out more Joined: 08 Feb 05 Location: United Kingdom Online Status: Offline Posts: 2965 |
Post Options Quote Reply Posted: 13 Sep 06 at 1:41pm |
OK not a sail maker - EX kite maker instead.
Think about the loading on the warp and weft of the material and surely Iain would understand why it Radial is better, you rebuild half your boat after all! But fully Radial is more costly. more seems - more cuts - more planning - more difficult to design e.t.c but will give you a more consistent shape over time. Cross cut is cheaper- but the loads, however you orientate the fabric will at some point go diagonally across the warp and weft and effect the shape and over stress the material... but - less seems - less cuts - economical e.t.c A combination of both can be a good compromise. I'm fully expecting to be shot down in flames by qualified sail-maker on this but that's how I used to use my fabrics. |
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Stefan Lloyd
Really should get out more Joined: 03 Aug 04 Online Status: Offline Posts: 1599 |
Post Options Quote Reply Posted: 13 Sep 06 at 2:22pm |
Kite material stretches. Kevlar doesn't stretch - at least not much on a sail the size of a Fireball. I'd be surprised if cross-cut versus radial made much difference. But I'm not a sailmaker either.
Edited by Stefan Lloyd |
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Jack Sparrow
Really should get out more Joined: 08 Feb 05 Location: United Kingdom Online Status: Offline Posts: 2965 |
Post Options Quote Reply Posted: 13 Sep 06 at 2:29pm |
go here if you want it in black and white from a sail making source and
not a kite making one: http:/ /www.kempsails.com/da/11252 |
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Guest
Newbie Joined: 21 May 04 Location: United Kingdom Online Status: Offline Posts: 0 |
Post Options Quote Reply Posted: 13 Sep 06 at 2:31pm |
I am with Stefan - on a sail as small as a Fireball with cloth that stable I doubt it makes any difference. Choose what all the top guys use ... |
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Stefan Lloyd
Really should get out more Joined: 03 Aug 04 Online Status: Offline Posts: 1599 |
Post Options Quote Reply Posted: 13 Sep 06 at 3:43pm |
Which is all true but there are scale effects. Radial construction originated for yacht spinnakers, where 40-50 foot yachts use the same cloth as dinghies. Fashion, as much as anything else, drove the construction down to dinghies, where the forces involved are tiny by comparison. Dinghies use the same cloth not because of the stretch forces involved but because anything lighter gets punctured too easily. Same for kevlar mains. A 35 footer might use the same cloth as a dinghy, because something the weight of a crisp packet might handle the stretch forces alright on a dinghy but it isn't robust enough. Radial construction will make a difference to a 35 footer, but on a dinghy, I'm not too convinced. Edited by Stefan Lloyd |
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Ian99
Posting king Joined: 07 Apr 05 Online Status: Offline Posts: 138 |
Post Options Quote Reply Posted: 13 Sep 06 at 3:57pm |
It probably depends on the cloth - you're best off trusting the sailmaker to to have made these kind of decisions to get the fastest sail. If you suspect its only cross cut to save money, ask why it's cross cut - with most sailmakers I suspect the answer would probably take at least half an hour - I doubt few if any would just say "because it is" On the subject of the batten pocket crease, given that it never occurred with dacron sails which are like elastic compared to Kevlar cloth, there may be other powers at work. I've heard rumours its something to do with the mast bending off sideways too much below the spreaders.....
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Iain C
Really should get out more Joined: 16 Mar 04 Location: United Kingdom Online Status: Offline Posts: 1113 |
Post Options Quote Reply Posted: 13 Sep 06 at 4:39pm |
The crease issue was apparently casued by the laminate sails shrinking, not stretching. Basically the leech tries to go towards the mast, and the battens make the crease.
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RS700 GBR922 "Wirespeed"
Fireball GBR14474 "Eleven Parsecs" Enterprise GBR21970 Bavaria 32 GBR4755L "Adastra" |
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Jack Sparrow
Really should get out more Joined: 08 Feb 05 Location: United Kingdom Online Status: Offline Posts: 2965 |
Post Options Quote Reply Posted: 13 Sep 06 at 5:12pm |
Looking at it from another direction:
taken from Ullman sails web-site ( fiberpath is a load path sail technology ): ============================================= " How FiberPath Works Why have we developed FiberPath sails? The answer is that because the fibers in a FiberPath sail are aligned with the primary loads in the sail, and a FiberPath sail can be built with multiple fiber patterns to address secondary loads, a FiberPath sail has a wider range and is stronger for its weight than a tri-radial sail. The trouble with tri-radial sails is they only cover primary loads. Because the fibers in FiberPath sails run on top of each other in different directions, specific loads in each area of the sail can be handled. FiberPath Performance Life and Longevity A FiberPath sail will hold its performance shape 1 ½ to 2 times longer than a tri-radial sail, because in a tri-radial sail it is the secondary loads and Mylar shrinkage that ruin the shape." ============================================ So the shrinkage is from the mylar. this shrinkage is probably more obvious in the cross cut sail because of the bigger panels, the overall kevlar warp - weft direction and less seems - against - more seems, smaller panels, 3D panel shape and kevlar orientation on a radial sail. by the way Steffan kites aren't just made from Ripstop. |
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aardvark_issues
Really should get out more Joined: 24 Jul 05 Location: Weston-Super-Mare Online Status: Offline Posts: 505 |
Post Options Quote Reply Posted: 13 Sep 06 at 5:36pm |
I'm with Jack on this one. Most of the lighter Kevlar materials I have
seen/used on dinghies recently use a diamond style weave.
It must follow that the cloth is stiffer on the long dimension of the diamond than across it as the load will be pulled at less than 45 degrees, as opposed to more. Even a carbon pattern like this will have some spring to it and is then relying on the mylar to carry the load... If a Fibre is good in tension, use it in tension... Edited by aardvark_issues |
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