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One for a sailmaker...radial v crosscut

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Iain C View Drop Down
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Post Options Post Options   Quote Iain C Quote  Post ReplyReply Direct Link To This Post 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!!

49er GBR340 "20KSB"
Sabre 27 "Summer Girl"
Foiling Moth GBR4093 "Beermoth"
1965 Flying 15 K797 "Braveheart"
Fireball GBR14110
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Jack Sparrow View Drop Down
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Post Options Post Options   Quote Jack Sparrow Quote  Post ReplyReply Direct Link To This Post 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 View Drop Down
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Post Options Post Options   Quote Stefan Lloyd Quote  Post ReplyReply Direct Link To This Post 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 View Drop Down
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Post Options Post Options   Quote Jack Sparrow Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote Guest Quote  Post ReplyReply Direct Link To This Post 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 View Drop Down
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Post Options Post Options   Quote Stefan Lloyd Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 06 at 3:43pm

Originally posted by Jack Sparrow

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

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 View Drop Down
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Post Options Post Options   Quote Ian99 Quote  Post ReplyReply Direct Link To This Post 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 View Drop Down
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Post Options Post Options   Quote Iain C Quote  Post ReplyReply Direct Link To This Post 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.
49er GBR340 "20KSB"
Sabre 27 "Summer Girl"
Foiling Moth GBR4093 "Beermoth"
1965 Flying 15 K797 "Braveheart"
Fireball GBR14110
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Jack Sparrow View Drop Down
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Post Options Post Options   Quote Jack Sparrow Quote  Post ReplyReply Direct Link To This Post 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 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 View Drop Down
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Post Options Post Options   Quote aardvark_issues Quote  Post ReplyReply Direct Link To This Post 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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