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One for a sailmaker...radial v crosscut

Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=2197
Printed Date: 23 Aug 19 at 8:52pm
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Topic: One for a sailmaker...radial v crosscut
Posted By: Iain C
Subject: One for a sailmaker...radial v crosscut
Date 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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49er GBR340 "20KSB"
Sabre 27 "Summer Girl"
Foiling Moth GBR4093 "Beermoth"
1965 Flying 15 K797 "Braveheart"
Fireball GBR14110



Replies:
Posted By: Jack Sparrow
Date 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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Posted By: Stefan Lloyd
Date 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.


Posted By: Jack Sparrow
Date 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 - http:/
/www.kempsails.com/da/11252

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Posted By: Guest
Date 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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Posted By: Stefan Lloyd
Date 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 - 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.



Posted By: Ian99
Date 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.....

 



Posted By: Iain C
Date 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


Posted By: Jack Sparrow
Date 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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Posted By: aardvark_issues
Date 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...


Posted By: JimC
Date Posted: 13 Sep 06 at 7:00pm
Originally posted by Ian99

On the subject of the batten pocket crease, given that it never occurred with dacron sails which are like elastic compared to Kevlar cloth



It didn't? Are you sure? I've seen planty of tired old dacron sails with batten poke, although I can't especially recall whether any of them were Fireball ones.


Posted By: a_stevo
Date Posted: 13 Sep 06 at 10:48pm

i agree with stefan and rick on this.

in high load, big sails the of axis loads can be a major issue. in dinghys it is marginal.

best bet in my opinion is to split the difference.

-use a cloth with a diagonal warp as well as the major fibres, for stability.

-then align the back half of the sail with the leach and the front half with the luff.



Posted By: Stefan Lloyd
Date Posted: 14 Sep 06 at 8:12am

Originally posted by Jack Sparrow

by the way Steffan kites aren't just made from Ripstop.

What are they made of? I admit it is a few decades since I bought a kite. (We are talking actual kites here, not spinnakers.)



Posted By: Paramedic
Date Posted: 14 Sep 06 at 8:31am

The main issue with most kevlar cloths is that the mylar laminate is too thin, it has almost no resistance to creasing and breaks down very quickly.

Even if the sails are handled with kid gloves their lastability is unacceptable for an item that costs 600+.



Posted By: Jack Sparrow
Date Posted: 14 Sep 06 at 9:46am
Originally posted by Stefan Lloyd

Originally posted by Jack Sparrow

by the way Steffan kites
aren't just made from Ripstop.


What are they made of? I admit it is a few decades since I bought a kite.
(We are talking actual kites here, not spinnakers.)



Ripstop - many types ( Carrington K42 e.t.c )
Dacron's
Mylar laminates
Nylon mesh venting
Dyneema / Spectra (anti leech motivators e.t.c)
A myriad of carbon and fibreglass tube types

Loads of stuff in fact.

What's more when you have put all that together it needs to fly.
but not only fly, fly in a particular fashion to your design brief.
especially if you are developing stunt kites -
( competition, trick of team )

why not go here : http://www.kitebuilder.com/plans/sport.htm
and have a go yourself. It's a lot of fun and you can learn a lot.



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Posted By: Isis
Date Posted: 14 Sep 06 at 11:24am
Originally posted by Paramedic

The main issue with most kevlar cloths is that the mylar laminate is too thin, it has almost no resistance to creasing and breaks down very quickly.

Even if the sails are handled with kid gloves their lastability is unacceptable for an item that costs 600+.



Im not sure about unaccetable.. How long does a far more expensive F1 engne last? a race? but from that you get far better performace than one designed to cope with several seasons.
If you choose the grater performace of a laminate sail you accept it will tend to have a shorter lifelifespan... if you dont like it stick with dacron.


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Posted By: Paramedic
Date Posted: 14 Sep 06 at 12:40pm

Originally posted by Isis


Im not sure about unaccetable.. How long does a far more expensive F1 engne last? a race? but from that you get far better performace than one designed to cope with several seasons.
If you choose the grater performace of a laminate sail you accept it will tend to have a shorter lifelifespan... if you dont like it stick with dacron.

The far more expensive formula 1 engine is being used by professional drivers and is not paid for out of the driver's pocket.

I'm not even sure that Kevlar laminate performs any better than the older - albeit slightly heavier - polyester laminate we were using 5 years ago, but the big differance is you could get a full competetive season out of a polyester scrim sail. Some people are changing Kevlar sails after about 3 months use. (To be fair the very top sailors probably did with polyester then too).

There are many laminate alternatives to kevlar, but for some reason people seem unwilling to try them. It strikes me that as far as practicality goes the kevlar cloths on offer are unsuitable for dinghies becasue it is impossible to prevent the creasing that casues so much harm. The polyester scrim cloths seemed to have more mylar and resisted the cracking much better.

Interestingly back on topic, many classes that have tried radial cut mains have now gone back to crosscuts or hybrids.

Norths make a very odd looking radial jib for the Enterprise.



Posted By: JimC
Date Posted: 14 Sep 06 at 2:05pm
Originally posted by Paramedic

The far more expensive formula 1 engine is being used by professional drivers and is not paid for out of the driver's pocket.


Sure, but when I was periphally involved with bike racing a set of pistons were worth 250 miles and a crankshaft rebuild every 2000... That is not a lot of races and that was coming out of the riders pocket.

I've never use kevlar sails, but the carbon/mylar sails on my last Cherub seemed to be lasting fine no probs when I sold them after two and a half seasons. However they were full battened sails which don't suffer from the batten poke problem anyway.


Posted By: Ian99
Date Posted: 14 Sep 06 at 7:22pm

Dacron racing sails lasting longer than kevlar is a myth. True, the absolute "life" of the sail, (the time until it falls apart) is much longer for a dacron sail, but after a season's use a dacron sail is well past its best. You can still make it look nice for photographs by doing tricks like pulling the cunningham on, but the performance is rubbish compared to a season old kevlar sail.

The Kevlar main on my Fireball (incidentally with a radial bottom section and cross cut upper) has been used for 2 Europeans, 2 Nationals and a Worlds, loads of windy opens and quite a bit of club racing, and hasn't really changed in shape very much even though the cloth hardly looks new any more! I doubt you'd get that much out of a dacron sail.

You do have to look after them, and not do stupid things like leaving them flogging on the jetty or routinely drying them out in direct sunlight, but I'd never go and buy dacron sails if there's an option to get something better.




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