mainsail wrinkles

Submitted by frank barbehenn on Thu, 06/07/2007 - 16:43
I do not understand the advice about using wrinkles as a gauge for the mainsail. The reason: planes are not made with wrinkled wings. What sense does it make to have wrinkles in the sail, except that for some reason the sail is too big for light to medium air in particular, then we tighten everything up as much as possible for very heavy air. Can someone explain to me, "why wrinkles??" besides the fact that that is simply the way it's done. Frank
‹ What happend to the NAC's topic? gybing the spinaker on a broad reach ›

Comments

My understanding of this is the luff wrinkles themselves are not

Submitted by Dave812 on Thu, 06/07/2007 - 21:08.
My understanding of this is the luff wrinkles themselves are not fast but are an indicator you can use to help determine the proper draft in your sails. Lets say you hoist your sails at the dock and after you sail out to the racing area and go upwind a bit you notice there are little or no luff wrinkles in the main. This would be an indication that your halyard and/or cunningham tension is too tight and should be eased until some wrinkles appear. It is probably easier for most of us to use the wrinkles as a guide rather than being able to accurately look at our sail and determine the correct draft for the wind and wave conditions. Most of the pros can look at the draft itself and see whether it is correct or not. Hope this helps.

yes, this helps some, but why is the sail designed in such a way

Submitted by frank barbehenn on Thu, 06/07/2007 - 23:13.
yes, this helps some, but why is the sail designed in such a way as to have wrinkles? Why not design it so that the draft is in the correct position without wrinkles?

The sails are designed for a wide range of wind conditions, whic

Submitted by Dave812 on Sun, 06/10/2007 - 09:09.
The sails are designed for a wide range of wind conditions, which require different adjustments to get the correct shape. Also, as the sail ages, it stretches and the draft moves aft so more halyard and cunningham tension can help make up for the aging of the sail.

Frank, Per your note: Dave's explanation is consistent with ev

Submitted by Gallus 102 on Wed, 06/13/2007 - 09:45.
Frank, Per your note: Dave's explanation is consistent with everything I've read on the subject. As to the wrinkles themselves, they don't seem to matter very much in terms of aero-dynamic efficiency. My understanding is that it is due to 1) the sails (foils) operate at low Reynolds numbers where the effects are not as critical (though they exist) and 2) that the main-jib interaction is best thought of as a multi-element airfoil and the leading edge is the jib, not the forward part of the main. The wrinkles are in a part of the multi-element foil where they don't matter very much. For a much more thorough explanation of the sail aero-dynamics, see the series of articles from Arvel Gentry: http://www.arvelgentry.com/

Regarding sail wrinkles I would like to parody the Miss Clairol

Submitted by karafiath on Tue, 06/19/2007 - 13:01.
Regarding sail wrinkles I would like to parody the Miss Clairol phrase, "Only your sailmaker knows for sure ". I suspect that the use of wrinkles allows the sail to be assembled with a minimum of broadseaming. Broadseaming is the slight tapering of each sail panel so that the standard width sail material is cut so that it's width is no longer uniform. Alternatively, the seam width can be varied on a unifom sail panel to achieve the same effect. In the middle of the sail there is somewahat greater effective pannel width so there ends up to me more cloth and shape to the sail when hoisted. Without broadseaming, the sail would like perfectly flat on the floor. It is far easier to assemble a sail without broad seaming using only luff round and foot round or a foot shelf than to slightly adjust the width of each piece of sail material or the width of the seam. So the question is how do you put shape into the sail? To broadseam is more expensive. Not to broadseam and achieve the shape by luff round and foot round and relaxing the tension along the mast and foot is less expensive. Or some intermediate combination may be used. If you want to find out, accurately measure the width of each sail pannel at three points, along the leach, in the middle and at the luff on a reasonably new sail. Even if broadseaming and luff and foot round is used to achieve the sail shape, the shape will probably be optimum for just a narrow range of wind speeds and at significantly lower wind speeds you will want a fuller sail and relax the foot and luff tension and get wrinkles anyway. Also keep in mind that Flying Scot sails in my opinion are very competatively priced on a cost per sq ft basis for most makers of the sail except perhaps for the most expensive sailmaker. Some quotes for new sails on less popular one design classes are very close to the Flying Scot sail price even though the sail area is far less.