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sail shapeing


wwbaginski

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Hi, after few years of sailing I identified some problems with some deformations which are to be observed constantly while underway or moored. I posted a photo showing and explaining  them, but only one reason is obvious for me and I'm working on replacing ready made plastic  battens with properly tapered wooden ones. Reasons of two else deformations stay unclear to me, so please take a look and share your comments. post-1148-0-50241200-1411447985_thumb.jpg

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Hi Wojtek

 

I'll add my 2 cents worth

The  crease at the inner end of the battens could be excessively stiff battens but could only be determined with pressure under sail- do you still have a  sharp transition when sailing?

The luff creases are common when the sprit is to leeward and there is no tension in the sail- if still present when sailing then more snotter tension and more sheet should fix it by inducing mast bend. If not then is the mast too stiff (or the sail might have too much luff round).

The creases at the foot of the mizzen I'm not sure about. ?more snotter tension needed ?more luff tension.

Cheers

Peter HK

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I don't think batten stiffness has anything to do with any of the problems.  Either the sail is poorly cut or the tensions on the sail are poorly adjusted.  A vertical wrinkle is likely luff tension too tight.  Either slack the downhaul or halyard a little.  I like to hoist the sail all the way up and control tension with the downhaul.  A horizontal wrinkle is likely outhaul tension which on a sprit rig is controlled by the snotter.  Optimal sail shape occurs when these 2 adjustments are matched to each other and the wind velocity.  Batten stiffness effects the curve, or lack of over the length of them.  This is why full batten sails have become popular. Well designed battens and careful capture tension helps create the shape of the entire sail. If the batten (not full length) is captured at the leach with considerable tension (too much for the conditions) a wrinkle may also be created. 

 

I know Graham likes sprits, and I understand why the simplicity is so desirable.  But has anyone tried using conventional booms with nothing else about the rig changed from spec?  People have been ducking under booms for many years, is it that hard to do on these designs?

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I know Graham likes sprits, and I understand why the simplicity is so desirable.  But has anyone tried using conventional booms with nothing else about the rig changed from spec?  People have been ducking under booms for many years, is it that hard to do on these designs?

Not "hard" to do, but not as simple as simply "using conventional booms" - which would not replace all of the functionality of the sprit it seems. If you want the boat to be able to sail properly that is.

 

The sprit in essence replaces the boom, the boom vang, and not unimportantly the (expensive?) multipart mainsheet tackle to a large extent.

 

That's a substantial amount of "related" gear that needs to be added in order to fully replace the lowly sprit ;)

 

Some of that can be minimized if you wish to add circular mainsheet tracks and the related control lines.

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My two cents worth --

 

Generally speaking, sails look very different when they're loaded with wind and when they're not. And (pardon me if  I'm just repeating what you already know...) performance sails are trimmed for different shapes for light air and heavy air. In light air, say 5 knots, we try for full sails with as much power as possible, and the deepest part of the camber about 45% of the distance back from luff to leech. This calls for a pretty straight mast and not much tension on the snotter and downhaul.

 

When the wind gets into the teens, we start depowering the sails. As the sail is loaded up, the shape gets deep and the camber is blown aft -- both things you don't want. So we tighten the snotter to flatten the sail and tighten the downhaul to pull the camber forward to about 40% back from the mast. A tight snotter should do two things -- push the clew aft; and bend the mast, pulling the luff forward. Also, a mast with the right flex profile will bend off at the top in heavier air, letting the upper leech twist off and spill excess wind. This helps keep the boat right side up :) You can see that it's important to match the luff curve built into the sail to the mast bend characteristics so that they work together. Graham seems to have this dialed in with his mast/sail designs.

 

To address your specific issues:

 

luff wrinkles: if the wrinkle in your foresail doesn't disappear when the sail fills with air, try easing the downhaul or applying more snotter. If you can't fix it with those adjustments, perhaps the luff curve/mast bend is out of whack.

 

batten crease: if it won't blow out when you're sailing, the battens could be too tight or too stiff. The forward ends, especially at the top, should be pretty darn flexible and not too snug in the batten pockets.

 

mizzen foot wrinkle: not too sure about this; it doesn't look critical. More downhaul or less snotter could make a difference if the overall shape of the sail stays ok, or flaking the sail for storage so that it doesn't get crunched up might help. Pictures of the rig under sail would be interesting to see; and anyway, we all like pictures of boats under sail!

 

Boy, that was pretty long winded; guess I've had enough coffee this morning...

 

good luck,

Lynn

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Many thanks, I 've had nice  and informative readings , a cup of coffee in hand either..... Few photos of BRS 17 under sails in reverse,  on coastal waters of Poland, Finland and Greece. Guess which photo comes from which country...  and by the way I'd like to introduce Flying Flaneuse, another cat ketch which consists of the yellow hull of my rowing boat, Jim Michalak designed Robote, and the sailing rig designed and made by me upon inspiration and appreciation of Graham's job. 

 

Best wishes to Carla.

 

Wojtek

 

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