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SoggyBadger View Drop Down
Really should get out more
Really should get out more


Joined: 26 Oct 10
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Post Options Post Options   Quote SoggyBadger Quote  Post ReplyReply Direct Link To This Post Posted: 12 May 19 at 7:04pm
Originally posted by Sam.Spoons


Surely the flow across the sail is mostly horizontal (that's what my teltails tell me) so a vertical creases is across the flow?


And your tell-tails are telling the truth. I'm rather confused about where you think this vertical crease comes from though? I've not seen one of those which was causes by anything other than too much Cunningham or luff tension, neither of which is related to the sail's panel layout.
Best wishes from deep in the woods

SB

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Sam.Spoons View Drop Down
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 12 May 19 at 10:23pm
Sorry, clearly cross purposes, I was referring to the vertical wrinkles you mentioned. I agree that wrinkles (as opposed to 'creases' though that was the term Sean Cox used) do fall within the boundary layer and don't affect performance.

I believe creases/wrinkles are common when a sail is tensioned beyond (or below) its design limits and the limits of adjustment are exceeded. Sailcloth with more stretch will accommodate a wider range of adjustment/shape but will hold it's shape less well under load and will have sub standard high wind performance. A low stretch cloth will make a sail which keeps it's shape better under load but will have less range of adjustment and be 'stiffer' and harder to read in light winds. Under load the aim is to allow gust response but keep the CoE reasonably constant so the sail spills in the gusts without unduly moving the CoE. Floppy head designs in windsurfing which set on downhaul alone are a perfect example but they tend to be slow in lighter winds. Dinghies have and significantly more sophisticated rig controls so can cope with a wider range of wind speeds with a single sail so the dinghy equivalent is a bendy mast and lots of cunningham.
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