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By the way, contrary to an earlier quote, a floppy leach is probably not like a winglet or endplate. A floppy leach seems to basically be what wing designers call "washout", which is the opposite of a winglet. Washout reduces lift at the tip, winglets increase it.
It would be interesting to find out more about how washout and floppy leaches work in sails.
Gotta say when I posted the quote I wasn't super impressed by the explanation as the top of a floppy sail probably doesn't behave like the end of a plane wing but beyond that its probably way to complex for me beyond knowing that the sails I used back in the eighties were all pretty ordinary. In fact I think they got a lot worse (heavier and more expensive) before they finally improved.
I agree with him that twist is not needed. There must be sails around that are contrary to what we've been doing for the last few decades, and I bet they work just fine. Wing11, do you have any examples of such a thing?
Even if you dont trim sail with twist=less downhaul , sail allways have slighlty twist shape when sailing,because pressure make this shape.
Sail is not rigid,upper part allways slighty twist to leeward.
Great pic showing huge twist and he's the fastest in the buisiness.
Looks like the bottom is working like a plane wing and the top more like the wind hitting a angled sheet ( pushing forward ) and the middle half way between.???
Maybee the top is holding the bottom steady. I reckon there's heaps of different dynamics working together.
If there just now grasping how a normal plane wing actually works , ( and there is still debate ) , this twisting thing ain't going to be that simple to explain.
Saying that , the speed breaking boats use a solid narrow straight simple wing.
If the fastest windsurf sails have such a huge luff pocket and they are halfway a wing anyway , why not go all the way.
Twisty topped wing sail ???
We know we want to like them.
On all other sailing vessels there is a tripod affect that can take up variances .
On a windsurfer it's a 100% equal , opposite balance. Mabee we need twisty , flexy , to match what our body does.
Windsurf Sails do more and more mimic bird wings , which are the absolute best at what they do. And they have millions of years of no compromise evolution on there sides.
Sail did not has floppy leech/head,but sail was more narrow/pointed on top , small area in top make less overturnnig moment.
Also narrow head/small area =less induce drag.
Today race sail has bigger head area,but floppy.
good old times!
and that is seabreezer Roo on the left holding the board, and Pascal Maka in the middle
The twist was a byproduct of trying to reduce pitching moment in the sail. On a windy day when the trailing edge of the tip was pushed up with a stick the pitching reduced as the center of pressure moved down in the sail, the numbers being spat out by the computer showed it. Gaastra were the first to take advantage of it, they also owned Rushwind at the time. Here's a double surface wingsail we were also testing at the time.
^^^^ Good to see when u fell off that thing on a salt late, you only ended up with such a small graze on ya knee 
