Doug,
From what I can see on Brett's NZ proa, he's got a standard single-skin junk rig that doesn't create an airfoil shape. If that's true, the sail would indeed be pushing against the mast on one shunt and pulling away on another.
The swing-wing is a different design, though, with double-sided wishbones that create a sail with two skins.
The way the wishbones work is that the leeward edge of the sail has a nice smooth curve to it, while the windward side gets the kink. This is less than ideal, but also still a better airfoil than a single skin sail. For each shunt, the leeward surface is smooth.
To get a better idea of how it works, check out these photos:
Nice leeward surface for generating lift:
http://api.ning.com/files/OX6wi*XepeSFiOcN2A1LCruxG28UbW2T02hM1KC3mXMkg5J5D*9b2qh2350oH2Rv9oBLKC3AuWV9WVK3HiLPURXItsWuRpJb/178f2009042200PHAwithitsnewdoublewisbonesintandem.JPG Corresponding kinked windward surface:
http://api.ning.com/files/8ZicrvcPCMAFxbwHBScmeROW*xJLvh1BnaXKVECpl9rETD3muuQn3pqV0nlR3LNyk6JoZyiD-TBUivh0Bmsl8yxjrNX*bsNh/178gUKJRA0002.JPG Interior (to see how things might push against the mast):
http://api.ning.com/files/-1yR27opppagPAzdnm*JUW1PwlPrg*WP4CHraDW*Yptmb-pI6CheiXxsLX2itDcZSVU3AbJyOktv7NdXUO*0KzkHniwieOY0/176b200806010037.JPG - Mike
Doug Haines wrote:
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For the unbelievers, I might say that the thing looks like a pile of crap - but somehow seems to go alright (James Brett's NZ proa on youtube) and get's favourable comments.
How can the sail have good curving when it has to go on one side of the mast - which looks ok one one tack/shunt, but then it pushes into the mast and must make a huge kink in sail shape when on your other tack(shunt)?
The battens would be pushed up hard against the mast (like sail against spreaders on normal boat). The tack with the wind cxominjg from ......need drawing.
Wondering if we could infiltrate Sailing Anarchy, just so as to use more photo uploading things
DOug |