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Old 28th April 2009, 09:46 PM   #14
C two four nine
Posts: n/a

Good poin!

By the way, even very open-minded boat classes with no rig limits have found that wing masts, double luff sails etc are often less efficient than just making a taller, lighter, simpler rig that cuts down on induced drag by its longer span.

There's pics of double-surface windsurfer sails in use (slowly) at speed trials as early as about '82. They still seem to have an attraction because people believe that gliders are the best model for sails, and while I'm no aero expert in any way it's interesting to see that guys like Drela seems to believe that "normal" sails are better in many ways, particularly (as you pointed out) their adjustability; I can recall a post to a glider forum where he seemed very impressed by the way teh America's Cup rigs worked.

Tom Speer (a Boeing aerodynamicist who posts on Boat Design Forum) has noted when writing about solid wing sails that "the notion that because aircraft wings are very efficient and have thick sections, while sails have thin sections and generally lower lift/drag ratios, and therefore a thick sectioned sail will aerodynamically superior to a sail rig with a thin section simply because it is thick, is a mistaken idea. Airplanes have thick sections because they are structurally stronger and because they have to operate efficiently at low lift coefficients in cruise. This is generally not the case for most sailing craft, except for very high-speed craft like landyachts and iceboats."
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