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  #11  
Old 04-01-2004
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what''''s up with sail twist?

I diagree with the point about needing more twist in waves. More twist in wave and wind means more heeling, and less drive and speed. Trimming the whole sail for an average setting setting (even if that means less twist) means that you have the whole sail working optimally more of the time even if the sail suffers small stalling and low angle of attacks at the end of each swing.

Jeff
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Old 04-01-2004
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what''''s up with sail twist?

Jeff -- I''m interested in your comment about not wanting more twist in waves, since it runs directly counter to the conventional wisdom (e.g., Dobbs Davis''s article right here on Sailnet, or Stewart Walker, or Peter Isler / Vince Brun to pick on a few.)

But oftentimes people who defy the conventional wisdom, especially people like you who are clearly coming from a position of solid theoretical and practical knowledge, are onto something interesting. Care to elaborate?
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Old 04-02-2004
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what''''s up with sail twist?

Well, even people like myself can learn something from the likes of Isler, Walker and Brun. I have generally followed the approach of setting the sail for optimum drive at an average position and carried minimal twist (but quite powered up) in a chop. It has generally been quite successful and came to the conclusion that it was faster in one-design keel boat racing where I could check it against competition and the sails, but given the sources, I guess I may need to experiement with carrying more twist in a chop.

The only other thing is that most of my current sailing and racing is in petty large boats (J-22''s, Cat 27''s, J-105''s, Farr 11.6 and a 40.7) and perhaps twist works better in smaller boats. I''ll just have to give it a try next time that I am in a chop and need to open up on a competitor. Thanks for the input.

Jeff
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what''''s up with sail twist?

I dunno -- I''m not much of a sailing expert -- I''ve spent more time in the library than on the racecourse... But I do know something about the development of technical ideas in science and engineering, and I know that often times ideas are really faddish. The "conventional wisdom" becomes accepted simply by repetition... The experts all start quoting each other, and pretty soon everyone starts accepting something (like "more twist in waves") as gospel truth without actually going out and doing the hard work of experimenting.

That''s why I got interested in your contrrarian position, especially given your willingness to experiment for yourself.
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Old 04-02-2004
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what''''s up with sail twist?

Your statement of ''conventional wisdom....." is profound!
Hint: Compare the ''twist'' on such things as turbine blades and propellers to the ''twist'' on sails. You''ll find that for regimes of greater ''tip speed'' you''ll find correspondingly less ''twist''; the ''conventional wisdom'' here avoiding that the greater the velocity over a foil/wing requires LESS angle of attack and less camber, etc. Just an aerodynamic fact. You dont ever want to disagree with the conventional ''experts''. But then again the same arguements will apply to ''slot effect'' vs. ''conventional wisdom'' ;-)
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Old 09-08-2004
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what''''s up with sail twist?

hey, this is a lot of fascinating information about sail twist which i look forward to studying the next time i''m at work.
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