Subject: Re: [baidarka] Re: Sail Plans
From: Tom Yost (tom_yost@msn.com)
Date: Mon Sep 08 2003 - 10:40:39 EDT
Here is Mladen's response to questions raised regarding the Downwind
capabilities of the wingsail. I don't believe his post made it to the forum.
>>>Mladens Response
Hi everybody,
I think I've given a theoretical basis for "Bernoulli" (as I call it)
downwind sailing. Interestingly, it works in practice. Of course, NOT dead
downwind, but let's say up to some 160 degrees to the wind (or off the wind?).
With your daggerboard or leeboards retrieved, you can easily end up at '179
dgs'. Most racing boats don't sail dead downwind, particularly with
asymmetrical spinnakers. Sailing strictly downwind is associated with
pitching, rolling and even broaching and essentially is not faster than
sailing under a small angle. Conventional stayed rigs don't allow this type of
sailing, since their booms have limited tacking/gybing range (from shroud to
shroud). Generally, the potential of aerodynamic force for downwind sailing
(vs. force of resistance of a lateral plane) is highly underestimated. Should
I remind you that if an America's Cup boat speed on its upwind leg is, say, 11
knots, its downwind speed with many times larger sail area is not more than 12
knots? Isn't this paradoxical? Hopefully, somebody from scientific and design
circles will take this seriously - some day. You can always make sailing more
complicated making it simple is far more difficult. Is the current "push
button sailing" really that?
Yes, a wingsail downwind will produce some heeling, but far less than on
upwind beat (to which we all got used to, btw) and far from capsizing. I've
sailed a lot - and never capsized.
Cheers,
Mladen
www.wingsails.com
(P.S. Wingsails are not as much about their aspect ratios as they are about
thickening of their profiles)
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