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mrgybe



Joined: 01 Jul 2008
Posts: 2611

PostPosted: Tue Nov 27, 2012 11:38 am    Post subject: Reply with quote

Anyone know if the the "weight" cited for the sailors is their own body weight......or does it include a weight vest? If not Dunkerbeck is 225. Bigger than I thought.
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boardsurfr



Joined: 23 Aug 2001
Posts: 543

PostPosted: Tue Nov 27, 2012 1:13 pm    Post subject: Reply with quote

lasrer wrote:
I suspect less twist because at that speed in 30kts of wind, there is less vertical gradient of the apparent wind.

I always wondered about why sail twist works, especially the huge twist you see in race sails. The wind velocity gradient is not that big; slalom sailors are often going 1.5 x wind speed in chop, and > 2 times in lighter winds on flat water. Head wind dominates, and it does not have a velocity gradient.

One of the possible reasons why large head twists in race sails work is that they broaden the response curve of the sail. Gusts will change the apparent wind direction even if the true wind direction does not change. With a narrow response curve (think about old sails without twist), this would lead to big changes in forces and force direction. A broader curve due to twist would steady things out a lot. I'd love to see comparison of force curves for sails with different amount of twist.
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Iceratz



Joined: 16 Feb 2009
Posts: 329

PostPosted: Tue Nov 27, 2012 4:27 pm    Post subject: Reply with quote

Twist in windsurfing sails has more to do with ease of control than aerodynamics of wind gradient and apparent wind forces.

Tighter leeches are faster, but not as controlable.
On Ice, a tight leech is very easy to hold, where on water it becomes too twitchy.
Whereas, a floppy leech on Ice is hampered severely for speed due to drag.

...and Sailrocket2 is in a different league defining what is possible....
BTW, they can manually control the shape of the rigid foil... on the fly.
They also control the angles of hydrofoils as well.
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Iceratz



Joined: 16 Feb 2009
Posts: 329

PostPosted: Wed Nov 28, 2012 1:39 pm    Post subject: Reply with quote

Here is Sailrockets latest video of speed record!

http://www.youtube.com/watch?v=pipGWQmerEQ
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