Re: Genoa tracks

Kent Crispin (kent@songbird.com)
Thu, 4 Mar 1999 15:54:02 -0800


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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On Thu, Mar 04, 1999 at 02:29:09PM -0800, DAVID_KAUTZ@HP-Sunnyvale-om5.om.hp.com wrote:
> Judy,
>
> I'm still having trouble with your observations - the physics of the
> situation don't indicate the results you're seeing.
>
> As you point higher the apparent wind increases in proportion to the Cosine
> of your decreasing pointing angle. The portion of the lift vector that
> provides forward thrust varies as the Tangent of the angle. This means that
> if you sailing with an apparent wind 35 degrees off the bow and you now
> point 10 degrees higher, your new sheeting angle becoming 25 degrees, the
> apparent wind will increase by 9% (increasing lift by slightly less than
> that, thanks to the proportional increase is drag) but your forward thrust
> from that lift will DROP by 32%.

However, given the winds on the Bay, it may still be *substantially*
more than is necessary to drive the boat at hull speed...obviously,
light wind sailing could give you very different results.

Hull speed and other drag elements are important factors -- as I
mentioned earlier, ice boats can point incredibly high, because they
get going so fast that the apparent wind is radically shifted from
the true wind.

[...]
>
> Kent, maybe you can check my Math - it's been a long time since I took
> Trig.

I really have to think about it -- when you bring lift into it
things get *much* more complicated.

-- 
Kent Crispin                               "Do good, and you'll be
kent@songbird.com                           lonesome." -- Mark Twain