William R. Watt wrote:

no, there's got to be a formula relating wind speed, sail area, and
horsepower.

THe formula for wind pressure perpindicular to a flat surface is
P = 1/2p × V² the p is the specific mass of the air which varies due to
temperature and humidity but somewhere around .0022 but that is just the
beginning. There are other rather complicated formulas for calculating
lift and drag that are way over my head.


In Dave Gerr's book there is a sort of rule of thumb wind speed/HP
table: At 9-10 Kn a sail can produce .015 HP/sq. ft. At 13-15 Kn it is
..020 HP and at 19-21 Kn .040 HP.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Glenn Ashmore ) writes:

THe formula for wind pressure perpindicular to a flat surface is
P = 1/2p × V² the p is the specific mass of the air which varies due to
temperature and humidity but somewhere around .0022 but that is just the
beginning. There are other rather complicated formulas for calculating
lift and drag that are way over my head.

I'm sure its all been worked out by aeronautical engineers, but for higher
relative wind speeds.

In Dave Gerr's book there is a sort of rule of thumb wind speed/HP
table: At 9-10 Kn a sail can produce .015 HP/sq. ft. At 13-15 Kn it is
.020 HP and at 19-21 Kn .040 HP.

thanks. I have that. Its the best info for sails I have been able to find
to work with so far, but a bit course.



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