Your point sounds valid. I guess my thinking was that the Potter just doesn't
seem to be close in comparison to something like a Herreshoff H-14. The true
displacement type design should most certainly be slower than a centerboard
design. Again, I'm not an engineer. I really don't get overly concerned about
the speed of the Potter, but I do want it to sail as efficiently as possible. I
think that is the general drift from the discussion list. It's fun to tweak the
rig and get just a little more performance. I was often surprised by the turn of
speed in my old Cape Dory Typhoon. It didn't seem to be a slow boat, yet, many
people would remark that it was because of its design.
Perry
<One reason the hull speed calculation may not hold is that the displacement
of a small boat actually decreases with speed. For the boat to initially
move ahead it must move a volume of water equal to its weight out of the
way. The water is lifted against gravity in the form of a wave, especially
when the boat speed is near the same magnitude of the wave speed (slow
moving boats dont produce large waves because the water has time to get out
of the way of the boat). The displaced water also forms a back pressure
against the hull. For a small boat this back pressure actually lifts it
slightly out of the water, decreasing its displacement but not its weight.
As the boat goes faster it displaces less and less water until in some cases
it eventually planes. The formula holds for large boats because the
displacement doesnt change much with speed.>
Jim Nolan
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Perry W. Phillips
"A better world begins with you!"
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http://www.prayercircle.org
prayercircle@prayercircle.org = For Prayer Request
1970 C Type West Wight Potter "Frodo" Un-numbered Hull
http://www.prayercircle.org/pwphil/index.html
Port Arthur, Texas (Sabine Lake/Gulf of Mexico)