Re: P15 Hull Speed
james nolan (nolan_laboratories@email.msn.com)
Mon, 21 Jun 1999 09:25:27 -0600
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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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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
-----Original Message-----
From: Perry W. Phillips <perrywphillips@prayercircle.org>
To: TillyLucy@aol.com <TillyLucy@aol.com>; remthor@earthlink.net
<remthor@earthlink.net>; wwpotter@tscnet.com <wwpotter@tscnet.com>
Date: Sunday, June 20, 1999 7:38 AM
Subject: Re: P15 Hull Speed
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> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
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>Regarding hull speed, Ferenc Mate reports in his book "Best Boats" that the
>formula for determining hull speed breaks down on boats with a waterline
length
>less than 20 ft. His indication was that well built displacement hulls
(such as
>a Flicka) consistently experienced better speeds than would be allowed by
the
>mathematical formula. He also stated that no one really knew why the
formula
>was supposed to work in the first place. Apparently, it was someones best
guess
>explanation. He did attest to its accuracy on larger boats, however.
Since I'm
>a preacher and not a mathematician, I'll take his word for it.
>
>-------------------------------------------------
>Perry W. Phillips
>"A better world begins with you!"
>-------------------------------------------------
>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)
>