RE: what is your bananafish?

There's two ways of moving on the surface of water. The first is
displacement and is the most stable the second is planing and the least
stable. A displacemet hull pushes or plows a wave and the ship rides in the
valley of this wave that is why its speed is limited since it can only push
so big a wave. Now a hydo-planing craft rides up out of the water, as the
water line approachs the screw the craft becomes increasingly uncontrollable
and susceptible to distablizing forces, watch a speed boat race. Now,
engineers have come up with compromises. For the planing craft they
developed hydro-foils which allow it to climb up on legs with wings for
feet, a mercury image. Fo displacement craft there are several ways to to
'ride' out of the wave trough. In the age of sail the Americans piled on
incredible amounts of sail and shifted the center of effort to the stern
which lifted the bows to help it 'climb' the wave. Now the bulb at the bow
I believe (I am not totally sure) has more to do with 'cutting' the water to
allow for a bigger wave thus higher speed not directly limited to hull
length. It's actual effectsare that it helps when getting up to speed and
alleviates power to displacement problems. You get more bang for your
engine buck. Now, bulbs on the keels of sailboats are to increase final
stability to allow for more sail area.

Daniel
more than you ever needed to know.

-----Original Message-----
From: Scottie Bowman [mailto:rbowman@indigo.ie]
Sent: Wednesday, December 18, 2002 11:32 AM
To: bananafish@roughdraft.org
Subject: Re: what is your bananafish?

    '...1.333 times the square root of its water line length ...' etc.

    Which is, I understand, one of the reasons for the 'bulb'
    extending beneath the prow of so many modern ships.
    (Something about drag reduced by an exact number of
    waves - ? 3 ? - at the waterline.)
    Yet I don't THINK destroyers or their like carry such
    probosces. Wrong?

    Scottie B.

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Received on Wed Dec 18 15:26:15 2002