that pesky floatation

Bernard Johnson (
Thu, 06 May 1999 18:53:08 -0700

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West Wight Potter Website at URL
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It seems I struck a chord with my floatation comment. Let me explain my
line of reasoning. I propose to put the floatation in the bottom mainly,
because the way I see it, if the volume of water displaced by the boat
is equaled by the same amount of floatation material, OCCUPYING THE
SPACE THAT THE WATER IS DISPLACED FROM, that is, level with (preferably
a little higher) the water line inside the hull, then any water entering
the boat would be held ABOVE the outside water level, thus possessing
potential energy and having a desire to seek it's own level. If suitable
drains were provided the hull would become self bailing removing
concerns about the boat becoming swamped, and of course the top of the
trunk would be as far above water level as it normally is. This self
bailing can easily be demonstrated in your own bathtub. Get a shallow
aluminum container and load it with something, say washers, place it in
the water, note where the water line is. Take it out, fill the inside
EVENLY with a layer of floatation material (to simulate an even fill of
floatation that would be in the boat, as described above), punch holes
at the water line, put the load back in (evenly distributed to avoid
tipping), put the whole thing back in the water and flood it. The pan
will sink to a waterlogged condition, but will gradually rise as the
water drains out of the previously punched holes. Bear in mind that the
boat will be very much more stable than a pan due to the keel. The rate
of recovery of course will be a proportional to the rate of flow through
the drains.
Having said that, all these good things are predicated on not going
turtle, or being able to right the boat having done so. Hence the other
comments about floatation at the top of the mast and being able to
reverse a jackknifed keel. However, I fail to see how putting floatation
material as I have described would make the boat any more stable in a
turtled position than does the existing floatation.
The reason for adding material under the cockpit seats is not to make
the boat more unsinkable, but to provide less volume for water to fill,
thus the less water to drain out.

Bernie. "HMS Pinafore"