Re: [PSUBS-MAILIST] air pressure in ballast tank while surfacing

["Jens Laland" <laland@artematrix.org>]

Marc

** One hazard worth thinking about is that, when pumping out the liquid,
** the air pressure inside the tank cannot be allowed to drop too far below
** atmosphere, as the saddle tank plating would be thin and might easily
** implode. No doubt some sort of equalizing valve was provided.

Actually, during WWI the German navy even performed tests with pulling a
certain vacuum on their ballast tanks prior to open the bottom valves to
(crash) dive. But it turned out that an increase of the areas of the air
vent and bottom valves (and leave the bottom valves open while at sea) was
the most effective way to cut down on the time required to dive (and the
RATIO OF the bottom valve cross-sectional area TO air vent cross-sectional
area MOST OFTEN USED at the time was from 10:1 and up to 13:1).

** Simply divide the buoyant force provided by that tank by the
** area of the air/water interface. Or maybe not so simple, as that area -
** and therefore the required pressure - would change as the tank emptied.

I guess I'll have to do that exercise, and make myself a nice plot showing
pressure versus draft :)

Best regards,
Jens Laland




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