----- Original Message -----
Sent: Thursday, January 05, 2006 9:05
AM
Subject: Re: [PSUBS-MAILIST] Compressable
ballast tanks
Bill, you have it correct; like a water thank in
a rural home water supply system.
You could use a hand operated pump to move water
in and out of a tank, compressing air as the water goes in, and the same air
would be there to decompress and fill the place where the water has been when
your pumping out. Of course, you would
never be able to completely fill the tank with water but you could easily fill
75% of it.
The same system could be used with a bladder
inside the pressure hull. There would be some compression of the air in
the hull as you filled the bladder, but to adjust buoyancy with
maybe three gallons of water (about 25 pounds) it would hardly be
noticed.
You would need a piston type pump capable
of over coming the pressure of the depth your diving in. And, maybe a
backup pump or carry compressed air to blow your main ballast tanks with
just in case of a pump problem.
Dan H.