[PSUBS-MAILIST] Ballast Tanks

[Alan via Personal_Submersibles]

Has anybody got an idea or guess as to how much water comes in to
a free flooding ballast tank? Ie. would it fill up to 1/4 of the volume
of the tank with water? And does this vary much after towing.
Also if you know the volume of your ballast tank that would be helpful.
Am considering inlet valves at the bottom of the tanks as I will be towing 
the sub a lot.
Thanks Alan