Re: [PSUBS-MAILIST] Main ballast.

[VBra676539@aol.com]

Ray,

This is ONE style of vbt. A hard tank, air-operated, must indeed be a pressure vessel able to withstand the same forces (or more) that the pressure hull does. Harbor Branch, however, uses air compensated vbt's with great success. It isn't all that complicated. You mount them outside and use a regulator to adjust the internal air pressure, maintaining a couple or three hundred pounds positive over ambient to blow tanks with. It takes larger volumes of stored hp air, but is very quickly adjustable and does not need batteries, pumps, switches, manifolds, et al to function.

Beyond that, you can have soft tanks internally, which would be flooded using outside pressure with the tanks venting to atmosphere and pumped overboard as needed. This is a very precise, albeit slow, system. And before anyone asks, the process does not add much overpressure to the internal atmosphere, which is vented overboard in any case, through the cabin vent after surfacing (or overboard in the case of internal pressure, through a check-valve).

Best Regards,
Vance