Re: [PSUBS-MAILIST] VBT positioning

[VBra676539@aol.com]

In a message dated 7/16/2001 2:07:17 AM Eastern Daylight Time, 
vulcania@interpac.net writes:

<< P.S. to previous message:
 
 Anyway, my point was to show that external ballast tanks add their
 displacement to that of the pressure hull and factor into the total
 displacement of the boat, while an internal ballast tank does not.  Hope the
 math error in my examples (now clarified) didn't throw you off.
 
 Pat
 
  >>
Pat,

I was hoping you'd get around to saying this, as I think it answers the 
original question. Hard (pressure resistant) variable buoyancy tanks, whether 
mounted inside or outside, vent overboard. Soft tanks are filled using 
ambient pressure as the motive force and vented inboard (no other way, is 
there?) then pumped overboard. And there are a couple of interesting 
variables, including a pressure compensated, externally mounted hard system 
which allows you to use a much lighter SS or aluminium (that's aluminium for 
you, Harry) tank or tanks.

Either way, the term Variable Buoyancy Tank (VBT) is commonly used, and means 
what it says. It is a system for altering the sub's buoyancy without changing 
it's weight. And keep in mind that hard tanks are positive and quick for 
those changes and soft systems are generally very slow and very precise 
(relative to the former).

Best Regards,
Vance