Re: [PSUBS-MAILIST] VBT positioning

["Captain Nemo" <vulcania@interpac.net>]

Hi Martin,

I guess I misread your inquiry about VBT's.  All my references were to hard
ballast tank systems.  Good luck with your project!

Pat

----- Original Message -----
From: "Martin Sanderse" <sanderse@protoproduction.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, July 17, 2001 7:57 AM
Subject: Re: [PSUBS-MAILIST] VBT positioning


>
> ----- Original Message -----
> From: <VBra676539@aol.com>
> To: <personal_submersibles@psubs.org>
> Sent: Monday, July 16, 2001 8:01 AM
> Subject: Re: [PSUBS-MAILIST] VBT positioning
>
> > 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).
>
> With that in mind, I was considering using two bladders, one internal, and
> one external, fluid filled, with a small hydraulic pump operable in either
> direction.  I would of course have to provide limit switches of some sort
on
> the bladders to prevent myself from bursting either one of them.  There
> would be a change in volume inside the hull as the internal bladder filled
> and emptied, but it's a small % of total internal volume.
>
> What I find more problematic is the main ballast tanks for surface
> freeboard.  if I locate them high for surfcae stability, I invariably run
> across the problem where I could trap air somewhere, making it impossible
to
> descend with the VBT volumes I'm thinking of.  If I make the VBT larger,
> then as I decend and rise, the air in the main tanks would compress or
> expand, requiring more VBT adjustments than what seems a stable situation
to
> me.
>
> So far I haven't figured out how to get the main ballast center of
bouyancy
> directly above center without a bunch of valves. (as some appear to have
> done)
>
>
>
>
>
>
> rs
>
>
>
> >
> > Best Regards,
> > Vance
> >
>
>