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RE: [PSUBS-MAILIST] Ambient Variable Ballast Tank
Hi Jon, Ian,
I used a system like Ian describes and have been very happy with the
results. My sub has fore and aft plastic tanks in the pressure hull that are
shaped to fit areas in the hemispherical heads that would be difficult
spaces to use otherwise (they actual create places to sit). The tanks are
"soft" and hold ballast water that is pumped (or sometimes dumped) out after
a dive. My sub is a three seater and I need a lot of variable.
This is not a new idea- the same system was used in at least some of the
Perry subs. There is a picture of this is Busby's book- basically a soft
"pillow tank" under a floor board that could be emptied with a hydro-pump.
Ben Franklin also had a system very similar- bulkheads that form soft tanks
in the fore/ aft hemispheres.
I have to say that I'm not really a fan of using external "bubbles" as a
variable system for P-subs. In my opinion, you can adjust buoyancy this way
in subs that operate at great depths (hundreds of feet) because the air
bubble volume does not change greatly at those depths when ascending or
descending. However, this volume CAN vary greatly with depth changes when
operating in shallow water (less than 100 ft). It's like trying to scuba
dive with air in you BC. Frank Busby once said to me "you can get in TROUBLE
with a BUBBLE".
If you decide to use a pressurized (hard) VBT (Kittredge style) a fiberglass
forklift tank works well and already has the right number of openings. Most
of them are rated for a max working pressure of 294 psi. They never rust,
and, as an extra benefit, you can see through them.
Cheers!
Greg
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of irox
Sent: Friday, May 25, 2012 1:36 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Ambient Variable Ballast Tank
Hi Jon.
Sounds like it might end up being similar to the buoyancy control system
of a sport sub (or some other ambient sub)?
In a similar vein, I was wondering about replacing the VBT with a
soft/flexible bladder inside the pressure hull, and an electric pump
to adjust it (at or close to the surface only). This may make it
easy to switch between one and two man mode, also the bladder could
be a kind of cushion to lie on. It should only need adjusted close
to the surface, once set it shouldn't need changed during the dive.
Cheers!
Ian
P.s: Thanks for fixing the subscriptions problem!
-----Original Message-----
>From: Jon Wallace <jonw@psubs.org>
>Sent: May 24, 2012 10:10 PM
>To: personal_submersibles@psubs.org
>Subject: [PSUBS-MAILIST] Ambient Variable Ballast Tank
>
>
>I had a thought about VBT's today and not sure if we've discussed this
>before. While it seems technically feasible I'm hoping other minds will
>set me straight if I'm heading down an errant path. The problem is the
>size and weight of a VBT made out of steel as in the Kittredge subs.
>They are relatively small but also relatively heavy, and so the net
>buoyancy is rather small, on the order of about 50 pounds. I started
>thinking like Alec with his K-250 and figured for the benefit of only 50
>pounds it likely is not worth the effort of rebuilding and putting that
>VBT back on the 600 and I'd be better off just transferring lead as
>necessary. Now I'm wondering if an ambient VBT would be feasible. Use
>lighter material for the VBT (pvc pipe?) and an air compensated system
>to adjust the internal pressure to always match water pressure. What
>are the pitfalls of such a system?
>
>Jon
>
>
>
>
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