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I just got back two days
ago from diving Snoopy on a wall in Summersville Lake, WV. Super place, the best
I've ever been to.
When going up and down
you basically have two choices; either trim to neutral on the surface and motor
down, or trim heavy and use VBT at depth to level off (or as an alternative blow
a bubble into MBT). With the K250 I prefer the second method
because I feel the electric power is in shorter supply than the air.
There's only three batteries, and to move vertically I have to
run two thrusters. Plus, I like the quiet. On the next sub,
however, the decision might go the other way because I'll
have 12 batteries and the use of a single vertically mounted
thruster in the center of the boat.
A minor irritant with the
K250 is that when you open the VBT you don't know whether water is going to go
in or out of the tank -- it just depends on how the pressure inside the VBT
compares to ambient, and the pressure inside is not instrumented. I really don't
care about the water level, except to know whether the tank is completely full
or completely empty, and both those conditions are very clearly announced
by bubbles (bubbles out the bottom = empty tank, no more bubbles out
the top = full tank). So rather than worry about the water level in
the VBT, my suggestion for those who want to make an incremental improvement
would be to install a differential pressure gauge that compares VBT pressure to
ambient. It would save air, because you won't over-pressurize the VBT
unnecessarily. And you'll know exactly what's about to happen when you open the
VBT valves.
cheers,
Alec The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it.
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
ShellyDalg@aol.com
Sent: Friday, July 24, 2009 1:28 AM To: personal_submersibles@psubs.org Subject: Re: [PSUBS-MAILIST] water level PART TWO.......
Sorry, I lost my e-mail thing for a minute....Any way, It's not essential
to have a VBT at all, but it makes a lot of sense to include it in your sub if
you're building your own. Just how much VBT is best is another question.
Available room for the tank, and storage of enough HP air to blow it dry
are two things that come to mind right off. How many times you'd need to blow it
out on a dive would dictate how much air you'd need onboard if it was fairly
large and you expected to make adjustments while at depth. It could take a LOT
of air to blow a 40 gallon tank dry at 500 feet!
I would think that most psubbers use the VBT for fine adjustment of
buoyancy, and that is done usually at the beginning of the dive while
still shallow. Then, once the adjustment is made, the tank is valved off, and
remains that way until the dive is over and you're back up near the surface. For
that simple operation, no level gage would be required, ( although it would
still be a great convenience ) and the tank needn't be that strong.
The other options of adjusting at depth would require a much stronger tank
and more stored HP air to adjust it. I guess it depends on how you plan to use
your sub, and whether you wanted or thought you needed the extra option of
deep adjustment in buoyancy. Is it a necessity? or just a convenience. Frank
D.
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