Re: [PSUBS-MAILIST] variable buoyancy

["Rick and Marcia" <empiricus@telus.net>]

If I remember correctly, Phil uses a hollow, metal pilot's seat as the trim
tank in the DeepWorkers.  It sure saves room.  It may be a little cool on
your butt, however.

Regarding the VBT, I agree about the tradeoffs.  The VBT adds complexity but
gives you the option of relative hands-off trim control, ESPECIALLY in
shallow depths.  Always tending depth trim would drive me nuts.  As the mass
of a heavier sub is slow to respond, adjusting trim with the mains may be an
exercise in frustration.  Worse than yo-yo dieting.  But, as the guy in the
field says, it's worked for him, especially when neg. buoyancy was
consistently required, and, not at shallow depths.  But, trying to cruise
off the bottom in fairly shallow water?  Maybe go with the VBT's.

Rick L
Vancouver


----- Original Message -----
From: <vbra676539@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Saturday, December 30, 2006 1:44 PM
Subject: [PSUBS-MAILIST] variable buoyancy


> Dean,
>
> You are quite right. A small bubble will work in one of the MBTs. However,
your double valve idea is over-complex. We did very much the same thing on
the professional circuit using just the 1/4" ball valve on the panel at 2250
psi, and it worked fine--just give her a little squirt. It takes a practiced
wrist, but you'll get the hang of it pretty quick. We had trim systems (on
the Perry boats) which we usually set slightly negative and left alone, then
when we got to wherever it was we were going, I could squirt some air into a
tank and go neutral. The nice thing is that you can go negative again very
quickly, just by opening the big valve and venting that bubble, or part of
it. Keep in mind, actual operations is about staying near the work, whether
in the water column, or on the bottom.
>
> Having said all that, I also operated Aquarius for two seasons with Hyco,
and they had, in fact, stripped the original VBTs out of the boat so all we
had to go on were lead weights for coarse adjustments and air in the MBTs.
It meant that we had to run the boat negative (with MBTs flooded) ALL the
time, and use the mains to go neutral. That worked fine, once I got used to
it (and probably STILL works fine, as I don't see any trim system on the
current iteration at Nuytco). And guess what? It cut a whole system of
valves and operators and tanks out of the boat. That's a bonus, when you can
get away with it. It was a pain in the ass from time to time, but worked
mighty well most of the time.
>
> As a sidenote, I did surveys and light work stuff in that little thing
from the surface to the bottom, in all kinds of weather, and it did
everything I ever asked it to. AND, if anyone asks, a 48" diameter hull is
about perfect for two grown-up children to work in. We could lay down, sit
up, stretch out, pee in peace and didn't even kick each other very often. I
consider 42" about minimum for comfort, which is why we all sit up in the
Ks. There just isn't any room to do anything else.
>
> Phil Nuytton has carried all this a bit further, using a small internal
flood tank of captured water (in an external bladder) to trim neutral on
each dive. That way you don't have to tote lead, and you can STILL blow air
into the mains for positive buoyancy if you need to. And once your trim is
in the onboard tank, you can leave it for the next dive, and the next. When
the next pilot hops in, you shift the water back to the bladder and he goes
through the same process, tailoring the trim to his weight and preference.
>
> The only real issue for our psubs that I see is shallow water ops. A MBT
bubble expands really fast in just a few feet, and you'll have to be quick
to control it. Otherwise, who cares? Folks on the psubs site worry about
this a lot, but you can trust me on this. A ton or two of submarine (never
mind eight or ten tons!) just doesn't react all that fast to a few pounds of
buoyancy either way. Any pilot worth his salt (and you get salty in that
pilot's seat, it's really the only way) will be able to control his (or her)
boat just as well with the mains. VBTs are fiddly, very handy for minor
adjustments, but not terribly useful otherwise.
>
> It's nice to be able to do EVERYTHING in a sub--and flooding a little
water in or pumping it out is a good thing. A very good thing. But there are
trade-offs. I'm overhauling a K-350 as we speak, and the VBT is about rusted
out. I've got to make some decisons along these lines myself. I'm going to
put some kind of VBT in, just haven't decided whether hard tank or soft tank
inside with a pump. I just can't help but remember how sweet it was when one
of the boats was perfectly trimmed--you could steer the thing by leaning
from side to side, and it didn't take any effort at all to steam along doing
video surveys of pipelines or rig bases or whatever. Mostly that kind of
thing takes a good variable ballast system.
>
> Now, you've got lots of answers, but no solutions. Sorry, that's kind of
how it works. Given the room, the money and opportunity, I'd opt for a VBT.
But if it worries you, then launch without the silly thing. You can always
cuss me later and put one in. T'ain't like the ABS is going to come knocking
on your door, is it?
>
> Happy New Year,
> Vance
>
>
> -----Original Message-----
> From: Recon1st@aol.com
> To: personal_submersibles@psubs.org
> Sent: Sat, 30 Dec 2006 12:03 PM
> Subject: Re: [PSUBS-MAILIST] K350 Parts
>
>
> I have read many posts discussing secondary bt
> for fine neutral control.
>
> My question is can't the mbts be used for this?
> It seems to me it could be done by using a simple
> method.
>
> my thoughts are to put 2 inline control valves on the
> hp air line. the valve closest to the mbts would be left
> open and the 2nd one would operate normally. Then
> when fine control is needed, you would close the front
> valve, open the back valve then close it. This would allow
> a small amout of hp air to be delivered giving fine tuning.
> the same could be done on the air release side.
>
> The amount of control would be the volume between the two
> valves.
>
> So am I ignorant again? am I missing somthing here?
>
> just a planning away
> Dean Ackman
> ________________________________________________________________________
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