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variable ballast

Ray,
	I had an interesting observation from Dom Liberatore the other day.  
We were talking about the PC-1204 Clelia that HBOI operates.  Dom has 50-60 
dives in it, and hundreds in the JSLs.  I asked how he liked the 12-boat, 
feeling kind of sly because it does a number of things much better than the 
Sea-Links.  He fooled me and immediately responded by complaining about the 
12's deathly slow trim system.  I hadn't thought about it in years, but it 
made me wonder what the psubbers were using.
	My K-boat uses a single hard tank, valved top and bottom with a 
compensated low pressure air source Teed in behind a check valve.  Open both 
valves to flood, close when trimmed and then pressurize the tank to 125 psi 
over ambient pressure by opening the VBT air supply valve.  If you need to 
trim, you valve the air off and open the top (vent) valve to relieve air 
pressure and bubble a little water in for additional weight--or merely crack 
the flood (lower) valve and allow the overpressure to expel some water (or 
blow dry if you've a mind).
	The JSLs use a similar system, only they use air operated valves of 
HBOI design and manufacture.  The adjustable-over-ambient pressure is handled 
via an externally mounted regulator.  The tanks are vertically mounted, 
tubular units, flat ended, and are integral to those enormous main ballast 
tanks.  Vent and fill is very quick.
	Dom's complaint about the 12-boat was the Perry-style variable trim 
system which is composed of a valve manifold, 2 fiberglas tanks and an 
electrically driven positive displacement pump, all mounted internally.  It 
is pretty quick to take on water, but the vent/fill lines are only1/2" 
stainless, not the 1" aperture air operated valves the JSLs use, and to pump 
out, well, it takes awhile, to be kind about it.  And in 1000 feet of water, 
it takes a LONG while.
	The beauty to George Kittredge's dirt-simple VBT and the only 
slightly more ornate Johnson Sea-Link variant, is their speed and lack of 
moving (or electrical) parts.  I am wondering what the rest of you 
mad-hatters have used, or are planning to use.
	And besides, I'm tired of talking about batteries .... for now.
Regards,
Vance