[PSUBS-MAILIST] Diver lockout VBT

[Rob Bryan <Sundiver2000@earthlink.net>]

I've no experience with sub lockouts. I would think lockouts while 
hovering would be very difficult and dangerous, so assuming sitting on 
the bottom...

Getting in and out of a vertical hatch with gear on is quite a task, 
whether scuba or line (with a bailout). In dive bell lockouts, the bell 
is flooded a little to make it easier. Wouldn't you do that in a sub 
lock out? So if the lock was 48" in diameter and you only flooded it up 
a foot, that would be 800 lbs. The diver leaving would be negligible, 
no? (this doesn't even include any trunk volume). Is this actually a 
problem?
Rob B

ShellyDalg@aol.com wrote:
> Hi. This is in response to the diver weight compensation question.
> Every dive trip in your sub requires careful measurement of what you 
> bring on-board.
> If the dive plan calls for a diver to exit the sub while at depth, I 
> would think that it would be better to add buoyancy to cover the 
> divers extra weight while on-board, and then dump that buoyancy ( air 
> bubble ) when the diver exits the sub, there-by maintaining neutral 
> buoyancy while the diver is outside.
> When the diver is back on-board, blow the required amount of air back 
> into the trim tank ( a measured amount of water to compensate for 
> exactly how much the diver weighs ) and again maintaining neutral 
> buoyancy.
> A sub with a diver lock-out function would need a bigger trim tank 
> than a sub without that capability.
> Don't forget to calculate how much air the diver displaces with his 
> body, as this will figure into the required additional buoyancy too.
> You don't need a separate pump system, nor would that be desirable, to 
> let a diver exit and re-enter the sub. The lock-out chamber is 
> controlled by air pressure, and any small amount of water that 
> remained within would be easily compensated for by the additional trim 
> tank volume.
> You WILL need some means of dumping the air from the lock-out chamber 
> once the water is blown out and the hatch is closed so the diver is 
> once again  at one atmosphere. This needs to be monitored closely so a 
> diver has time to dump the excess nitrogen absorbed by his body 
> tissues and blood. A diver lock-out chamber is really much like a 
> de-compression chamber, but is located inside another chamber ( the 
> sub's pressure hull ) so a compressor to drive out the additional air 
> is required.
> Frank D.
>
>
>
> ------------------------------------------------------------------------
> See what's free at AOL.com 
> <http://www.aol.com?ncid=AOLAOF00020000000503>.



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