Re: [PSUBS-MAILIST] VBT's

[Rob Bryan <Sundiver2000@earthlink.net>]

I'd certainly agree. A surge could roll the boat and burp air midwater 
or come back down on the diver on the bottom. It needs to be very stable 
and heavy. Put bubblers in the feet if you're worried about getting 
stuck. Frank's point about it being a decompression chamber is a good 
one. Decompression needs to be managed from outside the lock chamber or 
at least over ridable. A small compressor would be necessary to 
depressurize the lock (or a trip to the surface along the decompression 
schedule). If the sub is so small (displacement wise) that this is an 
issue, I'd say locking out would be a very high risk operation.
Interesting topic.
Rob B

vbra676539@aol.com wrote:
> We've been through this. no, No, No, NOOOOOOO!!!!! The boat WILL NOT 
> be neutral, or even close to it while a diver is outside. Live 
> boating, as moving the sub while the diver is outside is called, is 
> strictly forbidden by insurance companies, commerical dive procedures 
> and common sense. You build the boat to flood negative in excess of 
> the BOTH diver's weights, as your tender may in fact have to get out 
> to serve as rescue or back-up diver. Mid-water diving??? Sheesh! Come 
> on, guys. Vance
>
>
> -----Original Message-----
> From: ShellyDalg@aol.com
> To: personal_submersibles@psubs.org
> Sent: Fri, 25 May 2007 12:51 am
> Subject: Re: [PSUBS-MAILIST] VBT's
>
> 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>.
> ------------------------------------------------------------------------
> AOL now offers free email to everyone. Find out more about what's free 
> from AOL at *AOL.com* <http://www.aol.com?ncid=AOLAOF00020000000437>.



************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 53
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************