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Re: [PSUBS-MAILIST] Diver lockout VBT
Is it necessary to flood the lockout? Assuming a diver + gear is about 300 lbs
(for twin back gas or commercial gear - rec. gear will be less), that amounts to
less than 5 cubic feet of seawater that needs to be admitted to the lockout to
maintain weight, or ~10 cubic feet for two divers. Instead of completely
flooding the chamber, could you not just keep it dry, save for that 600 lbs of
ballast water admitted when divers exit, and pumped out (or displaced by
increased chamber pressure) when they return? Pressure in the chamber will be
diminished somewhat by the lost volume of the divers anyway, forcing the water
level to rise somewhat - it shouldn't be too tough to adjust the water level the
rest of the way in fairly short order.
Quoting Ken F <syber_psubber@yahoo.com>:
> Hey guys,
>
> Thanks for all the info so far.
> The "chain anchor" method I remember was mentioned by Busby, apparently they
> used it primarily in Ben Franklin to maintain their operating depth. I was
> hoping to be able to facilitate a diver lock-out situation within a column of
> water... what if the bottom is too deep?
> It seems to me that If you're on the bottom and you flood the lockout with an
> extra thousand pounds of water or so, you risk the chance of embedding your
> skids far enough into the bottom to create a sticking problem. I suppose it
> would work as long as you didnt purge the water till the diver was back
> inside. Interesting concept.
> As far as adding extra weight in the first place... and then using air in
> ballast to equalize the weight of an exiting diver..... That would have to
> be sealed VBT ballast wouldnt it? It seems like a safety risk to start out
> overly heavy, with the hopes of regulaing through air, rather than starting
> out as normal, and regulaing using water. But since I've done neither, I'm
> really not sure.
>
> Any thoughts Jay?
>
> Ken
>
> irox <irox@ix.netcom.com> wrote:
>
> I don't think 170-200lbs object leaving the sub would be
> negligible, the sub would float off with out it. Carsten
> suggested a neat way of dealing with that, having a heavy
> chain resting on the sea floor attached to the sub, when I
> diver gets out, the sub gets lighter and lifts a link or two
> off the sea bed. Search the archives for Carsten's original
> email about this system.
>
> Cheers,
> Ian.
>
> -----Original Message-----
> >From: Rob Bryan
> >Sent: May 25, 2007 12:46 PM
> >To: personal_submersibles@psubs.org, underseacolonies@yahoogroups.com
> >Subject: [PSUBS-MAILIST] Diver lockout VBT
> >
> >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
> >> .
> >
> >
> >
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