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Re: [PSUBS-MAILIST] K250 to K400 modification
Hi Alan,
it seems this could be "fixed" by not operating the K250
outside of it's operational depth. But I think you are
talking about modifying at K250 so it can rescue a sub at
400feet.
This would mean if there where any problems with the K250+150
then the occupants would be in more trouble than the occupants
of the 400feet sub (which presumably is rated to be at 400feet).
If the K250+150 be came entangled as well, rescuing that
sub would probably have to take priority over the original
SUBDIS. This will also be a more complex, more dangerous
rescue operation, requiring the accent to be very controlled
so excess gas can bleed off. If accent is not carefully
control (for example, a lift bag which is too large is used
resulting an uncontrollable rapid accent) there is the
risk of blowing out the view ports.
I think this method, although it could work, would be too
great of a liability to introduce to a SUBDIS situation.
A side note, the K250 should have been tested to 2x of the 250feet
operational depth (i.e. 500feet), if it was taken to 400feet
"in an emergency", then the test dive would have been 1.25x it's
current depth (which is the minimum ABS recommends)... Still
a bad idea, but rescuing the K350+150 is less complicated if it's
not pressurized. [Note: I am not advocating operating a sub over
it's operational depth.]
I think another way of presenting this discussion is, what
about adding diver lockout capability to a K250, so the pilot
could leave the sub at depths of up to 135feet. Either by
adding a bottom hatch, or flooding the hull (and blowing it
dry upon re-entry).
How we act in an emergency should be with the aims of reducing
the risks we are taking so as to ensure the situation does not
get worse. We should not be introducing additional risk into
the situation in hopes of resolving it. (Or so I think anyway....)
Cheers,
Ian.
-----Original Message-----
From: Alan James
Sent: Jul 4, 2010 2:22 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] K250 to K400 modification
Hi Jon,
The emergency I was thinking of was along the lines
of
a stricken sub entangled at 400ft & the nearest
help was
a sub capable of 250ft depth.
Alan
----- Original Message -----
From:
Jon Wallace
To: personal_submersibles@psubs.org
Sent: Sunday, July 04, 2010 5:41 PM
Subject: Re: [PSUBS-MAILIST] K250 to K400
modification
Sorry Alan, I missed the "emergency situation" part.
So yes, in an emergency where you are sinking in water beyond your normal
operating depth you could certainly counter some amount of outside pressure by
increasing the pressure within. That may delay (possibly prevent
depending upon depth) hull failure but of course has the potential for some
other nasty biological side effects and I'm guessing in such an emergency
you're probably going to be at the increased ambient depth well beyond
no-decompression limits. We had a similar discussion a few years ago
about standardizing on a specific valve so that divers could feed air into the
cabin of disabled sub that did not have life support capability, until that
sub could be raised. I believe the discussion started with "schrader"
valves (tire valves) which were determined to be too small to be useful.
Many of the same issues were raised at that time ie...decompression upon
surfacing, additional pressure in the cabin affecting instruments,
etc.
Jon
On 7/4/2010 12:29 AM, Alan James wrote:
Thanks Hugh & Jon for the vote of
confidance.
I did qualify this with " In an emergency
situation". I think I have been
misunderstood.
You take your sub down to its 250ft limit with
several extra dive tanks on board.
At this point the outside of your hull is
experiencing round 125psi.
For every 33ft further you go down you add
14.7psi. The hull would always be experiencing
125psi from the outside as the pressure you're
adding would be countering the additional
pressure from additional depth.
So no pressure as such from the inside would be
pushing your view ports out.
The reason I said to increase the O2 flow into
the hull is the "bellows add" system based on
sensing a drop in pressure wouldn't work. In
that system the O2 flow is set below the users
normal O2 consumption & then topped up from
the bellows add system because if the O2
was set too high there would be a continual
pressure build up & 02 % increase.
You could safely bump up the O2 a tad as it
would be safer to have too much O2 than not
enough. This, as Jon said wouldn't matter much
because your time would be constrained by
decompression tables, & there would be
enough air in the hull to breath from.
So in a life or death emergency you
could take several air tanks into your hull & a set of
dive timetables, open the tanks by hand at the
250ft mark & go to 400ft.
Alan
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