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RE: [PSUBS-MAILIST] Compression Time Tables for Wet Exit
Hi all
I'd be very interested in getting a copy of the escape presentation as well.
I had originally thought i would try and encorporate a bottom hatch in my sub simply for emergency escape means. Tricky on a K350 with limited space, but i think it would have worked. See the drawing i did here. http://www.guernseysubmarine.com/index_files/Page8236.htm
But, as Carsten pointed out, the amount of air you need to carry to fully equalise the cabin to open the hatch is such a lot at any significant depth. And, its a lot more work, so i thought of an alternative.
Ive gone for the removable front dome idea the same as is used on the Nemo Sub.
The idea being that in the event of needing to flood the sub, i would be able to use the following procedure. (assuming the sub is level on the bottom).
1. Leave the hatch secured.
2. Release the dome securing pins.
3. Don my scuba gear.
4. Flood the sub keeping my head in the tower.
5. Wait until the pressure is equalised. I should still have a bubble of air in the tower.
6. Kick out the front dome and swim out.
The idea is that it should in theory eliminate the violent rush of air as the hatch is opened that people have been talking about.
Of course, if something went wrong with that, i would have option 2 of opening the hatch as R/Jay has described.
The other thing i thought i could do is:
Calculate how far up inside the cabin the water will come upon opening the flood valve at different depths (with hatch secured). I could draw on a scale along the inside of the hull so upon flooding i would know "the water should come up to about here" type thing. Just to keep the nerves steadyish as you flood.
James
----- Original Message -----
From: Hugh Fulton [mailto:hc.fulton@gmail.com]
To: personal_submersibles@psubs.org
Sent: Mon, 7 Jul 2008 15:32:48 +1200
Subject: RE: [PSUBS-MAILIST] Compression Time Tables for Wet Exit
Well, there is nothing like experience. Scary stuff. Great to have it from
the horse's mouth so to speak if you will pardon the expression.
Any chance of getting a copy of your presentation? I still haven't finished
my design let alone started building. Been at it for 7 mths so far !!
And yes I can imagine. I was just cleaning out the swimming pool at 10
degrees C and I was thinking that was enough of a problem with only my arm
in it.
Add burst ear drums and loss of where is up and it's a wonder there are any
survivors. Grateful for the explanation. Regards, Hugh
_____
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jay K. Jeffries
Sent: 07 July 2008 14:33
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Compression Time Tables for Wet Exit
Hugh,
It was hard for me to reconcile at first also. It is a density issue the
air being buoyant wants to rush out and it sucks you out with it and it
entrains water with it. I once cracked (fortunately didn't open it fully) a
hatch on a sunken sub at 135 fsw. The ensuing gas escape caused a strong
suctional force upward and resulted in a boil 30 feet in diameter and a foot
high at the surface.pushed the surface support boat back to the limits of
its mooring.
The Brits went back to the Med and tested a later version of their escape
apparatus/exposure suit and broke their record by a short distance. The US
Submarine Service has now adopted the British-style escape apparatus (I
believe the Mk-10) and retired the Steinke Hood which I have previous used
in practice as part of submarine training. It is a rapid express train ride
to the surface!
In my presentation was a table and graph that should for various depths how
long you have to get out of the sub and start for the surface. The deeper
the water, the shorter the time period. You can't realize how debilitating
the temperature of the water can be. Reading accounts of previous escapes
and talking with one of the survivors from the USS Squalus really sinks home
that you want to make your escape efforts as soon as possible if a better
solution is not available.
Something to keep in mind that when we speak of hoods and escape apparatus
from subs, this gear is all made for large subs with dedicated escape
chambers that facilitate using this escape gear. We don't have that option
in most PSUBS.
R/Jay
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Hugh Fulton
Sent: Sunday, July 06, 2008 9:53 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Compression Time Tables for Wet Exit
Hi Jay,
Obviously agree with you on flooding etc and getting out but cant reconcile
with being blown out if the sub was full of compressed air. Just from a
theoretical point of view:- As it would be at same pressure as outside it
would similar to opening the hatch at 2 ft below the surface with just a
huge inrush of water and the problem as I see it would be the same as trying
to exit a toilet bowl while flushed!! ( We Downunder always revert to
toilet humour) However I do remember seeing an escape hood which has been
successfully used from about 600 ft I believe was the figure claimed.
However being a diver myself and having been down to 185 ft with Scuba it's
a hell of a long way up without fins. I would be interested in how the hood
actually functions. I understand it has a small pony bottle but don't know
what capacity.
I think that flooding through a valve would give time to equalize your ears
and provided you had your head close to the top the air would be compressed
by the flooding of the water to the point where you would need to submerge
your head and start with the breathing apparatus. We should work out what
the time frames should be as if the size of valve is stipulated then it
could be worked out. The hood idea is the best as expelled air can be
rebreathed and a constant flow of replenishing would give buoyancy to the
hood etc etc.
Interesting but scary. http://www.silvercrestsubmarines.co.uk/news.html is
the link to see the escape suits.
Just hope we never get into that circumstance.
Regards Hugh