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Re: [PSUBS-MAILIST] escaping from a K250 at 200ft



Thanks Phil good stuff,
Yes I made a miscalculation thinking ambient pressure rather than the pressure from
the compression of air in the hull.
So if you were filling the last 15% of a 4 tonne sub with air you'd need to leave yourself at least
2,400 liters of air.
Using the dome  to go up is a great idea. Especially the diminishing pressure in the air pocket
enabling breathing & eliminating the chance of an embolism. Also you at least get your dome / hatch back.
Most existing boats won't have an internal hinge; do you think a small parachute arrangement
would work similarly? Maybe have a stiffened or inflatable ring at the skirt of the parachute that
can be jammed in the hatch entrance. I'm not sure how a hinged hatch would behave at the moment it
opened, whether it would open & close as air belched out & whack you on the head.
Appreciated the bit on nitrogen narcosis; I had had thoughts of using an external scuba tank to go up with,
but your comments put paid to that.
Regards Alan
 
----- Original Message -----
Sent: Sunday, August 08, 2010 1:06 PM
Subject: Re: [PSUBS-MAILIST] escaping from a K250 at 200ft

Hi, Alan
Yeah, we ran the 'pressure up and escape' numbers for the micro sub 'Sea Urchin' some years ago. As I recall, escape from the rated depth (350') was quite practical. As a rule of thumb, you save your ballast air (and 02) for the final blow. The speed of initial filling is not as critical as the last few minutes before the entry dome/hatch comes off. You have to remember that when your sub is half -full of water, you are only at 33 feet of pressure (29.4 PSI), when it's 3 quarters full, you're only at 66' and so on. My plan on the Sea-Urchin was to have the hinge on the inside with the ability to pull the hinge pin out so that the entry dome is held on only by water pressure - we planned to have two 'armpit slings' stowed in a small package that is easily opened - and the sling ends were to be affixed to the inside of the dome seat ring. The procedure for bail out was to get a reading on the volume of the ballast air (by supply gauge) left, flood up with water until either the time was beginning to exceed the no-decom table (the depth IN the sub, not ambient depth) or you had flooded right up. Probably, you'd blow the last 10 or 15 % by air, Make sure the slings are firmly attached and blast in the air! The dome/hatch achieves lift-off with your head and shoulders in the gas bubble of the dome, your body acts as the drogue to keep the dome from tipping, you are breathing constantly-refreshed air (and avoiding embolism, therby) as the gas expands and bubbles out - you hit the surface and duck out and then yank on your Mae West cord to inflate your life-jacket and await pick-up by your chase boat (or commence floundering towards shore if you were subbing with no surface craft in attendance).
 
The numbers indicated that the likelihood of bends was very low - since your exposure to full depth is extremely brief. We were more concerned about the instant hit of hp nitrogen to those not accustomed to deep gas change-overs. It can be quite . . .err. . .'startling'! Hence the snugged-up slings- rather than internal handles ( my first thought) - even if you're narked out of your skull at the onset the slings will hold you in position until your calm. cool thoughts return. Actually, though, those stalwart psubbers who are also tech -divers will recognize that the likelihood of bad narcosis trip from this very brief 'deep air dive' is even less than the bends (according to the work done by researchers Overton and Mayer on the oil/water solubility ratios and the time required for the combination of Co2 and N2 to act.
    I had developed a bubble stage called the 'Newt-Chute' as a safety refuge and self-rescue/self-decom vehicle for deep Heo2 bounce diving - which we (OII/Can-Dive) were doing a lot of at that time (in the early 70's) I gave a paper at the Offshore Technology Conference titled "Diving Bell escape systems - some observations and test results) Perry started building and selling these bubble stages shortly after that and then COMEX after them- and they became known in the industry as  'Class 2 bells'). While testing the Newt -Chute, the dome-lift to the surface occurred to me and we tried it in several different configurations and it worked fine. More than a decade later we re-purposed the idea to sub escape.
Sorry for such a  long answer, Alan.
Phil Nuytten 
----- Original Message -----
From: Alan James
Sent: Saturday, August 07, 2010 3:48 PM
Subject: [PSUBS-MAILIST] escaping from a K250 at 200ft

Hi All,
I know escaping from a sub has been discussed before, but has anybody crunched
the numbers to see if it's possible from a depth of say 200ft in a K250 or 350.
How long does it take to fill the hull with the flood valve? The water would be coming
in at 100 psi but this pressure would diminish progressively as the hull filled. At 3/4
full it would be 25 psi. At what stage would you start adding compressed air
to help with the equalization of the hull & how much air would you need & how fast would
it flow in?
If you filled your ballast tanks with air to try and escape an entanglement first you might
not have enough left to help equalize the hull.
When the flood time is known, how saturated with nitrogen are you & what are your chances
of surviving the bends if you opened the hatch & went straight up?
If this was pre calculated it might be concluded that a scuba tank (or 2) was needed & decompression
stops at varying depths & times were necessary.
I don't know the internal volume of a K250, I think the flood valve is 2"
Regards Alan