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Hi Vance,
Filling the last 15% was from Phil Nuytens reply to
my question about escaping from a K250 at 200ft.( rest of my email continued
below)
Also Jay had mentioned this.
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
With regard to filling the sub completely with
water; wouldn't it be slower & slower as you approach the point where the
sub was equalized
& the hatch could be opened. Initially at a
200ft depth the water would be coming in at 100 psi, then when the hull was at
half full the air inside
would be compressed to half its volume so the water would be coming in at 85 psi. At 3/4
full it would be coming in at 60 psi, but eventially to
get the last bit of equalization it would be flowing in at round 1 psi.
If you were deep enough the slow fill may cause you
to get the bends or prolong a session of nitrogen narcosis.
Maybe someone that's good on flow calculations
could do the numbers for a K250 boat so everyone with one will know
exactly
where they stand in an emergency at different
depths.
Regards Alan
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