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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
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