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Hi Vance,
I thought the K250 would be about 5 times
that volume.
If I knew the length & diameter of the hull I
could roughly work it out.
The problem with the flow calculation is the
pressure will be at 100 psi
or there abouts to begin with & then diminish
to virtually no flow as the
pressure equalizes. I'm no good with those sorts of
equations.
At that point the air in the hull will be squashed
to 1/8th
its initial volume.( about 13% of the hull volume )
I can imagine lines painted on the inside of the
hull with FILL TO HERE 200FT
written next to them.
Alan
----- Original Message -----
Sent: Sunday, August 22, 2010 4:52
AM
Subject: Re: [PSUBS-MAILIST] Scuba tank
hook up
The K-250 displaces about 2500# or just under 40 cubic feet. 7 1/2
gallons per cubic foot, so that's.....um.....300 gallons or so? All you need
is GPM through a 2" ball valve at 100 psi or a little better (assuming near
maximum depth) and you'll have minimum flood time. A quick look on the web
shows a 127 gpm for that size valve up to 100 psi, so your flood time would be
2 1/2 minutes or so, assuming all those numbers are somewhere in the ball
park. That doesn't take into account the piping and any fittings (say, a
strainer externally and an elbow inside to aim the water stream somewhere
besides your back pocket).
Caveat: Don't take any of this at face value. I did it in my head which
is, as my children will attest, about half full of.....well, something besides
brain matter.
Vance
-----Original
Message----- From: Alan James <alanjames@xtra.co.nz> To:
personal_submersibles@psubs.org Sent: Fri, Aug 20, 2010 10:09
pm Subject: Re: [PSUBS-MAILIST] Scuba tank hook up
The first question is..... What is the internal
volume of a K250 ?
The second is..... What happened to Sean
Stevenson; he seemed to
be able to give flow calculations off the top of
his head.
Alan
----- Original Message -----
Sent: Saturday, August 21, 2010 1:24
PM
Subject: Re: [PSUBS-MAILIST] Scuba tank
hook up
It shouldn't be that hard to figure. Some tank manufacturer or
supplier probably has a gallons to level chart of some kind. George called
for a 2" ball valve for flooding, Flow rates should be available from
a valve manufacturer, maybe on an x-y plot with flow versus pressure. I'll
bet flooding will be faster than you think.
Vance
-----Original
Message----- From: Alan James < alanjames@xtra.co.nz> To: personal_submersibles@psubs.orgSent:
Fri, Aug 20, 2010 7:58 pm Subject: Re: [PSUBS-MAILIST] Scuba tank hook
up
Hi Vance,
Below is a quote from a 1970s paper Phil
presented on sub escape.
It agrees with what you are saying about
differing scenarios & " one
size doesn't fit all". I'd like to see a white
paper on K250 escape covering
best proceedure for different depths maybe from
100 to 250ft & for 1, 2 or 3
people. However I couldn't find a flow
calculator so I don't know how long
a K250 would take to flood to various internal
levels.
Alan
There are at least five major factors to
consider in programming emergency procedures:
A) Nature of the problem (e.g. is the SDC entrapped?)
B) Depth of water (e.g. possible to use standby
diver?)
C) Umbilical condition (e.g. severed or intact?)
D) Load line condition ( e.g. severed or intact?)
E) SDC pressure condition (e.g. pressurized
or unpressurized?)
If one fixed case is assumed for question
"A" - the SDC is entrapped - the critical examination
of the possible combinations of other
factors will require a detailed analysis of at
least sixteen possible situations and the calculation
of the most effective emergency procedures
to use in each case.
Some time ago, our firm undertook the task
of reviewing SDC emergency procedures and we
were, frankly, astonished at the number of
possible situations that had simply not been
considered previously. The procedures to cope
were equally obscure and detailed searching of
existing literature confirmed this general lack
of specific consideration. We have since been
continuously involved in compiling emergency
procedures and running field tests on various
safety devices, both SDC internal and external.
The length of this discussion is not sufficient
to describe, in detail, the total findings, but
some highlights are presented for consideration.
It should be heavily stressed that the described
approaches should in no way be considered
universal panacea's to the problems, but
merely as potentially useful alternates to current
practises.
----- Original Message -----
Sent: Saturday, August 21, 2010 10:35
AM
Subject: Re: [PSUBS-MAILIST] Scuba
tank hook up
I see what he's talking about. A controlled flood and then
equalization with your onboard air supply. Good stuff, especially with the
dome/elevator arrangement--sort of a rigid steinke hood. Very clever, but
only useful when you've got the dome blown, the straps tight and are ready
to haul-ass for the surface. I was thinking about a flooded or flooding
boat in an unassisted blow and go scenario with possibly two people to
deal with.
Vance
-----Original
Message----- From: Alan James < alanjames@xtra.co.nz> To: personal_submersibles@psubs.orgSent:
Fri, Aug 20, 2010 6:05 pm Subject: Re: [PSUBS-MAILIST] Scuba tank hook
up
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
----- Original Message -----
----- Original Message -----
Sent: Saturday, August 21, 2010
1:25 AM
Subject: Re: [PSUBS-MAILIST] Scuba
tank hook up
Alan,
I must be missing something here. What is the last 15% of the
volume in a flooding scenario? I've never had to do it, but flooding the
boat equalizes pressure inside and out. The volume of air compresses in
a high point to that same pressure. All you would need was a BIBS and a
face mask or something. No increase of pressure inside would be
necessary unless your intent is to maintain a larger air bubble inside
the boat, which would be dangerous unless you happened to have a bottom
hatch (assuming the boat is in an attitude where it could even be
used).
One caveat about air in the boat that I do know about is the
violence of that bubble's release when the hatch is opened. In the
Nekton Beta accident, the bubble shot Rick Slater out of the boat like a
cork out of a champagne bottle, and the sudden movement of water
flooding in to replace that air is probably what caused the other
passenger to bang his head, which either caused directly or contributed
to his drowning at depth. Based on that, it seems that a larger bubble
might very well cause proportionally larger problems.
Mind you, flooding the boat is a pretty big problem all by itself.
It gives me the shivers just thinking about it.
Vance
-----Original
Message----- From: Recon1st@aol.comTo: personal_submersibles@psubs.orgSent:
Fri, Aug 20, 2010 8:53 am Subject: Re: [PSUBS-MAILIST] Scuba tank
hook up
Alan I would not use air to equalize in an emergency. I
would simply open my flood
valve and let the incoming water do the job. This would
allow time to equalize your
ears and such. And the volume of air exploding from the
tower is much less violent.
Personally I prefer to have full pressure to the hull and
regulate it inside. In all scenarios
I can think of, a high flow is not needed. Filling tanks
and such, a slow fill seems to be
much more controllable.
Dean
Hi Dean,
I've got more questions than answers here.
If we use air to pressurize the last 15% of the sub volume in an
emergency escape,
wouldn't it be better to have the full pressure of the tank
coming in through the hull?
I googled but couldn't find anything on the flow rate of air
coming straight out of a
scuba tank compared to what it might be coming out of a first
stage regulator or
your 250 psi regulator. ( I guess hose width figures in the
equation.)
I did open up my dive tank into a rubbish bag & it blew it up
about 4 x faster straight from
the tank at 3000 psi than from the 2nd stage purge valve.
In the case of a 200ft deep escape your 250 psi regulator would
be operating at 150 psi
above the ambient pressure required in the hull to do the final
equalization. Having a faster
fill might make the difference between getting the bends or
not.
Alan
----- Original Message -----
Sent: Friday, August 20, 2010
6:55 AM
Subject: Re: [PSUBS-MAILIST]
Scuba tank hook up
Sorry for the omission. The Tanks will be external and
all I would need is HP. I have
regulators inside and the ability to crank em up to 250
psi. I guess what I am looking for
is yoke type with out the regulator.
Dean
In a message dated 8/19/2010 11:26:37 A.M. Central Daylight
Time, vbra676539@aol.com
writes: External or internal? And are you set up for high pressure
or not? HP air can be had with a simple yoke (like a first stage
without the regulator). If you need lower pressure, then the first
stage will work fine. George carried his internally, which was an
issue at depth because scuba first stages can only be cranked up
to about 150-160 pounds. Externally, you get that over ambient,
which gives you full flow. The only other issue is flow. The 1st
stage arrangement is pretty slow.
Vance
-----Original
Message----- From: Recon1st@aol.comTo: personal_submersibles@psubs.orgSent:
Thu, Aug 19, 2010 12:03 pm Subject: Re: [PSUBS-MAILIST] Scuba
tank hook up
What have any of you done to hook up
standard SCUBA tanks for HP air source.
Originally I was using a large steel
tank. It is just too heavy to handle and I
am
switching to twin Aluminum 100
tanks.
I am thinking a scuba first stage
regulator is used with an adaptor at the thru hull
connection.
Appreciate any
help
Dean
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