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Thanks Vance,
My calculations make that 1,173 liters of air in
the hull.
That's 41 cubic feet. Near enough to the 40 you
said.
But it would mean that the K250 would have to be
more than
2,580 lb to sink, wich contradicts wiki's 2,200 lb
for a K250 weight.
Anyway 40 cubic feet is a near enough start
point.
Alan
----- Original Message -----
Sent: Sunday, August 22, 2010 11:07
AM
Subject: Re: [PSUBS-MAILIST] Scuba tank
hook up
All the Ks are 36" OD. A one man 250 has a 48" long hull cylinder and
semi-elliptical heads. Figure 60% of a hemisphere and you'll have the
displacement about right. Plus the conn and hemispherical acrylic hatch (12"
Radius hemi sitting on a four to six inch high cylinder)
-----Original
Message----- From: Alan James < alanjames@xtra.co.nz> To:
personal_submersibles@psubs.org Sent: Sat, Aug 21, 2010 4:55 pm Subject:
Re: [PSUBS-MAILIST] Scuba tank hook up
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.orgSent:
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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