[PSUBS-MAILIST] Bubble of doom

Hi Vance,

You’ve brought up an interesting point about the release of air from a sub during egress. George Kittredge had a similar experience of being “shot out” of a sub (although his sub was full of over pressurized air). I wonder if it might be a good idea to put a flood valve in the hatch to flood a sub completely before getting out?

Greg Cottrell

Project Manager

greg@precisionplastics.com

http://www.precisionplastics.com

P please consider the environment before printing this email

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of vbra676539@aol.com
Sent: Friday, August 20, 2010 9:25 AM
To: personal_submersibles@psubs.org
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.com
To: personal_submersibles@psubs.org
Sent: 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

In a message dated 8/19/2010 6:52:01 P.M. Central Daylight Time, alanjames@xtra.co.nz writes:

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 -----

From: Recon1st@aol.com

To: personal_submersibles@psubs.org

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.com
To: personal_submersibles@psubs.org
Sent: 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