Re: [PSUBS-MAILIST] Escape from a K250 at 200 ft

Hi Alan,

Thanks for putting the time into those calculations. It is very interesting to think about the fact that the flood rate will be decreasing as the pressure in the hull gets closer to ambient.

It makes me think that to reduce the initial increase in pressure to a tolerable rate; the pilot can do one of two things:

(1) Just crack the flood valve at first, then full open as the sub fills. This option would require access to the valve from the hatch area.

(2) Install two smaller flood valves instead on one big one. Open the second valve as flooding slows down. The second valve could be placed in the hatch to double as a vent valve to release the bubble of air that remains.

Phil made a good point about being able to think when the narcosis hits. Makes me think it might be a good idea to carry a bail out bottle of mixed gas just in case you get stuck below 100 ft.

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 Alan James
Sent: Tuesday, August 24, 2010 4:06 AM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Escape from a K250 at 200 ft

Hi all,

I've put some facts & figures together re flooding a K250 at 200 ft.

Firstly, sorry I move between metric & imperial. I was brought up on

imperial then N.Z. moved to metric. The metric system is great for these

soughts of calculations.

The first assumption is that the hull & hatch area displaces 1,100 liters.

The hatch 100 liters & the hull 1000 liters.

The flow figures through a 2" pipe come from table 2 on this link. It was the best I could find.

http://flexpvc..com/WaterFlowBasedOnPipeSize.shtml

These figures are approximations as the flow rate changes all the time. Also I'm not

taking into account how many or how fat the occupants are.

To fill to half way with the 2" valve at 100 psi the water will be coming in at 384 gallons per minute.

It will fill the 550 liters (132 gallons) in about 20 seconds. The air in the hull will be compressed

to half its size & will be an equivalent pressure (14.7 psi) as at 33 ft.

To fill the hull from 1/2 to 2/3 the flow pressure will be between 85 psi & 70 psi. About 340 gpm.

The volume to be filled is 183 liters ( 48 gallons ).This will take 8 &1/2 seconds. In terms of internal

pressure you have just gone from 14.7 to 29.2 psi wich is the same as diving from 33 ft to 66 ft in

8&1/2 seconds.

To fill the hull to 3/4 the pressure will be from 70 to 55 psi about 300 gpm.

The volume to be filled is 92 liters ( 24 gallons ). This will take about 5 seconds. Again this is

equivalent to going down another 33 ft. to 99 ft.

Am being kicked off the computer for the night so will leave it there.

But that is flooding so fast, I'd want to have my hand on the valve as at that rate you'd blow

your ear drums for sure. It's best to equalize your ears before they start feeling pain & in this

instance you can't reverse the pressure like while diving, by ascending.

These figures are open for correction.

Regards Alan