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

I have just done a tentative calc showing that to meet Greg’s maximum rate of descent and looking at Sub volumes of 90, 150 and 200 cu ft at increasing depths of 50 ft the following chart is the maximum valve size for flooding at those depths.

This shows that for a K350 at 350 ft depth a ½” valve would be maximum for flooding to avoid the last 50% of the sub flooding too fast. DO NOT TAKE THIS AS GOSPEL. This was a quick exercise for discussion purposes.

What did become apparent was that by using these valve sizes you would get into decompression times trying to avoid too fast a rate of decompression. This gives reason to having two valves. One to fill quickly to the 50% bubble line, or more as one may see fit, and then a smaller one to control the rate of

Pressurization.

This has changed my attitude of putting in a 2” valve for a rating of 400 ft although if you get tangled at 100 ft it could be used. Interesting figures and needs further work. Chs, Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Greg Cottrell
Sent: Thursday, 26 August 2010 12:03 a.m.
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Escape from a K250 at 200 ft

I’m a little bit spoiled since my hull diameter is 51” and room is not an issue. Another benefit of the thicker wetsuit jacket is flotation.

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 Hugh Fulton
Sent: Tuesday, August 24, 2010 4:53 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Escape from a K250 at 200 ft

Greg,

Thanks for that info. Now that is useful. Alludes to a remark Phil made on effects of narc in getting out of a sub which is good for blow and go but not much good for 2 or 3 people subs. Does the navy have a rate of filling to accommodate this? That rate of pressurization would mean at least 3 minutes. Is there a paper on the effects of cold on narcosis. What is the effect likely to be? While we can pontificate on these aspects I don’t think we should dwell on them too long and concentrate more on release of entanglement items as Vance has pointed out. As a flying instructor once told me in answer to my question of what should you do if you get into this situation--- He replied “A good pilot avoids getting into those situations” Regarding a wet suit in the event of ------ Is a full 3mm going to be better than a top half 7mm . Space is a premium. Chs, Hugh

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Greg Cottrell
Sent: Wednesday, 25 August 2010 6:56 a.m.
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Escape from a K250 at 200 ft

Maximum recommended safe descent rate for scuba varies depending on the certifying agency but fall between 70 and 80 fpm. Faster than that aggravates nitrogen narcosis. It can also cause joint pain and HPNS.

Another danger escaping from a sub could be shivering uncontrollably in cold water. It happened to me once when I was diving with the FD and it’s something that doesn’t seem dangerous but is when you literally lose all muscle control. A thick wet suit top would probably be a good take along item in cold water.

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 Jon Wallace
Sent: Tuesday, August 24, 2010 12:40 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Escape from a K250 at 200 ft

Hugh Fulton created a "flooding" spreadsheet calculator back in early May of this year. I just checked it and the results for a K-250 type sub at 200 feet with one 2-inch flood valve comes out to total flood in 50 seconds. With one 1-inch valve that time is slowed to 200 seconds, and with a 3/4 inch valve the time is 355 seconds.

I didn't have time to post the spreadsheet before the convention but will get to it this week.

Jon

On 8/24/2010 4:06 AM, Alan James wrote:

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

__________ Information from ESET NOD32 Antivirus, version of virus signature database 5391 (20100823) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

__________ Information from ESET NOD32 Antivirus, version of virus signature database 5394 (20100824) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com