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
http://www.precisionplastics.com
P please consider the environment before printing
this email
From: owner-
Sent: Tuesday, August 24, 2010
4:06 AM
To:
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.
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