Jens, The air pressure will be at the most 2 psi depending where your
ballast tanks are. More like 1/2 psi If your ballast tank is horizontal.
What is the maximum height in feet from the bottom water outlets to the top
of the tank? If that is 2 feet say then the pressure is 1 psi but only when
you have 2 feet of air. It is the differential pressure that you are
concerned with if you are doing a manual pump. If the pump is in the cabin
then you are concerned with the differential pressure between the pump and
the water pressure outside. It is hard to understand where all your
components are and why you are trying to hand pump the air. You are
describing almost a hard buoyancy system but with soft buoyancy tanks. Does
not compute. Sorry I must be missing something. Hugh
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jens Laland
Subject: RE: [PSUBS-MAILIST] air pressure in ballast tank while surfacing
Hugh
Thanks for your respond!
In this design exercise I'm considering a ballast tank system that vents
to atmosphere to dive (thereby allowing water to enter through open bottom
valves).
So, I guess my first answer is: Soft Buoyancy.
Second answer: I will use a water/air vent size (area) ratio of at least
10 to 1 (i.e. water valves many times bigger than the air vents).
The actual size of these water valves will be determined by the design
minimum time to dive (less than 1 minute, maybe as low as 30 seconds). The
ability to crash dive is something I consider to be a safety issue (to
avoid collision at surface).
I'm sorry... I got carried away.
My original question about how to calculate air pressure inside ballast
tank(s) relates to the following scenario:
1) Using a minimum of stored hp air to blow ballast tanks such that the
boat "just manage to surface".
2) Use a manual air pump to displace the remaining water out of the
ballast tanks.
Paragraph #2 is actually what this is all about.
I need to estimate the air pressure inside the ballast tanks with the boat
barely floating on surface... to find the right kind of manual air pump
(if any) that would do the job?
Best regards,
Jens Laland
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