Brent,
Two things need to be sorted out in this mental exercise.
How many cubic feet of air? Convert this into the weight of the
equivalent volume of water…this is the force pushing up. Now have
many square inches of surface (upward side) is that air applied to? Divide
the force (equivalent pounds of water) by this surface area and you have the
PSI sensed by the interior overhead. As you descend, the bubble gets
smaller is no air is added, buoyancy decreases, and the applied air pressure to
the top surface decreases. Water force inside and out are the same for an
ambient sub.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
Talk sense to a fool and he calls you foolish.
- Euripides (484 BC - 406 BC)
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Thursday, September 04, 2008 6:34 PM
To: PSUBSorg
Subject: [PSUBS-MAILIST] Upward Buoyant Pressures on Ambient Interior
Surfaces
Upward
Buoyant Pressures on Ambient Interior Surfaces
Grand Greetings
SMMOM's ;)'
I've been pondering
this question for some time now, when I was designing a couple if different
ambient subs in my head. Doug, I believe brings up some good points
below about the higher PSI inside the ambient subs being a little higher. He
also made a point recently about the PSI being a little higher from the
constant flow of air, coming into the cabin for breathing.
I was thinking that
there is one more thing item we need to consider. That being that air is
really buoyant, as we all know. So one of the main reasons that 1 ATM
subs are so heavy, is that they need to counter act the buoyant forces that the
air in the interior is exerting upwards. So that means to me that all the
air in the ambient subs cabin is mostly pushing upward on any surface that's
there. This is why I was thinking that a hatch and/or any windows and
frame work can handle that amount of buoyant pressure that is trying to lift
the sub, and will do so, if you release a drop weight. For some large ambient
cabin spaces, I would think that pressure might be substantial. Any
thought? I wouldn't be surprised if I missed some thing.
Your resident bubble dweller ;)'
Regards,
Szybowski
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] depth indicator
Date: Fri, 29 Aug 2008 09:55:57 -0400
From: djackson99@aol.com
I
think the correct answer is "almost" no difference.
Take a
4 ft pipe.
Cap one end and anchor the
open end to the bottom of a lake so that the cap is just below the surface.
Now fill the pipe completely with air. At the open end of the pipe the air
pressure is equal to the water pressure and a depth indicator will read the
same if it is inside or outside the pipe. But at the top of the pipe the
water pressure outside the pipe is zero and the air pressure inside the pipe
still indicates the pressure for 4ft of water.
So my dive computer outside the view port will indicate the depth of the view
port, and inside it would indicate an additional 3+ feet, to were I release air
into the surrounding water.
Best
of Luck
Doug
www.submarineboat.com
-----Original Message-----
From: Jay K. Jeffries <bottomgun@mindspring.com>
To: personal_submersibles@psubs.org
Sent: Fri, 29 Aug 2008 5:01 am
Subject: RE: [PSUBS-MAILIST] depth indicator
In ambient sub senses the same pressure inside or out so there
is no difference having the gage inside or out.
Talk sense to a fool and he calls you foolish.
- Euripides (484 BC - 406 BC)
Hmmmm...
Not the weight of the sub. It should indicate the depth of the vent where the air is released
into the surrounding water and likely a little deeper since the constant flow
of air may add a few psi to the ambient cabin. Air at the top of the
cabin is at the same pressure as the air at the bottom of the cabin where it is
vented to the surrounding water. So it does not matter where the gauge is
inside the cabin.
That also makes the air at the top of the cabin at a pressure higher than the
water surrounding the top of the cabin. So a hatch in the top of an ambient sub
seals naturally if it opens inward. Completely opposite to a 1ATM sub.
In my case the dive computer is going to ride along outside the forward view
port. There is no room for it inside and with it outside it will automatically
start logging the dive when it submerges.
So what are you thinking of building?
Doug J
www.submarineboat.com
In an ambient submarine, if one uses a dive watch type depth indicators to give
an indication of how deep He is, does this display the actual depth or will it
be off a little having the additional weight of the sub working on it? One of
those HMMMM thoughts...
David Bartsch
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