RE: [PSUBS-MAILIST] depth indicator

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.

In ambient sub senses the same pressure inside or out so there is no difference having the gage inside or out.

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 djackson99@aol.com
Sent: Friday, August 29, 2008 1:08 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] depth indicator

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

-----Original Message-----
From: David Bartsch <dbartsch2236@hotmail.com>
To: personal_submersibles@psubs.org
Sent: Thu, 28 Aug 2008 11:11 pm
Subject: [PSUBS-MAILIST] depth indicator

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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