Re: [PSUBS-MAILIST] Ambient / 1ATM Q?

Bill, Patrick, & Chip

Yes, a lot of ways to skin that cat. Mine is only one way and as I have chosen it, I neglected to mention the others. That's your job Patrick or anyone else, to gather information from various sources and independently verify the validility of that information. (The fork in your eye ethos).

I came up with a way to minimize that waste of air you mentioned Bill. I will use a 12v centrifucal blower at snorkel depth for air flow and save the tanks. I stole (ah...borrowed) the idea from two places. The 10 psi blower system on the fleet boats, and I believe the Aquasub pontoon semi-submersible uses a blower in the ventilation system on the port float. The 12v blower may be able to blow ballast as well, I don't know yet. I have to look into the blowers specs.

There was a discussion some months back regarding the use of LP air at the surface for blowing ballast. That discussion caused me to think about, how many things can I get the snorkel to do? So far,... cabin ventilation / compensation at snorkel depth, engine air induction / ventilation, and surfacing the boat.

I am (borrowing) Ricks use of the second stage regulators for use in the engine compartment only to feed the diesel a little air should the flapper valve close on the snorkel intermitenly from say, wave action or sloppy depth keeping. Otherwise, your eardrums become that membrane you mentioned Chip.

Someone said to me not long ago, why bother, that I would end up with a deep draft boat. Well, it's a facsimile of a military sub which is designed to simply appraoch it's target by stealth. Simply submerging does that. Besides, bouyancy and rate control in an ambient are a bit dicey at depth. This way keeps me out of trouble.

Joe

From: "Akins" <lakins1@tampabay.rr.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Ambient / 1ATM Q?
Date: Thu, 19 Jan 2006 14:26:37 -0500

For Patrick and Joe.

Joe is right Patrick. That is ONE way to do it. As Joe described, by having a constant flow of air going into the hull's interior from the air tanks and exhausting any

extra internal air pressure outside (by using an overpressure valve) if it is not needed to equalize against the outside water pressure. I assume this is how Rick and Joe are keeping their hull interiors almost completely dry.

I did not realize Rick and Joe were using constant air flow in their ambient designs. Now I see why their hull interiors are almost devoid of water vapour.

I say ALMOST, because there is still some condensation that can form inside the hull interior from the moisture in the air that was inside your hull before you closed the hatch. This forms

water droplets inside the hull due to temperature level drops, just as water forms on the outside of a cold glass of icewater. This can happen in a 1 atm sub too.

As Rick pointed out earlier this can be handled by dessicant absorbant which is a powder which absorbs water.and basically wicks water out of the air. The air in their tanks is much dryer than normal air also so this helps too.

However; this method uses a lot of air with it flowing constantly. This would be fine if you have a diesel running an air compressor to replenish your air tanks on the surface. Not so good if you are just running

electric and using finite air tanks. Suspose you are at the depth you want to be and are no longer descending. You just want to run horizontal. Now there is no increase in external water pressure. But in the system

Joe described your air is still constantly flowing and any extra not needed to equalize the hull is exhausted outside. You can see this wastes a lot of air that you are not using for breathing.

So there are a few different ways to equalize your ambient hull against outside water pressure by using internal air pressure Patrick. Some designs have the operator

completely dry and breathing from the air that was in the hull when the hatch closed, and then when it becomes stale he can breath from a scuba regulator.which exhausts his co2 outside the hull via

a tube and one way exhaust valve. Or he can just start off breathing from the scuba regulator and keep the cabin air in reserve. Some designs just have you breathing from the air in the hull without any provision for breathing

thru a regulator and when the cabin air becomes stale you have to surface. It's a good idea to take a spare air small bail out bottle with you for emergencies though.

What all ambients have in common whether they have an opening to the water (like in an upside down glass) and use the rising water level to trip a float, valve or sensor

which then activates their air tanks to vent, or whether they are closed to the water and use a valve or sensor, is that they use internal air pressure to push back against the external water pressure. Thus removing the need for a pressure hull at

shallow depths. The thing is Patrick, there is more than one way to skin a cat with ambient designs.

Bill Akins.

----- Original Message -----

From: Joseph Perkel

To: personal_submersibles@psubs.org

Sent: Thursday, January 19, 2006 11:40 AM

Subject: RE: [PSUBS-MAILIST] Ambient / 1ATM Q?

Patrick,

As the question is specific to an ambient dry sub which is my design profile, I will answer you in that regard. Whereas a semi-dry or open ambient has a direct connection to the outside ambient pressure, to remain a truly dry ambient requires the use of check valves.

The pressure is equalized by a constant flow of air introduced into the cabin which opens the check valves and dumps the overpressure outboard. The outside ambient pressure does not directly impact the cabin as you noted. There is a delay in compensation, which limits descent rate to design structural capability.

To oversimplify the 1 atm vessel keeps the pressure out by the brute force of it's designed structural integrity.

Joe

From: "Patrick" <pat_man_ta@hotmail.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: [PSUBS-MAILIST] Ambient / 1ATM Q?
Date: Thu, 19 Jan 2006 11:21:48 -0500

I am having some trouble wrapping my head around HOW the outside pressure influences the inside pressure in an ambient dry sub and how a 1ATM sub keeps the pressure out. Could someone explain this to me?

-patrick

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