Re: [PSUBS-MAILIST] Dif. Between Ambient & 1ATM

Sean wrote:

"When space is at a premium, and you can't use a dry chamber that a diver can exit the water to, you can use a wet trunk just large enough to accommodate the diver and permit him to close the hatch, but when blowing or pumping the trunk dry, you need to do this at constant pressure (i.e. by venting at ambient pressure), and then reduce the trunk pressure slowly enough that the ascent rate is reasonable"

I have been thinking about this problem for my (ambient)design and came up with the "wet trunk" idea as well but, ruled it out because of the buoyancy problems you mention and access.

I found that to egress, you would have to be bottomed, well "negatively" flooded and stable to accommodate the loss of the occupant'(s).

Where to put access was problematic for me as well so I ruled it out. But I have to tell you, Sportsub has this problem licked nicely with their particular ambient design. http://www.ivccorp.com/

Joe

From: "Akins" <lakins1@tampabay.rr.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] Dif. Between Ambient & 1ATM
Date: Wed, 15 Feb 2006 04:39:51 -0500

Hi Sean.

You wrote..."With ambient subs, getting a diver in an out doesn't require a hatch -
just leave a hole in the floor. Although, I can't imagine why you'd
bother trying to accomodate divers with an ambient design."

One reason for accomodating divers and having a hole in the floor with an ambient design would be if you saw

something down there that you wanted to pick up and bring into the sub. A second reason would be to further

explore something interesting that you see, but that you cannot get close enough to by virtue of being inside the sub.

A third reason would be for normal entry and exit doing away totally with needing any kind of a standard type hatch. A

fourth reason would be to do away with the need for a scuttle valve. A fifth reason that goes along with the fourth,

would be for an easy bail out in case of an emergency. A sixth reason would be in case a diver was injured or ran out of

air or had a 1st stage regulator malfunction and he had been compressed too long so that he could not immediately accend

without certain decompression sickness and possible death. He could come back inside the sub, breath the air in the sub,

hopefully attend somewhat as best as possible to any injuries until the sub could surface and seek proper medical attention,

and do all this as the sub slowly accended to avoid decompression sickness.

"imagine". Smile. Bill Akins.

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

From: Sean T. Stevenson

To: personal_submersibles@psubs.org

Sent: Wednesday, February 15, 2006 12:25 AM

Subject: Re: [PSUBS-MAILIST] Dif. Between Ambient & 1ATM

Ambient implies that the pressure within the hull is the same as the
pressure outside the hull at all times. Essentially, an ambient sub is
just like going for a SCUBA dive, only dry. The hull in this case does
not need to withstand pressure differentials in any direction, which
makes for much simplified construction, but then you are subject to
decompression requirements just as when diving.

A 1ATM sub maintains normal surface pressure within the hull at all
times, eliminating the need for decompression regardless of dive
duration. This means that the hull needs to be built to withstand the
external pressure at the design depth. The interior pressure will never
be higher than the exterior pressure in this case.

Diver lockouts incorporate a separate chamber within the pressure hull
which can be internally pressurized to match the external (ambient)
pressure. In this case, when pressurized the only part of the chamber
that has a pressure differential across it will be the bulkhead which
separates the lockout from the rest of the sub interior. Diver enters
the lockout, interior hatch is closed, chamber pressure is increased to
match ambient, exterior hatch is opened, and diver exits into the
water. The advantage of reasonable size lockouts like this is that they
can also be used as decompression / recompression chambers, maintaining
the returned divers at pressure even if the sub subsequently surfaces.

When space is at a premium, and you can't use a dry chamber that a diver
can exit the water to, you can use a wet trunk just large enough to
accomodate the diver and permit him to close the hatch, but when blowing
or pumping the trunk dry, you need to do this at constant pressure (i.e.
by venting at ambient pressure), and then reduce the trunk pressure
slowly enough that the ascent rate is reasonable - just like when
diving. This is more difficult to accomplish with a small volume. Same
idea though - once dry and returned to 1ATM, open interior hatch.

With ambient subs, getting a diver in an out doesn't require a hatch -
just leave a hole in the floor. Although, I can't imagine why you'd
bother trying to accomodate divers with an ambient design.

-Sean

C & L Hendkids wrote:

> Guys,
> From my understanding, the differance between ambient hull designs and
> 1ATM is that ambient is non-pressurized (resisting the pressure by
> structural strength) and that 1ATM is pressurized (resisting the
> pressure by structural strength *&* by internal air pressure, kinda
> like a 2L bottle of pop before you take the lid off. :o) ).
>
> Also, I was wondering if it would be feasible to have a submarine wet
> for diver entry and 1ATM after they are in. (It would be underwater,
> and the diver would open the hatch, get in, close the hatch, and then
> blow all the H2O out of the cockpit).
>
> Am I confused, or what?
>
> Just wanting a little clarification,
> Alan Hendrickson, Oregon, USA

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