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Re: [PSUBS-MAILIST] Unlimited air supply?

Hi Dino and group.
 
Let me rephrase one of my below statements. In my below statements I stated 33 ft as being 1 atm. That is not correct actually.
Sometimes divers will say "I only went to 1 atm to 33 ft depth" This is a common mistake we all make. What we mean is we actually
went to a 1 atm depth  OVER what is normally 1 atm at the surface which is 14.7 lbs psi at the surface. So if you go to a depth of 33 ft,
you are actually at 2 atm, not 1atm. I hope this did not create any confusion in anyone's mind. Sometime as divers we make semantic
mistakes because we are so used to other divers knowing what we mean that we forget to add in the 1 atm from the surface to our total
when we are discussing depth.
Bill Akins.
 
 
 
 
----- Original Message -----
From: Akins
Sent: Friday, February 10, 2006 6:53 PM
Subject: Re: [PSUBS-MAILIST] Unlimited air supply?

Hi Dino.
 
You wrote.....
 
"Has anybody built a sub with 1ATM air normally, but the option to use 2+ATMs
for the occasional deeper wreck dive? Of course, nitrogen bubbles would have
to be dealt with as per scuba diving."
 
 
 
Some months ago I proposed a similiar idea here to the group. My idea had you building a 1 atm sub that's interior could be further pressurized
so it could go deeper than it normally could. I think my idea came from some of the other members discussing building a 1 atm sub out of
propane tanks. Some of the expert members here expressed their beliefs that using a propane tank as a 1 atm sub is not safe for a variety
of reasons and they believed a regular pressure hull should be created instead. Some other members who have propane tank subs already
disagreed with them and believe their hulls are safe as long as they do not exceed a certain shallow depth. 
 
This discussion caused me to think about a propane tank that would only normally be used to a relatively shallow depth, being able to go an
atmosphere or two deeper by pressurizing the interior of the propane tank to make its hull able to take the stress of going deeper than it normally could.
Say for instance you have a propane tank sub that you have only tested to 1 atm (33 ft) and everything was fine at that depth but you are afraid to go any
deeper because you do not think the hull will take any more pressure. If you further compressed the interior atmosphere in the propane tank to say 2 or even
3 atm, your hull would be able to go twice to three times deeper than you normally would go in your propane tank sub. In other words you are using your
propane tank sub as a 1 atm sub down to 1 atm, then just like an ambient sub, you pressurized the interior to 2 atm and you can now go twice as deep with
the same stresses on your hull because your interior pressure is pushing outward against the outside water pressure just like an ambient sub does. This would
make your sub a hybrid of 1 atm and ambient operation. Although the Hunley did not operate exactly like this, I got the idea from some similiarities she had to
this idea. The old girl is still teaching!  I thought to myself....Why do this? Well........one reason would be.....suspose you normally just want to operate your sub at 1 atm where you live.
You ordinarily do not care to go much deeper than 1 atm in your propane tank sub. You could operate it as a normal 1 atm sub at 1 atm depth without any worries about having to
adhere to dive tables. So you would have an advantage over an ambient sub that WOULD have to adhere to dive tables at 33 ft depth (1 atm). 
Now suspose there are occasional times that you would like to go an atmosphere or two deeper. Having the ambient capability to further pressurize your
normally 1 atm interior would allow you to go much deeper.Then of course you would have to adhere to dive tables. This would give you the option of having a 1 atm sub for shallow
depths and then being able to convert it to ambient for diving deeper if you wanted to. A hybrid of the 1 atm and ambient systems. I do not know if anyone has home built anything like this.
 
Bill Akins.