Ambient-Dry (was:Pressure regulation)

[David Buchner <Buchner@wcta.net>]

Stan (<SFreihof@aol.com>) said:
>The design I have chosen is ambient pressure dry, which is pretty simple
>because it's not much more complicated than inverting a glass and submerging
>it.  The air can't get out, so the water won't come in.

Do you have, or do you know a clever way to figure, how much the water
level inside will rise as that 'glass' submerges? I mean, the air pressure
is rising to match the outside (water) pressure because the air is getting
squished into a smaller area and the cabin is being invaded by water from
underneath. I'm wondering how much extra space you're leaving down there so
your feet don't start getting wet as you go deeper. Or will it not even
rise that much, so that it isn't a concern? Or do you keep adding air to
maintain the same volume while maintaining the same pressure? Or... what?

>The drawback to ambient pressure subs is that you are under pressure with
>depth, so the normal limits of scuba diving apply regarding depth and time.
>The deeper you go the less time you can stay without requiring decompression.

What sorts of depths and times are those? I'm not asking so I can fake my
way around study or training, scuba certification, etc. -- but so's I'll
know what range that is so I can make sure I'm avoiding it altogether.

>The design I am working on has two hatches (redundancy is good)!  One is on
>top for entry and egress on the surface, and one on the bottom for
>entry/egress when parked on the bottom

I have thought about doing this myself. So, will the whole thing sink like
a stone (or more like a heavy metal thing with holes in the top and bottom)
if both hatches are stupidly opened while submerged? Or are you planning
for so much other flotation stuff that the cabin air isn't what's keeping
you from sinking in the first place? I mean, the way I've thought about it,
you have to make the whole thing heavy enough to submerge the air volume
inside, right? Then add ballast tanks which keep that whole mass floating
when they're full of air, and let it sink when the air is let out. So if
you let the air out of the cabin too, there'd be no way to get it back up.
Right?

>I have opted not to use a scrubber because of cost and inherent dangers.  Most
>CO-2 absorbants create toxins when wet (correct me if I'm wrong)

I was also wondering where you get properly get rid of the stuff once
you've used it -- or whether it's something which can be baked or squeezed
or otherwise processed to make it re-usable.

******
>First, let me say that I think an acrylic sub would be REALLY unique!
>Maybe I misunderstood your design intentions, but I assumed you were
>attempting to build a 1 atm (pressure hull) sub.  Using acrylic as a
>structural material though, I would worry about trying to make it a 1
>atmosphere (or pressure hull) submarine.  So I suppose you are considering
>either an ambient pressure design (either semi-dry or dry), or a wet design.

Actually, another of the ancient Popular Science sub features (I can dig it
out and scan it in the spring if you don't believe me) was a transparent
(glass, I think) sphere with no openings at all. It was two halves bolted
together with the occupant(s) inside (yikes!), suspended in an independent
drive section and the controls communicated to the stuff they were
controlling, through the glass, by radio or infrared or something. I don't
know whether it was ever built or not.