I'm open water certified, so here goes.
A submarine that maintains 1 atm inside simply has to be made strong enough to resist being crushed by the water pressure outside it. if you plan on
going down 10 meters, you'll need it to resist 14 pounds per square inch of inward pressure. This is pretty much linear all the way down, with every
10 meters or so adding on another 15 pounds per square inch of pressure.
Pure oxygen is toxic at high pressures. Don't even think about using it beyond about 30 feet down. Pressurized air is better, but the nitrogen in it
will become dissolved in your blood over time, so deep and or extended dives will require decompression stops. Helium and oxygen mixes are better,
because helium comes out of solution in blood faster, doesn't dissolve in tissue as fast, and has far less of a narcotic effect than high pressure
nitrogen. Trimix is a common blend used for technical diving, and it's got oxygen, helium, and nitrogen.
Here's the dive table I use to determine dive duration, and how long to stay above the surface before diving again.
External source: PADI Dive table
In a spaceship, or, to a lesser degree, the hull is there to keep the air inside from bursting it and escaping, and is pushed on only by the air
inside. In a submarine, the hull is there to keep the pressure of the water from crushing it and entering. it is pushed on from the outside. In both
cases, the best shapes are spheres and cigar shapes. Submarines tend to take this more literally than aircraft and spacecraft, because spacecraft at
most have 1 atm to hold in, while deep sea submersibles may need to hold out a dozen atm of pressure. Usually, a spacecraft will only be pressurized
to 5 psi of pure oxygen, making it require a hull only as strong as a submarine intended to dive to 10 feet down.
Originally posted by defcon5
reply to post by Phage
What you are saying makes sense, yet there must be something more to it yet. My tank is also rigid (I have used steel and aluminum tanks), yet my air
decreases with each BAR that I descend. There is actually a chart that they use in diving, which shows that 33 feet = 2Bar = 2x density = ½ volume,
66 feet = 3BAR = 3x Density = 1/3 volume, etc.
Unless that all simply happens between the first stage regulator and my lungs, I don’t understand why it would happen at all. Besides this I have
actually gone down to 100 feet, and watched the PSI in my tank drop on my guages coming right from the high pressure port on my first stage regulator
(which bypasses all the other hoses and such), then increase again on ascent.
So for example: I have 3000PSI at the surface, at 99 feet I have around 1000PSI (of course that is off some cause I would have breathed some of it).
Then if I return right back to the surface I would be back up near 1500-2000 PSI (of course it would be lower because I consumed more when the air was
denser).
See what I mean?
You're wrong. That doesn't happen. I've never seen anything like what you're talking about. You get less use out of your tank because further you
go down, the more air is in each breath you take. The air, if you weren't breathing from it, would remain at a constant pressure through the whole
trip. Your consumption of the air increases greatly at depth; you use it up twice as fast at 30 feet as you do at the surface, three times as fast at
60.
once the air is outside the tank, it's at the same pressure as the water around it. If it were any less, it would be instantly crushed down until it
was. The regulator lets out gas at ambient pressure.
If you were in a sub at 1 atm, you'd use it at the same rate as you would on the surface.
I have to wonder if, at depth, could you hold your breath for much longer, due to the increased oxygen content in each breath? or would the buildup of
CO2 cause a need to exhale? I never tried because I'm trained to always maintain a steady breathing rate to prevent lung overexpansion.
Didn't your instructor cover all this during training? we spent a few days on the science of it all.
Anyway, I'd suggest a diving bell type contraption over a real pressure controlled submarine, if you plan on building it. It would be so much easier.
