Alright, let's face it. Making an underwater house wont be easy. The very first trial I intended to do will be a single room building
in the lake behind our house.
Concept:
The room will be a box with Plexiglas windows in it so that you can look out and the underwater habitat. The room's depth will be no
more than 10 feet under. The actual dimensions will probably be 6' x 6' x 4' tall. Part of the "floor" will be left open to the water
beneath and will serve as the entry way into the room.
First, let's consider the sort of environmental challenges we will be facing. Probably first and foremost in everyone's mind is
pressure. Lot's of pressure. To be a little more precise, pressure will increase about .455 psi per foot of depth. That's dependent
on the density of the lake water though. The actual equation is nothing more than f=ma with a slight twist. On top of that you need
to tack on 14.7 atmospheric psi. Our 10 foot depth will be approximately 19 psi. This wont really be a problem except for the
Plexiglas windows. Plexiglas can only take 7,000 psi. This allows for a maximum window size of a 19 inch square window.* For
safety, I'll end up going with an 18 x 18 inch window, which will only suffer a maximum of 6,156 psi. This is a bit smaller than what
I initially wanted (HUGE windows stretching 5 feet across), but 18 inches isn't exactly minuscule either.
The next thing most people worry about is air supply. The human body (when in a relaxed state) uses about 1/4 of a cubic foot of air
per minute. The normal 20% oxygen in the air is depleted to 15% after the lungs are done with it. From this bit of information we
can realize that the lungs use up 25% of the oxygen with each breath. This mean that our 144 cubic foot room will hold enough air to
last 9.6 hours and still be clean. If you were to wait until the oxygen dropped to 10% the time would be 23 hours worth of air.
Obviously, it would be unwise to stay under that long, but humans CAN function at those lower level oxygen levels.
Replacing the air will be a harder trick. I have not yet decided on the best way to go about this. One idea is to flood the entire
room, and then refill it with surface air. Sadly this would mean that you could not keep any objects that need to stay dry in the
room. Another idea is to flood up to the base of the main area and then refill it again. Since CO2 produced by the lungs is heavier
than oxygen, this could work. You might even be able to hook up a toilet mechanism that controls the inside water level. This would
require compressed air though. Again, I have not yet decided upon which course to take. My mind is still open to new and exciting
ideas.
Something most people do NOT think about is the lift such a room would exert. Essentially you are trying to hold a giant air bubble
underwater. Not an easy task. I experimented around with some coke cans and chanced upon Pascal's law through my efforts. It's
going to take an equal weight of ballast to hold down the weight that the water would have occupied. Water weighs 62.4 pounds a cubic
foot. That's a lot. In fact, that's almost 9,000 pounds of lift I need to hold down (144 * 62.4). With 5 trashcans filled with
concrete that is probably possible. It all depends on how many cubic feet of trashcan I can find.
Of course there is always the problem of decay of materials. Things tend to decay underwater. Wood in particular. I've decided that
probably roofing tar will hold off all the water, though I do not know this for sure. Possibly the way to go is use whatever is used
with swimming pools.
In summary, I'm very tired and it's past my bedtime. Please let me know any suggestions you might have.
* This calculation is actually wrong. I could have had my much larger windows, because I had forgotten to subtract the
room pressure (i.e. assumed inside vacuum). If you keep the inside pressure at atmospheric pressure the windows can be quite
large. A size of 3'x 3' would have been conservative.