I don't mean this to sound insensitive, but if you were in a submarine or similar vehicle, and

[raccoon]

banging or tapping to try to let someone know where you are, would it be better to bang every so often--every 15 minutes or whatever, or to bang something like "shave and a haircut, two bits"?

[Walleye]

1. I would probably go with a basic SOS

[Effete Snob]

5. Ah, much better

[brewens]

2. Chicken in the bread pan pickin' out dough. :) n/t

[allegorical oracle]

3. Heard last eve that the banging was occurring at 30 minute intervals. So a pattern was

ostensibly established. But I wondered why so many minutes apart? Then someone who was being interviewed pointed out that the occupants need to save oxygen and wouldn't want to exert themselves too often. A submersibles expert from Fla was on NPR and wasn't optimistic. He questioned that the craft's hull is carbon fiber and titanium, not steel. He added that it was not a device that he would've ever taken to 12,000 feet, where pressure is 6,000 pounds per square inch.

[Effete Snob]

4. Shave and a haircut

If there is the possibility of other mechanical noises in the area from engines other machinery and whatnot, then something other than a regular beat might more likely be understood as non-mechanical.

[ret5hd]

6. The Fibonacci Sequence...

1, 1, 2, 3, 5, 8...

to demonstrate that I was at the very least someone of the intellectual capacity to be worth saving.

[brooklynite]

7. Answer: more exertion equals more oxygen depletion.

[2naSalit]

8. One expert...

Can't recall which one, said that banging should sound human made. Easier to decipher so any recognizable pattern would probably work.