stunaep:
my test on my new 13 cu. ft. pony tank
starting with 3000 PSI / (avg of 161 PSI/minute)
one atmosphere -- 0 ft; 18.6 minutes
two atmospheres -- 33 ft; 9.3 minutes
three atmospheres -- 66 ft; 6.2 minutes
four atmospheres -- 99 ft; 4.6 minutes
feedback, please...
--carlos
It looks like you are using a SAC of 0.75 or so. So, let's start the scenario at 100 feet, and assume your SAC is at that rate, although if you've had a problem it seems to me a higher SAC of 1.0 would be appropriate.
100 feet, problem, switch to pony, breath on pony for 1.15 minutes. a quarter, or 3.25 cubic feet are gone, more likely closer to 5 if you are stressed.
Ascend to 70 feet at 30 fpm (remember, let's try not to get bent here). 1 minute, average depth of about 85 feet, so, call it 2.5 more cubic feet at a SAC of .75, more like 3+ if you are stressed.
Ascend to 40 feet, 30 fpm, use 2 cubic feet. At this point you are more than half way through your bottle if your SAC is 0.75 and probably down to about 3 cubic feet if stressed. You are really only a minute from the surface, so you may have gas, but not enough for a safety stop . . . and remember, let's not get bent.
Throw a wrench into the equation. It is your buddy that runs out of air at depth. You hand him the pony, it takes two minutes to square things away at depth. He's a hoover, and he's stressed. POOF, 8 cubic feet gone before you start up . . . minimum 3 minutes at a reasonable ascent rate with no safety stop, he doesn't have the air to do the ascent, much less the stop.
I dunno, seems to me like a 13 cubic foot pony bottle is no good for an ascent from 100 feet, I am, of course, assuming you are contemplating that because your numbers go down that low, and I recognize that assumption. That being said, it is something to think about.
