13 cubic foot bottle

[DandyDon]

The way I selected my pony between the 13 & 19 was based on...

The 19 cf weighed 7.8# with valve, only 2# heavier than the 13;

The 19 cf cost $10 more than the 13 but used same everything else;

The 19 had 50% more air, whether I needed it or not.​

So I don't know why anyone would want a 13, except maybe that it's shorter...?

 

[Wookie]

So I don't know why anyone would want a 13, except maybe that it's shorter...?

Ding Ding Ding
We have a winner! When my tank is in the tank rack, the 13 stays attached. I'd have to remove the 19, or rig it so the valve is much higher than the valve on my 100.

 

[DandyDon]

Ding Ding Ding
We have a winner! When my tank is in the tank rack, the 13 stays attached. I'd have to remove the 19, or rig it so the valve is much higher than the valve on my 100.

Thanks; I have wondered. If I was an expert diver like you, I might consider the shorter 13 - except I sling mine in front, and originally got it because of the of the boat pic buddies I dived with.

 

[Wookie]

Thanks; I have wondered. If I was an expert diver like you, I might consider the shorter 13 - except I sling mine in front, and originally got it because of the of the boat pic buddies I dived with.

WHen I sling a short cylinder like a 13 or a 19, or a 30, i tend to carry it out in front of me. I don't like it when the cylinder hits me right in the Mummy/Daddy button.

 

[Captain12Pk]

"I'd also factor in the idea that if you're at 130ft and have just had the unpleasant surprise of taking the LAST available breath off the single tank on your back - and your buddy is no-where in sight - you're SAC is gonna go up just a tad."


I would agree 100%... and I considered mentioning that, but since that wasn't the scenario mentioned in the OP... well. I would bet that if the pony were employed in an actual OOG scenario, the sac would probably be a min. of 1.0. Maybe as high as 1.5.
I also considered mentioning that I have a great Luxfer al 27 in the garage I'd sell cheap.

 

[Doc Harry]

Would there be enough air in a thirteen cubic foot bottle to make an ascent from 130 feet, which would include a one minute stop at 30 and 50 feet and a three minute at 20, for a person like myself who is pretty easy on air most of the time?

Assume SAC = 1.0 if you're bailing out
Assume 1 minute at 130 feet to work out problems
Assume ascent rate 30 feet/min with average depth halfway between
Assume 1 minute stop at 50 feet, as you stated
Assume 1 minute stop at 30 feet, as you stated
Assume 3 minute stop at 20 feet, as you stated

TOTAL REQUIRED GAS:
1 min x 130 feet (4.9 ATA) x 1.0 cu.ft./min = 4.9 cubic feet
1 min ascent x 115 feet (4.45 ATA) x 1.0 cu.ft./min = 4.5 cubic feet
1 min ascent x 85 feet (3.55 ATA) x 1.0 cu.ft./min = 3.6 cubic feet
1 min ascent x 60 feet (2.8 ATA) x 1.0 cu.ft./min = 2.8 cubic feet
1 min at 50 feet x 50 feet (2.5 ATA) x 1.0 cu.ft./min = 2.5 cubic feet
1 min ascent x 40 feet (2.2 ATA) x 1.0 cu.ft./min = 2.2 cubic feet
1 min at 30 feet x 30 feet (1.9 ATA) x 1.0 cu.ft./min = 1.9 cubic feet
1 min ascent x 15 feet (1.45 ATA) x 1.0 cu.ft./min = 1.5 cubic feet

TOTAL REQUIRED = 24 cubic feet to get you back on the boat with 0 p.s.i. remaining

 

[redacted]

If you practice with that redundant air source and have confidence in your skills to surface using it, why should your SAC increase just because of a LOA or OOA situation?

 

[Doc Harry]

If you practice with that redundant air source and have confidence in your skills to surface using it, why should your SAC increase just because of a LOA or OOA situation?

Because in real life, SAC always increases no matter how well-trained you are.

Because you should plan too have too much gas in a worse-case scenario, not the opposite. I'd rather get back about the boat with 300 p.s.i. remaining in my bailout bottle after completing all of required stops, than have to make a CESA from 50 feet because I incorectly assumed that I'd be calm, cool and collected in an emergency.

But, I posted all of the assumptions for the calculations. So you can change those assumptions and re-work the calculations to come up with your own figures.

 

[walke121]

Would any of us actually stick to 30ft/min ascent rate if we were OOA and breathing on a pony??? Just posing a question. I know I would have a hard time with that. I would get to 60ft. really quick then start a slower ascent.

 

[Doc Harry]

Would any of us actually stick to 30ft/min ascent rate if we were OOA and breathing on a pony??? Just posing a question. I know I would have a hard time with that. I would get to 60ft. really quick then start a slower ascent.

In reality, probably not.

I know from deco diving that I tend to ascend a lot slower than 30 feet/minute, and I have to always speed up my ascent to stay on schedule. It feels way too fast, 30 feet/minute.

Have you ever tried to ascend at 60 feet/minute? To me, ascending at 60 feet/min feels like I'm rocketing to the surface with reckless abandon.