Pony Bottle / Spare Air

[JohnB47]

Safety stops are considered optional--that's what distinguishes them from deco stops. If I were calculating my minimum gas needs in an out-of-gas situation, I would not factor in any deep stops, 1 minute stops every 10 feet, or a 3 minute stop at 15 feet. I would assume an ascent at 60 feet per minute to 60 feet, and 30 feet per minute to the surface.

It's up to you what assumptions you want to make. I assumed that in an emergency, I would use the whole tank rather than holding back 500 psi, but I decided that I would like the option to do a safety stop. You have to make some kind of assumptions in order to make calculations, and the point is that once you decide on what assumptions you are comfortable with, you can calculate the maximum depth from which you can make a safe ascent with a given size pony tank. When you do so, it becomes very obvious that 1.7 or 3.0 cu. ft. is not very much air, but that 13 cu. ft. is probably adequate for a bailout from normal recreational diving depths. If you dive deeper than that, maybe you should consider 19 cu. ft. or more. I would encourage anyone who is thinking of buying a redundant air supply to make the calculations rather than just buying whatever is currently popular.

 

[GrumpyOldGuy]

John,

After 200 dives, why would you not use your historical SAC rather than an unsubstantiated number from the internet?

 

[JohnB47]

I have not measured mine in many years. I really need to re-measure it one of these days. My lowest measured value, based on a 2 hour dive to 10 feet in warm water in the Little Miami River in Ohio, was about 0.45 cfm. I am sure that it is considerably higher now, as I am older and fatter now. Anyway, I used an "average" value because it would be more conservative, and because in an emergency situation, one's air consumption could be expected to increase due to stress.

 

[surfacewatch]

Hi,

In my experience the best thing you can do to avoid getting into trouble is keep an eye on your gauges and dive with a reliable buddy, if you're going deep set a stage bottle from the boat as a backup. That way you don't have to carry around any extra equipment thats just going to weigh you down and get in the way.

If you're considering cave/wreck penetration might make you feel safer with spare air but there's not much air in there and you don't want to give yourself a false safety net. Pony bottles are good for long dives/penetrations if you know how to use them and tie them on properly -again I would consider laying up stage bottles to save carrying so much around.

If you plan your dives properly and check your gauges you should never run out of air! I guess that's my old-school opinion!

all the best,
deborah
surfacewatch.com

 

[Aaron528]

Hi,

In my experience the best thing you can do to avoid getting into trouble is keep an eye on your gauges and dive with a reliable buddy, if you're going deep set a stage bottle from the boat as a backup. That way you don't have to carry around any extra equipment thats just going to weigh you down and get in the way.

If you're considering cave/wreck penetration might make you feel safer with spare air but there's not much air in there and you don't want to give yourself a false safety net. Pony bottles are good for long dives/penetrations if you know how to use them and tie them on properly -again I would consider laying up stage bottles to save carrying so much around.

If you plan your dives properly and check your gauges you should never run out of air! I guess that's my old-school opinion!

all the best,
deborah
surfacewatch.com

FWIW, the last dive trip I went on in the Bahamas, I was alone and not with my wife, who is my "reliable" buddy. The person who agreed to be my buddy on the dive boat submerged before I got in the water, then took off on his own in the opposite direction. At that point, I had a choice to abort my dive and waste all that money, or continue alone. I continued alone. IF I had an equipment problem (sticking gauge maybe?) and I didn't have a pony, I would have possibly been looking at a CESA from 50', with nobody else around.

I agree there are a few "what ifs" in my scenario that don't happen often. I service my gear regularly and I haven't had my own gauge stick, but it did happen to me with rental gear. Bottom line, S@@t happens and it doesn't matter how much pontificating someone does from the comfort of their computer. I will continue to dive with a pony because it makes me feel more comfortable to have it than not, and it's for the unexpected, not what happens within the parameters of a "reliable buddy and often checked gauge."

 

[Dr Wu]

Hi,

if you're going deep set a stage bottle from the boat as a backup. That way you don't have to carry around any extra equipment thats just going to weigh you down and get in the way.

Any tank you don't take with you is not going to do you much good in the event of an emergency at depth.