Pony bottle question

[Locus]

You need to determine how fast your use air, if you want any buffer to handle problems on the bottom and if you want to have air for a safety stop. Tonight I was packing for a 90 ft dive tomorrow. I have a choice of 13 or 6 cu-ft tanks and I grabbed the small one because it is so small and I will not be in deco.

Personally I wouldn't bother investing in tanks that small, since the depths for which they would be useful emergency supplies would be so limited IMO. Using Lewis' figures from the article I cited, a 6cu ft tank has slightly more than enough capacity for a 5-minute safety stop at 15', and that's it. To my mind, we bordering on false-sense-of-security territory. On the other hand, you have a great deal more experience than I do, so YMMV.

The AL40 is ample for my max depth, and if I want redundancy on shallower dives it is extra-ample, plus carrying it keeps us in practice for deeper, more challenging dives. This makes it a blanket solution as I see it (short of proper doubles, of course). I have long since abandoned any aversion to lugging bulky gear around. The more you do it, the better you get.

To me it comes down to this: If I'm at 40m and I have a serious problem, I want to be sure that I have enough gas to ascend at an appropriate rate and do a full 5-minute stop, plus extra air in case something else goes wrong along the way. Beware the cascade...

Coming up hastily from max depth while my mind races to choose which corners I'm willing to cut on ascent is not an experience I ever want to have.

I'd love to know how you get that AL40 onto an airplane when you travel. . .

It's never been an issue; I haven't done a dive trip yet that involved more than a car ride and a ferry : )

 

[Basking Ridge Diver]

So... the real discussion point is - where is most of your diving? From boats or from shore?

I dive a lot from shore - the pony bottles do get heavy when you are lugging them from place to place. So the thought is to balance the weight with the actual need with your RMV and your personal risk factor. I dive a 19cu ft pony because it is light enough to go on every dive with me. No excuses I take it with me unless I am less than 30 feet - I can make it to the surface from that point.

There was someone that claimed he takes an 80 cu ft and a 40 cu ft for reserve on his solo dives because his risk level is very low. I am not sure how that person handles the weight of those tanks and as he claimed diving with doubles. Personally I think it was a story - he claimed it was for real.

So you need to balance your risk with carrying a lighter pony that you will take with you every time you dive or carry 120 cu feet of air for every emergency you can think of so you survive. No one can answer that question for you - only you can. But please - if you dont know the formulas just ask or do some research and if you dont track your RMV - start tracking and know what you are getting into from a pony size. Whatever you chose will be better than nothing but at least - you will know why you chose to lug that boat anchor around when you decide it is too heavy...

 

[Nemrod]

I cannot justify a pony bottle half the size of my back gas. A more typical size would be 20% to 30% of back gas. An 80 cf back tank a 19 and certaily no more than 30 cf is appropriate IMO. An aluminum 80 is 77cf so that is around 23 cf using the Rule of Thirds therefore a 19 is reasonable for moderate deprhs and a 30 for deep.

N

 

[redacted]

There is at least one live-a-board that will allow an AL30 pony but not an Al40.

I don't understand why divers think they will "panic" and double their SAC in a LOA situation where they have a fully adequate redundant gas source. I find an Al13 is adequate in most cases but requires a bit more gas management than an Al19.

 

[halocline]

Think of it this way, a 19cft pony is somewhat equal to 750PSI in an AL80. If you are comfortable with a 750 PSI reserve, which for most recreational divers is plenty, then a 19cft pony should also be plenty.

Some divers often will argue that more gas is always better, but I don't think it's that simple. If you are recreational diving and you believe that you really need an additional half a tank for 'safety' then I suspect you're not really doing safe recreational dives. Solo diving at 100ft+ is NOT recreational diving as defined by the major training agencies. Pushing NDL because you have the extra gas is likewise not a safe practice. Once you start carrying a significant amount of extra gas, your dive behavior is inching into the technical diving realm, and to me that means more and better training, not just carrying extra gas.

It's a little analogous to hiking in mountains where you want to carry a rope and/or ice axe because you might encounter conditions or weather that would necessitate such gear. Usually, that's technical mountain climbing, not hiking.

In both activities the line between 'recreational' and 'technical' is not clearly defined, and safe practices rely more on judgement and the avoidance of risky behavior (and conditions) than choice of gear.

 

[Dave616]

Between my wife and I, we have a 19 and a 30, which covers just about everything in rec limits.

Edit: Buy them in brushed (natural) or black finish if possible. The bright yellow is annoying...

 

[dumpsterDiver]

So... the real discussion point is - where is most of your diving? From boats or from shore?

I dive a lot from shore - the pony bottles do get heavy when you are lugging them from place to place. So the thought is to balance the weight with the actual need with your RMV and your personal risk factor. I dive a 19cu ft pony because it is light enough to go on every dive with me. No excuses I take it with me unless I am less than 30 feet - I can make it to the surface from that point.

There was someone that claimed he takes an 80 cu ft and a 40 cu ft for reserve on his solo dives because his risk level is very low. I am not sure how that person handles the weight of those tanks and as he claimed diving with doubles. Personally I think it was a story - he claimed it was for real.

So you need to balance your risk with carrying a lighter pony that you will take with you every time you dive or carry 120 cu feet of air for every emergency you can think of so you survive. No one can answer that question for you - only you can. But please - if you dont know the formulas just ask or do some research and if you dont track your RMV - start tracking and know what you are getting into from a pony size. Whatever you chose will be better than nothing but at least - you will know why you chose to lug that boat anchor around when you decide it is too heavy...

The pony is for redundancy. A giant steel tank provides no redundancy AND my actually make things worse due to more nitrogen loads

 

[Basking Ridge Diver]

The pony is for redundancy. A giant steel tank provides no redundancy AND my actually make things worse due to more nitrogen loads

I am a convert - I carry a 19AL... the 120 I was talking about was an 80AL and a 40AL that he was carrying for redundancy... Sheesh...

 

[whitefang21]

i practical preferred the 40 bcs of the gas plan i have more than enough to get myself back to the surface making all the stops not doing deco. my favorite part IMO, the 40cuft has a better resale value.

An additional thought i have an extra inflator on my pony.*

 

[doctormike]

Gotta say, this discussion always confuses me. I carry an aluminum 40 now as a deco bottle, but used to carry one as a pony bottle when I was diving single tank. I never noticed that it was there, it just "disappears", even when using a large DSLR...

So given the choice between 13, 19, 30 and 40, I would take the 40. More gas is better, especially if you have a leak or free flow from the pony that you are counting on. I don't see much of a tradeoff in extra weight and size at all - in the water, a 40 and a 13 are about the same in terms of buoyancy. If anything, the length of the 40 fits a lot better when slinging than a small pony (compared to smaller tanks that I tried).

I guess if you are using a tank mount, a small bottle might be better, but that's another discussion!