Pony bottle question

[Basking Ridge Diver]

I think the answer varies based on the types of diving you are doing and will do in the foreseeable future.

I night dive in inlets - shore dive off beaches and walk quite a ways to get to the water. I like to make it in one trip - I get geared up at my truck and take a walk - sometimes over jetties and slippery areas and sometimes walk in the loose sand for long stretches.

If you dive off a boat or go to a quarry - chances are you can drive your vehicle up close to the point you unload. Sometimes maybe you need to park your car away from where you just unloaded.

Each of these types of diving is different to me - not that one is better than the other. But each is different to me in the exertion level that is needed to get to the water. I want to be as light as I can when I am climbing over jetties or trekking over sand. That said - I dont need more than 19 cu feet from 130 with a 5 min stop - if I go OOA the dive is over and I am coming up. But I am not thinking I am air sharing my pony on the way up - if I am that safety stop is most likely cut short...

 

[JohnN]

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.

Unless you're using the pony as part of your planned air supply, you're now starting to consider a double point-of-failure. Unless you're going to do a full risk analysis based on that assumption, I think you're not looking at the complete picture

 

[doctormike]

Unless you're using the pony as part of your planned air supply, you're now starting to consider a double point-of-failure. Unless you're going to do a full risk analysis based on that assumption, I think you're not looking at the complete picture

Correct. But as I was saying, since there is no particular downside of a 40 compared to a 13 in my opinion, and since you never know what might happen (say, free flow when you are handing off a pony to another diver, etc..), the risk-benefit analysis to me seems to suggest that a 40 is the "sweet spot", and not the 13.

 

[JohnN]

Correct. But as I was saying, since there is no particular downside of a 40 compared to a 13 in my opinion, and since you never know what might happen (say, free flow when you are handing off a pony to another diver, etc..), the risk-benefit analysis to me seems to suggest that a 40 is the "sweet spot", and not the 13.

Unless you plan on flying somewhere and diving. . .

 

[Brewone0to]

To fly with cylinders, you must remove the valve.
Easier rent a pony wherever you are headed.
the difference between a 30 and 40 is length/height only.
Unless you are pretty short, the 40 just clips off easier/better.
zero profile difference.

 

[uncfnp]

To fly with cylinders, you must remove the valve.
Easier rent a pony wherever you are headed.
the difference between a 30 and 40 is length/height only.
Unless you are pretty short, the 40 just clips off easier/better.
zero profile difference.

Actually, flying with a 13 cf is quite simple and much cheaper than the 10 dollars a day we had to pay for a pony before we started carrying our own.

Fortunately pony bottles come in many different sizes just as divers so it doesn't have to be one-size-fits-all or even one-size-is-best.

And as I have said before, it's true that in the water and properly slung, a 13 feels little different than a 40 but on land or a crowded boat the difference can be significant.

 

[Nemrod]

since there is no particular downside of a 40

Plenty of downside, weight, size, drag, packing, walking, entry, exit and reduced likelihood of actually bringing it along and there is simply no need for this much capacity. At this point might as well go with doubles. Diver dependent, realizing some folks are Hoovers, but I generally can do on a 63cf the same dive as many on an 80 or larger. I can hardly see carrying a 40cf auxiliary with my back gas a 63cf.

Maybe rather than thinking in terms of cf, think in terms of minutes of air remaining. If a diver can do the same dive as another on 2/3 the air, why should they not consider a smaller auxiliary bottle (and back gas)? The two divers, the Hoover and the Miser, have the same minutes of air remaining. Divers on a single 80cf tank routinely end their dives at 700psi and seem to survive, why the need for such high capacity auxiliary tanks?

As far as planning for a buddy, let's see here. You have had a failure therefore you go to your auxiliary tank. So to plan for your buddy also you would have to have double the capacity in the aux bottle but that requires a DOUBLE failure, you and your buddy have to loose your main supply and then does the buddy have an aux bottle? if so we would need a TRIPLE failure before both of you wound up on your aux bottle.

And solo, I keep 1/3 in reserve, considering approximately 1/3 out and 1/3 back. I have been told this is overly conservative and often in fact it is and I apply the Rule of Thirds to fit the situation, not as an absolute. Why does a solo diver need to keep more than 1/3 in reserve? Therefore a pony sized to approximate the 1/3 capacity of the back gas bottle, enough is simply enough.

I am planning a dive this summer, a shore dive solo, depth probably no more than 30 feet. But there will be a half mile walk possibly and then a half mile swim. Do I really need to tote a 40cf aux bottle for a dive I can do near two hours BT on my 63cf? In fact, I may not use any aux bottle.

If folks need that much air, by all means satisfy the air lust but do not make the mistake of thinking that it is justified for all divers if even the majority of divers.

These aux bottle arguments go on and on, it is almost like thinking that a diver with manifolded twins need to actually have manifolded triples so they can have 50% of their main back gas on reserve. But then would they not need a fourth bottle 50% of that? I know, I am being ridiculous, but where does it end?

N

 

[mick allein III]

I am with doctor mikes post. I dive solo with a 40. I hardly know it's there. It's adequate for all rec depths, good resale value, and if you go tech will be very useful. I have a 19cf but prefer the Al40.


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[uncfnp]

...//... I dive solo with a 40. I hardly know it's there...//...


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I wonder if the other divers on the boat know it's there. Assuming it is a boat dive of course...

 

[doctormike]

Unless you plan on flying somewhere and diving. . .

Every time I have used a pony on an away trip, I rented it there. But I guess you could carry it with the valve out and find a shop to do a VIP once you get there too...

---------- Post added May 19th, 2015 at 10:23 PM ----------

Plenty of downside, weight, size, drag, packing, walking, entry, exit and reduced likelihood of actually bringing it along and there is simply no need for this much capacity. At this point might as well go with doubles. Diver dependent, realizing some folks are Hoovers, but I generally can do on a 63cf the same dive as many on an 80 or larger. I can hardly see carrying a 40cf auxiliary with my back gas a 63cf.

Maybe rather than thinking in terms of cf, think in terms of minutes of air remaining. If a diver can do the same dive as another on 2/3 the air, why should they not consider a smaller auxiliary bottle (and back gas)? The two divers, the Hoover and the Miser, have the same minutes of air remaining. Divers on a single 80cf tank routinely end their dives at 700psi and seem to survive, why the need for such high capacity auxiliary tanks?

As far as planning for a buddy, let's see here. You have had a failure therefore you go to your auxiliary tank. So to plan for your buddy also you would have to have double the capacity in the aux bottle but that requires a DOUBLE failure, you and your buddy have to loose your main supply and then does the buddy have an aux bottle? if so we would need a TRIPLE failure before both of you wound up on your aux bottle.

And solo, I keep 1/3 in reserve, considering approximately 1/3 out and 1/3 back. I have been told this is overly conservative and often in fact it is and I apply the Rule of Thirds to fit the situation, not as an absolute. Why does a solo diver need to keep more than 1/3 in reserve? Therefore a pony sized to approximate the 1/3 capacity of the back gas bottle, enough is simply enough.

I am planning a dive this summer, a shore dive solo, depth probably no more than 30 feet. But there will be a half mile walk possibly and then a half mile swim. Do I really need to tote a 40cf aux bottle for a dive I can do near two hours BT on my 63cf? In fact, I may not use any aux bottle.

If folks need that much air, by all means satisfy the air lust but do not make the mistake of thinking that it is justified for all divers if even the majority of divers.

These aux bottle arguments go on and on, it is almost like thinking that a diver with manifolded twins need to actually have manifolded triples so they can have 50% of their main back gas on reserve. But then would they not need a fourth bottle 50% of that? I know, I am being ridiculous, but where does it end?

N

Yeah, you are right. 40 is too big.