Back mount pony bottle

[Angelo Farina]

If a diver breathes off a pony to extend a dive, relying on the reserve in the main tank to get to the surface and then experiences a primary regulator problem or blown hose, they are in the same exact situation as the typical diver who uses only one tank.

In other words, extending a dive using a pony bottle, while leaving the typical reserve in the main tank does not create any additional risk, while giving the benefit of having redundant air during most of the dive (prior to extending it with the gas in the smaller tank).

The additional risk arises if the primary tank has only one main reg and no secondary reg. Most people using a pony install only a single reg on the main tank. I instead always use two (complete, two first stages, two second stages, on two independent valves - and my main 15-liters steel tank has also the reserve).
So, when using a pony (not always, in my case, but only for "heavy tasks"), I end up with THREE complete and fully independent regs, each with its own valve.
At that point, however you use your pony, it does never diminish safety compared to not having it.
But if the pony means moving the secondary reg from the main tank to the small bottle, then you could have a problem: if the primary reg fails, you have no backup on the main tank...

 

[Angelo Farina]

So what’s the optimal size for a back
mounted stage used to extend the dive at 100ft? Is a 9cf enough or do I need a 13cf?

I do not really understand what those "cf" mean. I use a 3 liters pony at 200 bar (600 liters total).
Typically I attach it in the middle of my twin tanks (2x 9 liters at 200 bar), or beside my single tank (15 liters at 232 bars). In both cases the main tank has two independent valves, two fully independent regs and reserve.
This is a good redundancy, in my opinion, for demanding dives (when crossing the border to tech, which in reality I did in the past only a very small number of times and I am not doing anymore in the last 25 years).
But here we are in "basic scuba" forum, so I understand that my pony setup is "overkilling" here...

 

[34109411]

I do not really understand what those "cf" mean. I use a 3 liters pony at 200 bar (600 liters total).
Typically I attach it in the middle of my twin tanks (2x 9 liters at 200 bar), or beside my single tank (15 liters at 232 bars). In both cases the main tank has two independent valves, two fully independent regs and reserve.
This is a good redundancy, in my opinion, for demanding dives (when crossing the border to tech, which in reality I did in the past only a very small number of times and I am not doing anymore in the last 25 years).
But here we are in "basic scuba" forum, so I understand that my pony setup is "overkilling" here...

Cf : cubic feet

 

[jborg]

I do not really understand what those "cf" mean. I use a 3 liters pony at 200 bar (600 liters total).

Sorry, I was attempting a humorous mix of the countless pony threads currently ongoing with the “stage and pony only differ in the name” post above. I realise it was a failure.

 

[scubadada]

Cf : cubic feet

Sorry, imperial

1 cubic foot = 28.3 liters
1 liter = 0.035 cubic feet

Average Gas Consumption

There has been extensive discussion lately regarding average gas consumption. A poll may help give us a better idea of what the normal distribution of RMVs is. 1 cu ft = 28.32 liters 1 liter = 0.035 cu ft 28.3 l/min

scubaboard.com

 

[Fishdip]

I always use a pony "40cf" even when I dive side or doubles, I will have a pony with a first stage and a drysuit inflator. Not only does it make launching a SMB really easy but if you ever have a situation and you or another member of your team is out of air for any reason being able to unclip and pass it to them is far better than having to hold hands. It also gives them the ability to use the hose for BCD/dry suit inflation at the end of the day I rather have extra air then no air. It's also why I moved away from the smaller back mount pony rigs as you cannot pass them.

 

[grf88]

I always use a pony "40cf" even when I dive side or doubles, I will have a pony with a first stage and a drysuit inflator. Not only does it make launching a SMB really easy but if you ever have a situation and you or another member of your team is out of air for any reason being able to unclip and pass it to them is far better than having to hold hands. It also gives them the ability to use the hose for BCD/dry suit inflation at the end of the day I rather have extra air then no air. It's also why I moved away from the smaller back mount pony rigs as you cannot pass them.

I like the idea of adding an inflator.

 

[vespers_]

I have a back mounted 19cf pony. I attached it by placing 2 hose clamps around it to hold a metal bar, and then slid a tank strap between the bar and pony. The whole thing just slides right on to the main tank like you would attach your main tank to your BC.

I really like it. I don't notice it in the water at all. It has basically no affect on dives and is only marginally heavier on land.

I don't see the appeal of dangling things off my body with a sling, especially given the high current where I'm from. I have no interest in sidemounts either.

I've never actually had to use the pony and probably never will, but it is there if I do. It seems like a pretty small tradeoff to me.

 

[34109411]

I have a back mounted 19cf pony. I attached it by placing 2 hose clamps around it to hold a metal bar, and then slid a tank strap between the bar and pony. The whole thing just slides right on to the main tank like you would attach your main tank to your BC.

I really like it. I don't notice it in the water at all. It has basically no affect on dives and is only marginally heavier on land.

I don't see the appeal of dangling things off my body with a sling, especially given the high current where I'm from. I have no interest in sidemounts either.

I've never actually had to use the pony and probably never will, but it is there if I do. It seems like a pretty small tradeoff to me.

i do have a 30 cf sling under my left arm. The setup i use is not dangling at all. All depend of gear configuration; size of bold snap, position of your the d-ring etc..I do respect your view !

 

[Stoo]

I have a back mounted 19cf pony. I attached it by placing 2 hose clamps around it to hold a metal bar, and then slid a tank strap between the bar and pony. The whole thing just slides right on to the main tank like you would attach your main tank to your BC.

I really like it. I don't notice it in the water at all. It has basically no affect on dives and is only marginally heavier on land.

I don't see the appeal of dangling things off my body with a sling, especially given the high current where I'm from. I have no interest in sidemounts either.

I've never actually had to use the pony and probably never will, but it is there if I do. It seems like a pretty small tradeoff to me.

I used your setup for years and it’s a simple way to carry a little bit of redundancy. The only issue is simply that a 19’ bottle won’t last long at a serious depth.

A 19 would be had to sling and the 40s are easier to sling and have the advantage of being able to see the valve etc.

If your diving isn’t deeper than 100’ or so, your setup will do the job. Just be sure to check the tank is full before each dive.