How many second stages when diving with a pony?

[Druid]

I'm curious about that statement. Why?
A pony is just a tank with some gas in. Who cares who breathes it. I can understand why someone might have a donation priority, octo before pony, but if someone needed air I can't think why I would differentiate and call some mine and some yours.

A proper gas plan has reserve volume in both the pony and the main tank. At the worst possible moment (max depth/max duration) you should have enough gas in either for ascent so who breathes what shouldn't really matter should it.

What's the rationale?

The pony is not included in the gas planning, it's there to get get you out of trouble if the **** hits the fan. We commonly use small 3ltr pony tanks which should be enough to get to the surface from 30m, but a stressed diver could easily empty it long before that. This would mean another reg switch which would likely not reduce stress levels or gas consumption. So the buddy is briefed to use the octo on the main tank, which does contain enough gas to get a stressed diver to the surface from 30m.

 

[drbill]

Personally, I dive with an octo on my main tank making a total of three second stages. I prefer to go from my secondary to my octo and then the pony in that order. Have only had to use the pony twice in all my years... once when my deco time exceeded my plan due to an unusual filming opportunity at depth and the other due to another unusual filming opportunity but in a non-deco situation at fairly shallow depth. As an almost strictly solo diver, I have never had to donate.

 

[uwxplorer]

Personally, I dive with an octo on my main tank making a total of three second stages. I prefer to go from my secondary to my octo and then the pony in that order. Have only had to use the pony twice in all my years... once when my deco time exceeded my plan due to an unusual filming opportunity at depth and the other due to another unusual filming opportunity but in a non-deco situation at fairly shallow depth. As an almost strictly solo diver, I have never had to donate.

I'll second that.
First because a bright yellow octo at the usual location is helpful for an OOA fellow diver in panic mode (you are not going to always be alone in the water). You don't want him/her to rip off the reg out of your mouth (which he/she might well do if coming from behind).
Trust me, a diver who has swam without air to get to you will grab the only thing he/she knows will give him/her air FOR SURE. First YOUR second stage and second, only if it is in plain sight (or you are handing it to him/her and have proven, by a purge, that it delivers air), your octo.
Second, you don't always want to abort a dive if you have an issue on your second stage (other than an uncontrollable free-flow).
Case in point: I have had a wet second stage on two occasions. You can't necessarily catch this problem at the surface, and you cannot always fix it underwater. I could have continued breathing it, but why should I have? What I did was just stow my main second stage away and used my octo. This were true solo dives. Had I had a buddy, I would have aborted to fix the problem.
SDI will teach you that your pony needs to be 1/3 of your main tank (which itself should allow you to follow the rule of third: 1/3 in, 1/3 back, 1/3 backup). So you end up with plenty of margin. You might be superhuman and extra lucky like some of the posters seem to think they are, but that's the 0.01% of the statistics that you want to be ready for.
Down there, with no air or no way to get it, you will die.

 

[Kharon]

1. The pony is not included in the gas planning, it's there to get get you out of trouble if the **** hits the fan.

2. Trust me, a diver who has swam without air to get to you will grab the only thing he/she knows will give him/her air FOR SURE.

Multiple quotes above that I agree with. 1 - My pony is dispensable. As long as my main tank/regs are OK I can hand off the pony - no harm, no foul. That air is some I never intended to use. 2 - definitely. But once the OOA diver is breathing there is no reason we can't switch and I can hand off my pony. I do not want to be tethered to a diver that went OOA. Better that I lose my pony than being dragged to the surface in an uncontrolled ascent.

3. A divemaster on Peace dive boat helped me set-up my pony bottle rig. He said: "the octo is for the other diver, and your pony rig is for you and only you!"

4. SDI will teach you that your pony needs to be 1/3 of your main tank (which itself should allow you to follow the rule of third: 1/3 in, 1/3 back, 1/3 backup). So you end up with plenty of margin.

Quotes above that I disagree with. 3 - bushwah!!! It's definitely not part of my dive plan. My pony is available for whatever emergency occurs. And finally, 4 - Not exactly (according to my experience). SDI proposes the 1/3 volume as the simplest way to calculate your redundant air. They promote the calculation of the needed redundant air from SAC, dive depth, and other factors. If your going to dive solo you should be able to calculate rather than use a very general rule of thumb. My redundant air needs are very different diving to 130 feet in cold murky water versus diving to 50 feet in warm water with 100 feet visibility.

 

[uwxplorer]

. My redundant air needs are very different diving to 130 feet in cold murky water versus diving to 50 feet in warm water with 100 feet visibility.

Precisely. Since you are most likely not using a different pony or tank depending on the planned dive, you should choose the ones that will fit your most demanding needs (unless you are talking about travel, in which case you are entering a whole different world of potential issues).

When I was diving OC solo, I was using a steel LP95 with a 30 cf pony and confining myself to ~100 ft deep dives max, with an average SAC rate of 0.5 cf/min. I would plan to turn the dive at around 1000 psi (the return path being usually shorter than the meandering way out - a LP tank can be filled to upward of 2600 psi) and would usually end up with 1000 psi or more after dives long enough for me to get either cold, bored or running into the risk of being scolded by the DM for delaying everyone.
The only times where I was glad I did not stray too far from that 'stupid' rule of third were cases where I could not find the up line in murky viz and experienced heavier breathing as a result. I was glad I had still some margin on my main tank, and plenty in my pony. In all cases, I came back up with more than 500 psi, but I was nonetheless upset because of my stupidity.
Also factor in the possibility that your SPG or AI computer suddenly gives you absurd (or no) readings, as it has happened to me. Normally, as a solo diver, this is a non-issue, as you know your SAC rate, depth, profile, the time in the dive, your latest reading, etc, so there shouldn't be any reasons to panic (in my case, I had a redundant readout, so it really never was an issue) .
But IF the situation is a tad (or very) challenging, as I described above, you can bet that your breathing rate is going to go up and the knowledge that you still have plenty of air to continue looking for the up line (or safely ascending in green water if needed in latest resort) is something that you are going to appreciate.

 

[scubadada]

Personally, I dive with an octo on my main tank making a total of three second stages. I prefer to go from my secondary to my octo and then the pony in that order. Have only had to use the pony twice in all my years... once when my deco time exceeded my plan due to an unusual filming opportunity at depth and the other due to another unusual filming opportunity but in a non-deco situation at fairly shallow depth. As an almost strictly solo diver, I have never had to donate.

I'm with drbill I do not change my regulator configuration whether I'm diving my pony or not

 

[DaleC]

The pony is not included in the gas planning, it's there to get get you out of trouble if the **** hits the fan. We commonly use small 3ltr pony tanks which should be enough to get to the surface from 30m, but a stressed diver could easily empty it long before that. This would mean another reg switch which would likely not reduce stress levels or gas consumption. So the buddy is briefed to use the octo on the main tank, which does contain enough gas to get a stressed diver to the surface from 30m.

I would challenge that thinking.

I think you meant not part of the ordinary gas consumption plan. The pony is part of gas planning. It falls under your plan for a redundant air supply, which also could include your buddies gas (or not). Would one feel comfortable diving a deep dive with a buddy that used a 63cuft tank because they had a low sac? No, we would expect the team to take appropriate gas for the dive. As such one needs to consider how much gas is needed for exit for that particular dive. Some require a smaller pony, some a larger one. I own two - a 19 and a 40.

For me, the pony should always hold enough gas for one diver to exit safely from max depth/duration, or rock bottom for the dive. Who's to say the primary diver won't be the stressed one? And if the pony is their primary bailout strategy, what alternate reg will they switch to?

Doing gas calculations shouldn't be a finely tuned process, so the buffer should fit most divers. Some teams approach exits differently (spearfishing vs rec etc...) but even then, I would think a team to be on the same page, exit strategy wise, during the same dive.

That being the case, it doesn't matter which diver (primary or buddy) uses the pony, it should have enough gas for either to exit.

 

[Searcaigh]

No octopus on my main regulator when I side sling my pony. I also dive long hose and ready to donate that second stage if required.