Pony Bottle / Stage Bottle / Decompression Bottle. What's the difference?

[broncobowsher]

An AL80 (which is actually less than 80), planning a rock bottom return of 500 PSI per normal training. That is 13is cubic feet of gas.
Are you telling me that if you saw 500 PSI in an AL80 in a normal no stop recreational dive you can't make it to the surface? An AL40 as a bail out, would be more than half of your back gas, just to surface.

The 6 might be a little small, if you were really deep. If you can't make a decent recreational ascent on a 13 you should not be diving or you are not doing a recreational dive.

 

[Angelo Farina]

In all cases I used a "pony", the plan was NOT to use it, except in case of a true emergency. Which fortunately never occurred. Having a customer low on air, and giving him my secondary reg with long hose, is not a "true emergency" for me, it is just an "inconvenience", something which does not need to use the pony.
So I want my main tank to be equipped as normal (primary+secondary), and use them "as normal", as if I had no pony tank. The pony is there for additional safety, "just in case"... And is to be used as a last resource, not as the first one.
If it is not "additional" but a "replacement" for my secondary, I do not perceive it as an increased safety tool, just as a different safety tool, not necessarily better.
So my approach is simple: I use a standard setup which I consider "safe enough" for most situations (15 liters main tank, with two independent regs on two posts). When I perceive the need of "additional safety", then I also carry a pony tank, as something ADDED to the standard equipment.
Reducing the capabilities of the main tank, by removing one reg, would result actually in a situation which is not safer than the starting point, despite having a pony tank...

 

[tbone1004]

An AL80 (which is actually less than 80), planning a rock bottom return of 500 PSI per normal training. That is 13is cubic feet of gas.
Are you telling me that if you saw 500 PSI in an AL80 in a normal no stop recreational dive you can't make it to the surface? An AL40 as a bail out, would be more than half of your back gas, just to surface.

The 6 might be a little small, if you were really deep. If you can't make a decent recreational ascent on a 13 you should not be diving or you are not doing a recreational dive.

enough to make a direct ascent to the surface, yes. Enough to resolve a problem, return to the anchor line, make an ascent, and complete a safety stop? Absolutely not.

@EFX if it's enough, then why bother switching back or having the secondary second stage in the first place? I stand by @RyanT that while it may not seem complicated, it is more complicated and does not provide any meaningful benefit, so there is no point. Same reason we don't have 2 SPG's on a set of doubles, or a spare wing inflator, or anything else that isn't complicated but doesn't bring any meaningful value and adds complexity.

 

[rongoodman]

An AL80 (which is actually less than 80), planning a rock bottom return of 500 PSI per normal training. That is 13is cubic feet of gas.

Whose "normal training" would that be? Every boat that I've ever been on wants me back on deck with 500 psi, not beginning my ascent with it.

 

[broncobowsher]

Whose "normal training" would that be? Every boat that I've ever been on wants me back on deck with 500 psi, not beginning my ascent with it.

That's my point. Be on the deck with 500 PSI, 13CF. That should be your minimum planned reserve back on the boat. So why isn't that minimum planned reserve enough for a pony? That reserve is there for reasons like having to share air at the last second at the bottom and get someone to the surface. Your plan is to return with 500 so you have that 13 CF for an emergency. Why does the pony need to be larger than the standard reserve capacity?

To be full disclosure I have never dove with a pony. Deco, stage, bailout, yes. Only know one who runs a pony.

 

[tursiops]

That's my point. Be on the deck with 500 PSI, 13CF. That should be your minimum planned reserve back on the boat. So why isn't that minimum planned reserve enough for a pony? That reserve is there for reasons like having to share air at the last second at the bottom and get someone to the surface. Your plan is to return with 500 so you have that 13 CF for an emergency. Why does the pony need to be larger than the standard reserve capacity?

To be full disclosure I have never dove with a pony. Deco, stage, bailout, yes. Only know one who runs a pony.

You may be confused. Returning with 500 means on the boat, not leaving the bottom. If you leave the bottom with 500, sharing air, you might not make it back. From 100 ft you won't.

 

[James79]

You may be confused. Returning with 500 means on the boat, not leaving the bottom. If you leave the bottom with 500, sharing air, you might not make it back. From 100 ft you won't.

I believe that what @broncobowsher is getting at, is that if I am about to start my ascent planned to have 500 psi on the boat, and you approach me out of air... that 500 psi (13cf) is there for you... to get you to the surface. Same as a 13cf pony. If a 13cf planned reserve in my main tank is sufficient, then why isn't 13cf reserve in a separate tank sufficient? Just playing devil's advocate... I have an AL19 that I use on shallow benign dives.
Respectfully,
James

 

[tursiops]

I believe that what @broncobowsher is getting at, is that if I am about to start my ascent planned to have 500 psi on the boat, and you approach me out of air... that 500 psi (13cf) is there for you... to get you to the surface. Same as a 13cf pony. If a 13cf planned reserve in my main tank is sufficient, then why isn't 13cf reserve in a separate tank sufficient? Just playing devil's advocate... I have an AL19 that I use on shallow benign dives.
Respectfully,
James

Firstly, he was talking about feeding TWO divers from that reserve.
Secondly, the magic 500 psi number is not a reserve, it is a safety margin on two things: accuracy of your pressure gauge, and giving enough pressure so your second stage will work (nominally 135 psi). It has the additional benefit of making sure no water gets into the tank, which can happen if it goes to empty.

 

[James79]

Firstly, he was talking about feeding TWO divers from that reserve.
Secondly, the magic 500 psi number is not a reserve, it is a safety margin on two things: accuracy of your pressure gauge, and giving enough pressure so your second stage will work (nominally 135 psi). It has the additional benefit of making sure no water gets into the tank, which can happen if it goes to empty.

Again, I have no dog in this fight.... just playing devil's advocate. To address the first point... I presented how I read his post, only @broncobowsher can definitively tell us what he meant. To address the second.... By that reasoning, the 500 psi on the boat rule common in recreational diving leaves zero reserve, and in the scenario I presented (starting my ascent to reach the boat at 500 psi) if you approached me OOA, then you would assume you are SOL? Please believe me, this is not meant as snarkiness. Just trying to get all the viewpoints. Also, a downstream second will function all the way down to ambient pressure... it will just get harder to draw the further below intermediate pressure you go. If you don't believe me, disconnect it from the LP hose and breathe from it while it is supplied by the ambient pressure in your living room.
Respectfully,
James

 

[rjack321]

An AL80 (which is actually less than 80), planning a rock bottom return of 500 PSI per normal training. That is 13is cubic feet of gas.
Are you telling me that if you saw 500 PSI in an AL80 in a normal no stop recreational dive you can't make it to the surface? An AL40 as a bail out, would be more than half of your back gas, just to surface.

The 6 might be a little small, if you were really deep. If you can't make a decent recreational ascent on a 13 you should not be diving or you are not doing a recreational dive.

If you are at 115ft and all that you have left is 500psi in an al80 - you are not in a good spot.
If you are climbing the ladder onto the boat with 500psi in an al80 - you're fine.