Should we get pony bottles?

[Lorenzoid]

A couple of years ago I went through a phase where I had convinced myself I wanted a pony bottle for my diving, especially the 5% of the time when I find myself with an insta-buddy. But the more I read here, the more it seemed that the better route for me--and my wife, who is my buddy 95% of the time--is to adopt gas planning principles and the philosophy that each of us is carrying the other's back-up gas. We are not photographers, but letting photography or anything else take precedence over good buddy habits seems like a bad idea.

A pony could be useful for the 5% of the time I dive with an insta-buddy, or for when we are ambushed by a divemaster's decision to take us closer to the limits than what we had planned. Sure, if we could plan 100% of our dives ourselves and dive our plan 100% of the time, we wouldn't need a pony, but that's not always the case when doing a DM-led dive. However, the negative I see in taking along a pony for only some of our dives is that (a) we don't always know in advance which dives will take us close to the limit, so we might possibly end up not taking it along when we should have, and (b) switching gear configurations isn't appealing to me; I want to use the same configuration on every dive to the greatest extent possible.

 

[uncfnp]

And here is my take.

Eric and I are not always good buddy's. We both hunt, I occasionally do photography, and it is almost impossible to get Eric's attention underwater, even if he is only a few feet away. And for health reasons, I do not want to be in a situation where I need to omit the safety stop much less do a CESA, even on rec dives. And we often solo.

We chose to sling small ponies. I carry a 13 cf. And yes you can sling it with a regular, back inflate BCD. I sling mine on my Oceanic Islander, about as lightweight and nontechie as you can get. There are no D rings but there is a loop at the left shoulder that I attach a Quick Link to and another link to a loop at the left hip. Then just clip in the rigging for the sling. During a recent trip, I actually slung a 40 this way, no problems. Yes, we are often the only divers on the boat with redundancy. We do get comments and questions. On the surface, it is a hassel. Under the waves, I don't even know its there. It is absolutely worth it.

No, we have never needed them and unless there is an equipment malfunction, we never should. We do not use them to extend the dive though the reality is that we might push the limit a little more because we know its there (why do you always see that monster lobster at the end of a dive?). They are there for redundancy only.

If you know your buddy will always be within a few seconds reach, know you are both obsessed with gas management and will never make a mistake and you both are willing to accept the very small risk of an equipment failure and a CESA or buddy breathing, or if most of your diving will be travel where you are not planning to take the bottle (though depending on location you might be able to rent a small tank) then no, a pony is a waste of resources,

 

[flots am]

first time i've heard of this... is there any reason for that limit (1cf per foot)?..

It's a very old "rule of thumb" to not dive deeper than the number of cubic feet in your tank and went along with "don't ascend faster than your smallest bubbles"

The first time I ran across it was from a book from the 60's or 70's.

It's nice for new divers who want a sanity check on a deeper dive, but isn't anything I'd use for actual gas planning.

The other problem is that it's routinely ignored, and tons of dives more than 80' are done on resort areas where the only available tanks are 80's.

 

[T-Wrecks]

To answer your question you need to calculate the minimum amount of gas needed for 2 divers to safely ascend.


If you do the math, it may help you ascertain whether you are diving with enough gas, so here we go:


For your 110ft dive, lets set your average depth at 50ft for this exercise.


average ATA (50ft) = 2.5
sac rate = 1.0 (calculating for panicked rate)
time to ascend = 8.5 minutes (x2, to calculate for your buddy) = 17 minutes
Gas needed for 2 divers to ascend = 42.5 cubic ft
Converted to PSI in a single AL80 = 1700psi


This gives you 1300psi of usable gas for the dive, meaning you need to be on the surface with 1700psi remaining in the tank.


If this is not the case, then you need to bring more gas, or change your dive plan to accommodate the amount you intend to bring.

 

[DivemasterDennis]

Here is my contribution to the op's decision process: Neither I (almost 1000 dives) nor my wife ( over 250 dives) have ever carried a pony bottle on a recreational dive. We usually diver AL80s, sometime steel tanks a little smaller. We are both good on air, and we check air supply often. Debbie in particular has a very low air consumption rate, yet I have yet to "borrow" from her. We have friends who we consider very good divers and who are very experienced divers who will not dive without a pony bottle. That is their preference. Who is right? I think we both are, becasue we dive with equipment with which we are comfortable as being proper for a safe recreational dive. Let's make that clear, recreational dives. If you talk overhead environement, deco dives, or beyond recreational limits, then a whole new array of equipment comes out.
DivemasterDennis

 

[drbill]

Although I mostly dive solo, I use my pony even when buddied up since I'm usually diving with another photographer. We may be too busy imaging something to notice an issue and too far apart to make it easy to assist one another.

For me diving with a pony has almost nothing to do with running out of air (I manage my gas very well... I've had a LOT of practice). It is about potential emergencies that might require a redundant air source. For example, the dip or debris tube in my 80 cu ft main tank once clogged at a depth of about 80 ft and no air came out of the valve period. It was one of the few deep dives where I hadn't mounted my pony. Potential equipment failure and solo diving are the reasons I dive with a pony.

 

[phoenix31tt]

To answer your question you need to calculate the minimum amount of gas needed for 2 divers to safely ascend.


If you do the math, it may help you ascertain whether you are diving with enough gas, so here we go:


For your 110ft dive, lets set your average depth at 50ft for this exercise.


average ATA (50ft) = 2.5
sac rate = 1.0 (calculating for panicked rate)
time to ascend = 8.5 minutes (x2, to calculate for your buddy) = 17 minutes
Gas needed for 2 divers to ascend = 42.5 cubic ft
Converted to PSI in a single AL80 = 1700psi


This gives you 1300psi of usable gas for the dive, meaning you need to be on the surface with 1700psi remaining in the tank.


If this is not the case, then you need to bring more gas, or change your dive plan to accommodate the amount you intend to bring.

actually for typical gas planning I use a rock bottom formula and i spit out some figures so that i can adjust at depth... it looks like:

Depth	Rock Bottom PSI
<40	500
<60	800
<80	1100
<100	1400
<110	1700
<130	2300

typically we dive lots of walls and fringe reefs, so lots of flexibility in terms of depth... so what i do, when i hit rock bottom for a certain depth, i move up to a shallower depth, until i hit rock bottom for that depth, for me i think it's the most efficient way to safely dive rock bottom (i'm open to correction)... i must admit that i do "cheat" sometimes because in my RB calculations i have a 200psi built buffer... so at 80' i wont make it a big deal to stay till 1000psi


good advice all around guys, lots of considerations... If i were to decide now, the way we dive... i may still be leaning towards not getting it... however, the situation may change with two cameras (although i dont think i'd put a shot over our safety, but you never know until you are in the situation)... keep throwing out advice, still some time before i have the funds to make the decision neway

 

[kwinter]

Just piling on to what's already been said. A pony has nothing to do with having more gas. Anyone who suggests a larger primary tank instead of a second supply doesn't know what he's talking about and should be avoided. As you suspected, it is about redundancy. You do not calculate the gas in the pony into your dive plan.

And personally I think you should each get one. Redundancy is great. Self sufficiency is even better. You could get separated. One of you could be helping another diver and then the other one has a problem. You never know when self sufficiency comes into play.

As for size and mounting it on your primary vs. slinging, that is a personal choice. Some folks don't like having a tank front mounted or even sidemounted. Others find it easy to control. Some are uncomfortable with less than a 40 cf tank, others are fine with a 1 cf Spare Air. Most think of having at least a 13 cf tank mounted to the primary, or at least a 30 slung. Either way, the cost of the tank is minimal compared to the need for a second complete reg. I would prefer to either sling it or use a quick release system for mounting so that the entire thing can be donated.

Just my $0.01 (50% discount today)

 

[rx7diver]

A pony has nothing to do with having more gas. Anyone who suggests a larger primary tank instead of a second supply doesn't know what he's talking about and should be avoided. As you suspected, it is about redundancy. You do not calculate the gas in the pony into your dive plan.

kwinter,

I don't think you'll find universal agreement with what you've written, though I've seen this written before.

A recreational, open-water diver who is buddy diving may elect to carry his/her emergency reserves in his single back tank. Alternately, a recreational, open-water diver who is buddy diving may elect to carry his emergency reserves in a pony bottle if his single back tank isn't large enough to accommodate these reserves.

There are other reasons for carrying a pony bottle, as well. Indeed, a recreational, open water diver whose single back tank is large enough to carry his emergency reserves may elect to also carry a pony bottle also containing his (duplicate) reserves.

At least, this is what I've observed in practice.

Safe Diving,

rx7diver

 

[Max Speed]

meaning you need to be on the surface with 1700psi remaining in the tank.
.

Or more reasonably... start towards the surface with 1700 psi remaining. You can arrive with 150 psi.


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