Back mount pony bottle

[GiraffeMarineSalvage]

Air is just fine. You are only going to use it when something has gone really wrong so no benefit to nitrox.

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

 

[johndiver999]

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

Trying to match the pony and main tank in composition means it needs to be adjusted every time you use a different mix. If that happens very infrequently, then no big deal. If it happens a lot, then you spend a lot of time and money adding and dumping gas from a pony bottle - which will probably never get used!

I top mine off with whatever tank I have on had and generally try to put the least rich mix in the tank. Using air makes things much simpler and I prefer to use air when available.

 

[Fishdip]

I don't disagree that given the short amount of time involved for a NDL ascent an air filled pony bottle is likely to be ok, but given how much EAN can impact deco obligations and what may be a faster than optimal ascent I would strongly prefer pony to have same mix simply for piece of mind given the grey areas involved in decompression sickness.

You would have 0 deco obligations if you are staying with in rec limits tho?

 

[GiraffeMarineSalvage]

You would have 0 deco obligations if you are staying with in rec limits tho?

True. But the rec limits are based upon going up slowly and generally a minimal "safety stop," both of which might not happen when using a pony bottle. Since some people get the bends after following all the rules (even though that is rare...) I personally like increasing safety margins if and when practical.
Johndiver999 brings up a very valid point of unnecessary costs if you chose optimal mix for a given depths and matched your pony bottle to that mix, but despite my not personally being a GUE diver I'm a huge fan of the standard gases they recommend for given depth ranges...

 

[happy-diver]

Yes carry some type nitrox in your pony for less nitrogen ongassing
paying attention to spg, enabling you to extend your stop if desired
without having to wonder how long before you feel a sudden clunk
from your completely empty regulator

 

[SlugLife]

We talk about "trust me" dives in a negative connotation. Trust me dives are bad. The reality is any non self redundant dive is a trust me dive. All of the agencies teach trust me dives from the very beginning of confined water.

I'm unfamiliar with this term. I'm guessing it means "Trust me, I won't put you in danger, and will be there to rescue you in an emergency?"

IMO, a safety-minded diver treats insta-buddy-dives as "a solo-dive with a buddy-hazard" and recognizes there are many scenarios where their buddy may be unable to assist.

Air is just fine. You are only going to use it when something has gone really wrong so no benefit to nitrox.

Trying to match the pony and main tank in composition means it needs to be adjusted every time you use a different mix. If that happens very infrequently, then no big deal. If it happens a lot, then you spend a lot of time and money adding and dumping gas from a pony bottle - which will probably never get used!

I top mine off with whatever tank I have on had and generally try to put the least rich mix in the tank. Using air makes things much simpler and I prefer to use air when available.

^ Basically this. I top-up my pony from my main tank each dive, and there's no (meaningful) benefit to having nitrox in an emergency-only pony tank intended for recreational depths. The transfill setup also offers the advantage of being able to practice switching each dive, taking a few breaths, and leaving the cylinder open. And if I top up a pony with a couple-hundred-psi of nitrox, once or twice, I won't lose any sleep over it.

If you start getting into technical/deep, then you'd plan your redundant-gasses, such that you could safely surface in the event that any tank or regulator failed. At that point, it's usually no longer called a "pony bottle", you're probably looking at 30-or-more cu and much of the previous discussion in this thread become inapplicable.

 

[gamon]

I use a 30 cf pony bottle strapped to my back via a mount on the BCD tank strap. Its upright and always on during the dive, I monitor the pressure using a tank transmitter with a receiver on my left wrist (my right wrist has the receiver for my main tank).

The 2nd stage pony regulator is on a rubber necklace just below my chin.

Advantages- tank is always on and monitored so no surprises and if needed in an emergency I don't have to reach behind and down and fumble with the valve.

I "use" the pony bottle on each and every dive, even if I don't draw a single breath - I allow my main tank reserve to get several hundred psi lower than normal since I have the reserve in the full pony, thus extending each dive by several minutes, while also having the redundant gas throughout the dive.

I used to carry an air2 now I have no octopus reg. If shallow solo diving in no overhead environment I usually don't take the pony bottle.

The only disadvantage is that the pony can interfere with the BCD rear inflate bladder, so it's a bit tricky to maintain proper trim and not roll, even with offset compensating weights I end up with more air on the side without the pony and tend to get an air bubble that rolls around a bit from time to time.

For recreational depths there's no good reason for filling the pony bottle with Nitrox. If needed at depth you won't be breathing it long enough to be an issue with CNS toxicity even if you momentarily exceed the MOD.

 

[bradlw]

that, & I would add that the MOD is fuzzy anyway....it's based on a particular PO2 target and you can go with a higher PO2 for the calculation and get a larger MOD number
so
on the question of Nitrox I'd prefer to have Nitrox on board for the added safety factor...emergency and the elevator is going up...maybe a little faster than ideal, etc... + in the even of a DCS situation the faster you go on O2 the better and going on Nitrox for the elevator ride up is just a little closer to O2 than air.... if that makes sense

 

[MaxBottomtime]

How often are you people using a pony if you have to top it off after every dive?

 

[Boarderguy]

How often are you people using a pony if you have to top it off after every dive?

Every dive I take a few breaths off mine before I splash to ensure it's functioning. I also check pressure before I leave the house. Both of those actions add up over a few dives and need for the bottle to be topped back up from ~2800 to 3000-3100. Any use during the dive for muscle memory also depletes it. Transfer whip saves time. My lds tops off no charge as well if I remember to bring it with me.