Optimal Pony Bottle Size for Failure at 100ft?

[broncobowsher]

Since you have a borrowed pony, take it for a test dive. Next time you are out, switch to it just before ascent. Putz around for a minutes or so. Surface. What do you have when done? There is still your primary you can always go back to.

 

[VikingDives]

If you're thinking about buying a pony, there are probably 100 threads about the overall advantages of a 40. In the long run, it's probably a better option...

 

[lowwall]

I used [a 6 cu ft pony] (for real after foolishly sucking the main tank down to close to zero) in 130 and switched over, started my ascent, then dropped something and watched it fall away to the bottom and I knew there was no way I could chase it with the 6 cuft tank and it was lost forever. I sure wished I was smarter (and had a larger pony bottle) that day.

So an advantage of a minimum sized pony is that it keeps you from compounding your bad decisions with worse decisions?

 

[scubadada]

If you're thinking about buying a pony, there are probably 100 threads about the overall advantages of a 40. In the long run, it's probably a better option...

Way bigger than I need, twice as big.

 

[ps444mike]

Great job on the figures.. but depening on whats happening and where your dive buddy is you might be able to use the pony to get to them and work your way back up.. or hopefully your buddy will see you going up and come up to check and or assist you..

 

[johndiver999]

So an advantage of a minimum sized pony is that it keeps you from compounding your bad decisions with worse decisions?

Well it may serve to preclude a person from making the same bad decisions twice (and it can also get you out of any additional car & mortgage payments, too).

 

[VikingDives]

Way bigger than I need, twice as big.

Me too, but take the me out of it and there's a lot of reasons to buy a 40

 

[SlugLife]

The optimal size of pony-bottle when dealing with a failure is....

1. The one actually on your person (and not left at home)
2. The biggest one possible.

If your pony-bottle is big enough that you get lazy and leave it behind, as I've seen many divers do, it doesn't matter how big that pony bottle is, when you have a failure, and don't have any redundant air with you. I'd rather have a 6cu at 100ft, than nothing (and would probably survive).

Next, if we assume a failure WILL happen at 100ft (rather than might happen) then you'll want all the extra air you can get. One scenario where this may apply, is right after you serviced your regulators, or if you're testing out sketchy regulators (that said, you may want 2 redundant air sources if you presume failure is likely).

----

But lets go to a more "normal" scenario, where failure is unlikely, but the cost of being unprepared in that unlikely scenario is high. You need to look at your air-consumption back up to the surface. That greatly depends on:

• Whether anything else goes wrong, such as an entanglement
• Environmental conditions, such as overheads, visibility, temperature, current, etc.
• What your personal air-consumption is
• Whether you are prone to panic

For me, I usually dive with a 19cu, and I've calculated and TESTED (it's useful to actually do a test run surfacing on your pony) at 120ft. That said, it was an ideal test environment, no panic, no risk, no entanglements, no currents, etc. Usually, once I'm past 80ft, I upgrade to a bigger size (usually sidemount, double 80cu) because I can. I'd be okay with using a 19cu at 100ft, but I usually prefer larger at 100ft. If we pretend I'm not sidemount, I'd probably look at a 30cu or 40cu for 100ft.

 

[SlugLife]

After switching to pony bottle, I will probably need 2-3 mins to compose myself and think about my situation

If you switch to your pony, immediately and calmly begin ascending. It should be "automatic". The only 2-3 minutes might be dealing with another hazard, such as an entanglement, which is worth considering (an entanglement may trap or damage your main regulator).

it will only be used in emergencies and never to otherwise extend bottom time

For actual pony-bottles, of course. But dive-extending may be worth considering. Because I switch to sidemount (or independent doubles for BM) when I'm approaching or exceeding 100-feet, I can switch between tanks, use it as a dive-extender, and either tank is always capable of getting me safely to the surface.

3. Safety stop

Safety stops are ideal, but optional and can be skipped if needed.

4. Final exit and swim to the boat

Calculating needing air on the surface seems a little odd to me.

Is my logic correct here? Any other insight would be greatly appreciated.

40cu can't hurt, assuming you reliably bring it on every dive. I think your calculating quite far on the "safe" side, which isn't a bad thing to do. If you had 40cu, it might also be great for dives that occasionally go to 120ft or so.

 

[wetb4igetinthewater]

@chrisjur

Are you able to access this?