use to have a pony liked it but never pushed the limits and always have a buddy close by and was abvle to sell the whole thing at a good price so the money went to my new custom trailer to pull behind the wing can get gear for 4 dives in it easyly.
I typically dive with a 20 cubic foot pony. It is strapped to my primary tank. I have never actually needed it and plan on never needing it (which is why I have it). I used to have a 13. I found that it would lose an unacceptable percentage of it's gas just over the course of turing it on. When I dive with a pony I ALWAYS turn the air on BEFORE diving. After about a half dozen dives I'd need to fill the tank. The twenty gives me a lot more air (in case I ever do need it), and I have to fill it less frequently.
Good to see an old thread revisited! When I did my advanced cert I had a freeflow in superior at 90' and 39 degree water. I had my Regulator set to give me all the air I wanted and of course it did (Yes, I was as nervous as a preacher in a porn shop ). Moisture built up and the 2nd stage froze up. This was a high perf reg/cold water reg. But it happens and will happen again. My Buddy/Instructor had his Pony and we were able to abort safely and even complete the safety stop. So after that incident I bought one and will always carry it on advanced Dives. I bought the 30 as the difference in price is minimal and I'll take the air. For mounting I started out with the back tank mount and last year switched to the staged D-Ring Method. I won't be going back.
You do want to pressurize your pony before Diving (test it like you would your other regs.) I got sloppy and just dragged it along on a dive. Having no pressure to the 2nd stage allowed water to creep up the hose. While reorganizing my gear (this winter)and checking tank pressure I found out that water was still trapped behind the valve seats.. Well. thank goodness for Dive Stores and maintenance. Call it another lesson learned.
good discusion about the pony bottles.
I dive frequently in Superior and almost always bring mine on penetration dives. Personally I like mine on my back, one less thing do mess with during the dive; however it does limit the size of holes that I can squeeze through. A couple of points though.
1. Do not use it as a way to extend your bottom time. Had a buddy do this once and he said he nearly drowned.
2. When picking the size you want, get what you want. You can easily get by with a smaller tank, because you can breath for quite awhile from a free flowing reg. I don't know the details, but even from a 13cf bottle you should be able to ascend from a decent (100+ ) depth and still include your safety stop.
Maybe someone with more experiance.. but my calculation and RMV (SAC) is .9 if I'm tense and 13cf to get me from 100 has some pucker-factor.
60ft/min from 100 to 60ft and then 30ft/min to 15 +3min + 1min to surface (don't want to rush the last 15)
I calculate that I would need 13.5 cf, that's too tight for me. I'll round that up to 40cf
Did I blow the math? I did it in my head so there is a lot of rounding.