I have been doing my 70-90 foot controlled assents using a 30 cube pony. I have decided to go to something smaller. Do you know whether a 13 or 15 cube pony will carry me to the surface in an assent described above. If it did not I would switch back to the primary tank of course. I was just wondering if anyone out there has any experience with this?
The above post is correct, however the actual answer depends on the magic number: "Your stressed SAC rate"
You might be able to go to a smaller pony, but you might just as easily find that you can't, or you need a bigger one, and nobody can tell you what the answer is; you need to figure it out out for yourself, since it requires knowing how much air you actually use when stressed.
It's possible to guess at your SAC if you know your normal SAC, however there's no way to know if you should multiply it by two or three or even more to account for stress, since it depends on whatever event caused you to blow your dive plan and run out of air.
For example, if you're just watching pretty fish, forget to check your SPG, run out, and switch to your pony, you'll probably be pretty close to normal. If you're trapped in a discarded fishing net or lost inside a wreck and have spent the last 10 minutes looking for an exit or trying to cut away at a net you can't really see, you could be sucking air like an Electrolux (why let Hoover get all the credit?
).
This probably isn't the answer you're looking for, but at least it's something to think about.
Terry
