ReefHound:
But this is a reason of convenience, not safety. I'm thinking that getting in the second dive is not all that critical when the first dive ended with an OOA incident. But if it is, just bring an extra pony bottle.
Not all OOA incidents are the same. If a yoke face O-ring blows and we have to call the first dive short, that has very little, if anything, to do with the second dive. We're not going to be using the same tanks for the second dive, and our nitrogen loading is going to be lower than it would have been had the dive not been shortened. If a first stage went kaput, that'd call the day, but for a simple problem like an O-ring, we'd just do the same air sharing ascent we've practiced umtpeen and a half times.
Sharing air is a perfectly logical course of action for a gear failure at depth, and sharing back gas between two divers of an experienced buddy pair is hardly a big deal. With that in mind, preserving redundancy is hardly a pointless concept.
As for "just bring an extra pony bottle", you buy it, I'll bring it. I'll even use my own valve, just send the tank. If you don't have an extra one lying around, well, I guess I'll just have to settle for a tiny bit of planning and procedure.
Getting in a second dive is hardly critical. Both I and my usual buddy have called many a dive for reasons from being chilled to feeling slightly "off" to "I have a bad feeling about this". Neither of us would call a second dive just because we had to share air. O-rings blow, stuff happens, and all that is the reason we have a repair and replacement kit with us on the boat. If following our perfectly usual procedures for dealing with problems can preserve redundancy, that's certainly a reasonable pursuit, is it not?
jtivat:
So you are saying the pony is used up and now worthless, fine put the second stage from the pony on your main tank first stage and go diving.
And then if I need the pony, I'll just slap my fins together three times and bubble, "There's no gas like air. There's no gas like air." Then the Mermaid of Oz will show up, wave her magic tubeworm, and cause gills to appear on my neck for the ascent. Unfortunately, I don't believe in Her Deepness, and so, I choose to dive with my own redundant gas supply. To preserve that redundancy in the event of a simple gas failure at depth, when I dive a pony, I dive with an alternate second stage attached to my back gas.
Did you simply not comprehend what I wrote, or did you actively choose to ignore it? If the former, perhaps I should write it out better, as if I was unclear, that is for me to correct. If the latter, there'd be no point to my trying to explain better, but I certainly hope you're not like the "divemaster" helping my instructor with my NAUI MSD class.