The OP might get something from an article I recently wrote for SDI.
Gas Management Techniques for Sport Divers | tdisdi.com
Pony setup: Octopus or not ?
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The OP might get something from an article I recently wrote for SDI.
Gas Management Techniques for Sport Divers | tdisdi.com
dumpsterDiver
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Randy43068
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Find the answer to why you carry the pony bottle.
Funny, but I've found the opposite... given a couple of qualifications.
1) deeper than 30 metres
2) desire to do a safety stop of at least three and possibly five minutes
When I worked on the solo manual for SDI we did calculations for gas needs on a dive to 30 metres, hence the recommendations that around 380 - 400 litres/13-15 cubic feet of gas is the recommended MINIMUM. This is based on an average SAC influenced by heavy workload and stress. Deeper and the requirement increases of course.
In addition, a 40 is reasonably easy to manage in water once the punter is taught how to rig it. My experience is that a 40 is actually neater than a 30 while a 15 cubic foot cylinder is the most tricky of all... since it is too small to rig as a stage/sling, and I am not a fan of bailout cylinders rigged on main tanks.
dumpsterDiver
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So in your experience more people sling 40 cu-ft pony bottles than smaller ones??
Or are you talking about just the small segment of the divers who feel compelled to have enough redundant gas to spend 5 mintes at 20 feet for an OPTIONAL stop during a true emergency?
40 cu-ft pony bottles are not common where I dive.
Yep. Maybe a function of the area and the prevalence of quasi-techies here or the diver population with whom I have regular contact... but yes, I would say that 40s are more popular here by an order of magnitude.
Not sure what you mean. Primarily, one can make a good argument that once a dive has been conducted below 30 metres, a stop is less optional more "Best Practice" if not actually required. A gas emergency does not make any "decompression obligation" or "Best Practice" dissolve, therefore having sufficient gas to meet those needs -- emergency or not -- seems like good contingency planning.
Of course one could make an argument that in an emergency, a diver should shoot to the surface and get outta the water... but that kind of goes against everything I teach and write about.
If a diver becomes too freaked out by -- let's say a freeflow -- that she is unable to deploy her backup and execute a normal controlled ascent, she needs remedial training and does not belong below 30 metres... in my considered opinion, but others feel differently. By the same token, I believe that a dive below 30 metres requires the diver to carry a redundant gas source and regulator... again, your mileage may vary.
Which is why I write articles... teaching is about modifying behavior. In this case, my belief is that a having enough gas to ascend properly and the skillset to use that gas in a fashion that's prescribed by best practice, is the goal.
Life is not black and white, and frankly, any amount of back-up gas is better than none... but if someone is going to the bother of carrying a redundant gas source, why not make sure it is going to function in the most extreme circumstances on a pinnacle dive for the diver.
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funny, back a bit ago, I got "flamed" for asking if carrying EAN28 in a pony vs. air would be a "favorable" method. Nobody agreed...... called it "gas switching" and "dangerous". I thought of it because of (1) recreational and hard bottom limits here, and (2) allowed for a cushion vs. air on the NDL "clock".
If I needed gas, I'd gladly use you EAN28 (or air)... LOL
The debate over the flavor of gas to use is an interesting one. On a public forum without the "due diligence" stating that one has to have so-and-so certification, AIR is the default. FYI, I usually only put air in my CCR diluent bottle (occasionally) and my bike tires but what I do is beside the point.
At issue always in these issues is: what is practical, what is best practice, what's the norm with the folks you dive with, what raises the bar a little, what you feel you are capable of managing.
Crush
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Back to the original question.
I occasionally dive with a pony bottle. For more details on my setup - how and why, click here: http://www.scubaboard.com/forums/tanks-valves-bands/372271-pony-redundant-set-up-2.html#post5761909
To directly address your question, I believe that there is great benefit in standardization. That way, when I practice any of my skills, my actions are the same, all the time. This helps to eliminate stress-induced errors. For that reason I always have my primary reg and my octo on my main tank - if you are OOA I will always donate my primary reg (long hose) and begin to breathe off my octo. Also, my pony bottle is slung in front of me so that I can clearly see the pony, its pressure gauge, and the regulator on the pony - unlike back-mounted systems I can easily hand off this pony with no risk of entangling hoses and I cannot mistakenly begin to breathe off my pony (thinking that it is my main tank) while monitoring my main tank pressure.
Safe diving!
-Crush
I occasionally dive with a pony bottle. For more details on my setup - how and why, click here: http://www.scubaboard.com/forums/tanks-valves-bands/372271-pony-redundant-set-up-2.html#post5761909
To directly address your question, I believe that there is great benefit in standardization. That way, when I practice any of my skills, my actions are the same, all the time. This helps to eliminate stress-induced errors. For that reason I always have my primary reg and my octo on my main tank - if you are OOA I will always donate my primary reg (long hose) and begin to breathe off my octo. Also, my pony bottle is slung in front of me so that I can clearly see the pony, its pressure gauge, and the regulator on the pony - unlike back-mounted systems I can easily hand off this pony with no risk of entangling hoses and I cannot mistakenly begin to breathe off my pony (thinking that it is my main tank) while monitoring my main tank pressure.
Safe diving!
-Crush
Hum, the discussion here has been varying, and not always answering the question.
As I understood it, the OP wanted to know if there was any disadvantage in removing their octo from their primary reg when they dive with a pony.
I see this as two separate points.
The octo is to provide your buddy with air in case his air supply is no longer there (s/he is OOA, has first stage failure, whatever..). You are then two diving off the same air supply. There is no reason for YOU to use your octo, except perhaps if you have a second stage failure AND you have an isolator valve between the first and (failed) second stage. You have a first stage failure or are OOA, then an octo is no use.
The pony is to provide YOU with an completely independent air source when your primary air supply is no longer there (You are OOA, you have had a first stage failure, whatever..). Your buddy can use it if necessary.
So, based on this, yes you can remove the octo. If you do this, you have to know that there is no way for the person breathing from the pony to know the pressure in the tank.... unless you have an SPG on the pony as well.
However, as a practical consideration, It would depend on how often you dived with the pony. If it is every dive, then removing the octo permanently is valid. If you only dive occasionally with the pony then I would leave the octo there. Then you have to find what works for you in terms of hose routing, and where you stow the second stages. I would however tend towards always diving with the same setup, so would have the pony on each dive, and set the regs up like this as well.
As an tangential comment, the French have a similar analysis. They tend to dive with a Y valve on their tank, and two first stages, with one second stage on each. With a drysuit and BCD I have one inflator from each first stage. I lose a first stage? still have air for me and buoyancy control. Regular practice at switching off one of the first stages is however necessary. There is quite a lot of logic in this setup. It is very similar in redundancy to the above tank + pony setup.
Jon
As I understood it, the OP wanted to know if there was any disadvantage in removing their octo from their primary reg when they dive with a pony.
I see this as two separate points.
The octo is to provide your buddy with air in case his air supply is no longer there (s/he is OOA, has first stage failure, whatever..). You are then two diving off the same air supply. There is no reason for YOU to use your octo, except perhaps if you have a second stage failure AND you have an isolator valve between the first and (failed) second stage. You have a first stage failure or are OOA, then an octo is no use.
The pony is to provide YOU with an completely independent air source when your primary air supply is no longer there (You are OOA, you have had a first stage failure, whatever..). Your buddy can use it if necessary.
So, based on this, yes you can remove the octo. If you do this, you have to know that there is no way for the person breathing from the pony to know the pressure in the tank.... unless you have an SPG on the pony as well.
However, as a practical consideration, It would depend on how often you dived with the pony. If it is every dive, then removing the octo permanently is valid. If you only dive occasionally with the pony then I would leave the octo there. Then you have to find what works for you in terms of hose routing, and where you stow the second stages. I would however tend towards always diving with the same setup, so would have the pony on each dive, and set the regs up like this as well.
As an tangential comment, the French have a similar analysis. They tend to dive with a Y valve on their tank, and two first stages, with one second stage on each. With a drysuit and BCD I have one inflator from each first stage. I lose a first stage? still have air for me and buoyancy control. Regular practice at switching off one of the first stages is however necessary. There is quite a lot of logic in this setup. It is very similar in redundancy to the above tank + pony setup.
Jon
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