I will not teach poor dive planning just because people make bad decisions. I have personal and professional standards which I will not break because people want to justify doing the wrong thing.
I do. the standard is that this is an emergency maneuver for reasons.
a. Both divers need their own independent air source that is attached to them. You are using a tank that is attached to another diver. This is not a safe move for swimming along during your dive. This is taught so that you may safely make it to the surface. It is Not a swimming technique for a buddy pair.
b. You are using your buddy's air as yours. You buddy's great sac rate is a benefit for you in case you have an equipment failure, or you are careless and use up all of your air. It is Not your extra tank.
I teach my students to be thinking divers. They will not entertain this idea, as a result. They understand proper dive planning and why this is a skill to be practiced, not an alternate way to extend their bottom time.
At the end of the day, you will do what you will do. But I will not endorse bad planning.
You are basically saying that gas sharing in a non emergency situaion is unsafe becasue as a diver is swimming and breathing from a tank that is not his or her own. So? If the reg falls out, the diver puts his or her own back in. That is a basic OW skill and no catastrophe is involved. More importantly with a long hose, swimming is very normal with little potential for the reg to get pulled free anyway.
Similarly you are suggesting that that if diver A is good on gas and has lots left, it is just a great big bonus of a reserve. How much do you need? If 500 psi is enough to get each diver to the surface, safely, 1000 psi will get both divers there. So as long as the dive gets thumbed when the reserve needed in either tank is enough to get both divers safely to the surface, there is always complete redundancy. If the receving diver has a failure, they note the bubbles, continu sharing gas and ascend. if the donating diver has a failure, they just switch to the other divers regs and ascend.
Read what Jim said again....
Last summer I was the dive leader for a group from our local dive shop diving the Cayman Agressor for a week.
The captain did an excellent briefing and explained the depth and time profiles. As part of my planning I told three of the newer divers that I was overseeing to be sure and monitor air supplies and let me know when they hit 1,000 psi.
I explained that I dove with a 7' hose and showed them how it was deployed and that the four of us would be diving as a team. Two of the divers were doing fine on their air and 20 minutes into the dive the third diver indicated 1,000 psi. At this point I had about 2300 psi.
We had finished the deep part of the dive and were in about 40 feet of water. I gave this diver my long hose and we dove together for nearly 30 minutes. When I hit 1000 pounds I put him back on his tank and we all began a slow ascent and did our safety stop. We all surfaced with sufficent air. Back on board we debriefed and talked about how we could improve air consumption.
This same situation occurred on the next two days as well with the same outcome. By day three the diver had mastered the basic skills so that he was able to reduce his air usage and finish the dives with the entire group.
This was never an emergency. The diver had enough air at any time to slowly ascend, do a safety stop and surface. We had talked about what we were going to do and why...
In the real world that is how it works with everyone benefitting from increased bottom time, increased comfort and reduced anxiety from the confidence of knowing that sharing gas is really a lot simpler than the catastrophizing attitudes of many instructors would have students believe and that it is something that is within their skill set if the need ever arises for real. I prefer that to semi panicked divers facing a real life air share with only the limited experience of an OW class and a near built in belief and desire that bolting for the surface is an option and or what you do as soon as you mug your buddy for his or her gas.
I have had intentional air sharing to extend bottom time happen in technical diving (both deco procedures and Full Cave) classes where a hoover classmate was directed to go simulated OOA and share gas from me or another class member to ensure that the objectives of the dive could be met while ensuring everyone in the three member team
maintained an adequate reserve for the entire dive.
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To use a flight training example, pilots often practice engine out procedures, simulate forced landings, auto rotations, partial panel approaches, etc, etc, etc, to ensure that when the real deal arrives the responses are automatic and the pilot has the confidence that comes from he or she doing it countless times before. Why would we deny divers the same opportunity to learn and practice skills in the course of a normal dive?
