Posted by Joe R on September 05, 2001 at 22:01:22:
In Reply to: Seems overly complex posted by roakey on September 05, 2001 at 08:49:52:
The point was to show WHY planning is necessary.
Without the explanations taking into account the different cylinder sizes to compensate for the higer SAC a person migh be under the assumption that 1/3 is enough.
I use "method 2" which is basically what you recanted but without the detail of "method 1" the person has no idea why the "rule of thirds" is not being applied.
I feel it is important to show why things are so.. I chose very real numbers.. 3000, and 3100 psi overfils are not uncommon and the two breathing rates are on target for an inshape diver and a larger not in perfect cardiovascular shape.
The sac rates were used to show the total planned dive and that 1/3 would not be sufficient. You plan your dives don't you or do you just do them on the fly??? How do you know if you and your buddy have the gas supply for the intended time... In the case I stated, My dive plan would have been revised and build my bail out tables accordingly.. If we don't have the air for 25 minutes obviously I'm not going to do tables for 35 minutes, I'd now have plans from maybe 10-25 instead of say 15-35 or 40.
If the person is thinking about volume matching, he is obviously thinking about doing a dive that is going to force the team to use 1 entry/exit point where an alternate exit is probably out of the question or very undesirable.
I believe each diver should have a foundation of why things are done not just accept this.. I believe it a good thing for the student to pose questions and scenarios to instructor, if he or she can't answer (or get the answer within reason) it shame on them. Short cuts are good once you understand why they are done..
I teach for several agencies and have a high repeat of my students, They don't mind spending the extra time getting the foundation because in the long run they can make better informed decisions. Granted I wouldn't go into this type of detail on an initial OW student but anyone contemplating techical dives should know what and why they are doing it.