OP
lefrogster
Registered
Just curious, How many dives did it take to complete your Deco class?
I did the standard PADI course, which I remember was 1 confined, 3 open water dives and a check out dive. I don't have any issues with buoyancy or meeting the run time, but I don't see sticking to the run time to be THE most important thing in deco: better to ensure the you're breathing the correct gas at the correct depth. I also have an issue with the NOTOX procedure, where you're basically doing the first steps of the switches on your own (perhaps while ascending to the next stop) and then checking your partner, only AFTER the switch (which might be too late for him if he switched to the wrong gas).
When I moved over to IANTD, basically, you do the switches sequentially, not simultaneously, which allows your partner to check your gas and depth with you and watch you while you do the switch. It takes longer, but I feel is more secure and certain. Only after you both have successfully switched do you start the deco time, so its a time relative to when you complete the switch (not an absolute time).
Most of the time this just follows the run time, but if there is an issue -- free flow, entanglement, down current, problem with bottle rotation, problem with DPV -- you spend time to fix that problem first before starting your deco count. Else you risk ascending to the next stop before the problem is fixed. If you overrun the run time, you then have to recalculate your remaining stops by adding x minutes to each of them, which can further cause error.
---------- Post added February 28th, 2014 at 02:26 PM ----------
hey everyone, thanks for the valuable input. I just want to clarify that I'm not advocating diving without a plan. Its diving with a relative run time for deco rather than an absolute one.
For instance, in my PADI instruction, if we spent 30 min bottom time, 1 min to reach first deco stop at 21 m and 2 min per stop for the 50%, our plan would be something like:
- 21 m at 31 min switch to 50%
- 18 m at 33 min
- 15 m at 35 min
- 12 m at 37 min
... etc.
Let's say someone takes longer getting to 21 m for whatever reason and is 30s late. Then you have to pad the remaining times by 30s in your head. Then if at 6m switch, there is another delay, you have to pad that time and the 30s to your original run time.
At IANTD, we would just start the count at 21 m only after everyone has switched regardless any delays. It would be:
- 21 m at 0 min switch to 50%
- 18 m at 2 min
- 15 m at 4 min
- 12 m at 6 min
So you're just starting the count T0 at the moment of the deco switch and abandoning the absolute run time of the dive itself.