Still sounds like a rather haphazard dive plan.
Haphazard? I guess there's a first time for everything. My mates usually grumble about me being too anal.
You might benefit from a refresher course in reading comprehension, though. I believe I already mentioned that I monitor
both my NDL
and my tank pressure. If that's haphazard, I'd really like to know what makes it haphazard.
Sometimes, when my air consumption is on the high side of normal, I hit
minimum gas pressure before NDL, so it's my gas reserve that makes me go shallower. Sometimes, when my air consumption is on the low side of normal, I get uncomfortably close to the NDL before I hit
min gas pressure, so it's nitrogen saturation that makes me go shallower. The dive is planned on the basis of
both NDL
and expected gas consumption. If that's haphazard, I'd really like to know what makes it haphazard. In fact, I believe that most rec divers don't care about
min gas pressures at various depths, as long as they're back on the boat with 50 bar/725psi (or 500psi, which I understand is the norm on your side of the pond) left in the tank. Which incidentally, is far from enough for a controlled ascent from 20+ meters' depth while donating gas to an OOG buddy, with enough reserves to do a proper safety stop before surfacing.
Now, to reiterate my previous reasoning, in small, bite-sized pieces:
- If your gas consumption is similar to mine, your gas reserves won't allow you a very much longer bottom time on nitrox than on air.
- Sometimes, your gas reserves can limit your bottom time, not your NDL. This depends on tank size and personal gas consumption rate.
- This is a fact no matter whether you plan/follow an air table or a nitrox table (alternatively PDC set to air vs nitrox).
- This means that if you dive nitrox you surface with a lower saturation no matter whether you folllow an air table or a nitrox table.
- Sometimes, your gas reserves allow a somewhat longer bottom time than your air NDL.
- Your gas limited bottom time may still very well be shorter than your nitrox NDL.
- This means that if you dive nitrox you still surface with a lower saturation even if you follow a nitrox table.
- It's only if your gas reserves allow bottom times close to the nitrox NDL that your saturation is just as high on nitrox as it would be on air.
Do you get it now? BTW, there may be other reasons for wanting to surface before your (nitrox) NDL is reached, like a full bladder, or freezing fingers. You can still benefit both ways: Longer bottom time
and reduced nitrogen saturation.