Simpler, OK. But not safer. And what is good if it's not done correctly?
The universal gas plan is to be back on the boat with 500psi. Ok, how do we figure out how to do that? We'll swim around and be back at the up line at around 800psi. Here are two examples where this doesn't work.
- We're doing a 60fsw wall dive. On the NAUI table we have a 55 minute NDL, but decide to be conservative and do 50 minutes. Our plan is to go down the mourning line, swim into the current with the wall on our right for 25 minutes, turn and come back to the mourning. Following guidelines, planning a little and being conservative. The problem is we don't have the gas to do this. At 60fsw with a surface RMV of .7 we are breathing 1.97 cf/min. At 25 minutes we've breathed 49cf, we don't have enough gas to complete the dive. 30 seconds of math on a smart phone calculator solves this. Literally 4 math function - divide by 33, add 1, multiply by your RMV and then multiply by planned dive time.
- Now were diving the U352 at 110fsw, breathing 30%. Using the NAUI tables again with an EAD of 100fsw we stay conservative and decide on a 20 minute dive time. Again the guideline tells us to be back at the up line for our ascent with 800psi. We're diving AL100s so 800psi gives us 24cf of gas. During the dive we are monitoring our air and make our way back to the grapple with 800 psi each. Just as we are getting ready to start our ascent I have a regulator failure and total gas loss. We begin to share air on our way up. The problem is that even without a safety stop we need 26cf to get to the surface and our "guideline" only gave us 24cf.
These are both common dives being executed by OW and AOW divers. I didn't contrive some off the wall scenario to prove a point. Not using basic gas planning leaves gaps. I learned how to gas plan when I was 13, without a calculator or smart phone. This isn't asking too much.