Reverse dive profile advice

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But the point is his only planning tools appear to be tables that he apparently doesn't have or perhaps even know how to use....so the only safe assumption for him is a square profile, so the only safe answer for him is to shorten the second dive. If he uses the PADI RDP, the first dive (50 ft) puts him in PG O, which after a 75 min SI is PG E. That's 13 mins of RNT at 75 (80) ft, so his remaining BT is just 13 mins. He could do a 13 min dive, but not a 45 min dive.
If he has a computer, the game changes....but only a little. Even if his first dive (being multi-level plus a 75 min SI) gives him zero residual nitrogen, he still can't go to 75 ft for 45 mins on the second dive. His second dive must also be multilevel, and most likely aslo considerably less than 45 mins.

The only safe answer is no answer so he can't blame you after he screws the pooch.
 
Not to be captain obvious here, but why not get your nitrox certification?

He seems to have his hands full with 21% presently. Task overloading isn't indicated.
 
OP, if you are still around, just get yourself a basic, nitrox capable computer. If you do not use a computer you are just cheating yourself. While some old timers can compute from a table on the fly it is really archaic. There is nothing wrong with a reverse profile as you have offered. Just stay on the conservative side and a decent surface interval and you will be fine. A safety stop is a non-required stop that has some how become mandatory. It should not be thought of as a required deco stop. If you need a deco stop then you are in deco and diving well outside of a Basic SCUBA certification. Make it easy, get a computer, if you already have one, then use it conservatively. In some cases, you can nearly double your dive time over conventional use of a printed table. There are several people I dive with often enough, including my wife and myself and several others, who make the Cozumel dive guides cry uncle and laughingly order us out of the water well after an hour with max depths approaching 100 feet but we spent the majority of the dive up shallow looking for critters in the grass shallows. If we were strictly using the tables we would be back on the dive boat and our poor guides would be much happier. Have fun, be safely dangerous. N
 
25 minutes at 50 feet (total dive time 27 minutes) gives me an 18 minute penalty. Playing on the beach for 70 minutes will give me 5 minutes credit.
80 feet for 20 minutes plus my 13 minute penalty will get me out of the water without a stop.
 
25 minutes at 50 feet (total dive time 27 minutes) gives me an 18 minute penalty. Playing on the beach for 70 minutes will give me 5 minutes credit.
80 feet for 20 minutes plus my 13 minute penalty will get me out of the water without a stop.

Resting on the beach, physical activity during an SI is thought to be problematic for off gassing
 
You’re asking us?! Just looking at it it seems like a reasonable day of diving, but I certainly wouldn’t trust that with my health. What does your computer (or old school tables) have to say? You do have one and know how to use it... right?

The safety stop is a safety stop, not a deco ceiling.
your old school tables say these algorithms were developed with the assumption that the deepest dive is done first and all subsquent dives are the same depth or more shallow. You're literally diving into uncharted territory.
 
your old school tables say these algorithms were developed with the assumption that the deepest dive is done first and all subsquent dives are the same depth or more shallow. You're literally diving into uncharted territory.

It's done quite often actually. Last time for me was wreck diving off NC. The weather off shore kept us in shore for the 1st dive, later the winds changed and we did the 2nd dive off shore at depths 2x the 1st dive. My PDC or any of the other 19 diver's PDC didn't have a problem with it, it happen 2 days that week.

IMO if the OP needs advice on this very basic issue the OP needs to go "back to the drawing board".
 
your old school tables say these algorithms were developed with the assumption that the deepest dive is done first and all subsquent dives are the same depth or more shallow. You're literally diving into uncharted territory.

This is correct. Tables != computers.
 

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