Pressure group question

[**pYgmY**]

Hi all,

I have a theory question about calculating the post-dive pressure group for a specific dive profile: max. depth = 28.5m, bottom time = 45min, descending to max. depth at the beginning of the dive and then slowly but steadily ascending to the surface (along a shipwreck), including a 3min safety stop at 5m.

As far as I understand it, the times and pressure groups shown on PADI dive tables always assume a square dive profile. This dive would be multi-leveled, but really is more like a slow ascent from max. depth.. How can I calculate the correct post-dive pressure group for a profile like this? And if there is a way, could someone with more experience help me out by providing the correct result (so I know where to continue in the PADI tables for a repetitive dive calculation)?

Thanks!

 

[L13]

OK, here's the challenge. Air dive to 120 ft. Compare square profile table, stair-step multi-level, Ratio Deco, whatever else...How much time-in water (including Safety stop) do you get for a non-deco dive?
...
Your turn.

Easy:
SubSurface(or any other system): 120' for 1 min. Ascend to 20'. Switch to a hookah system and stay there till you are bored, NDL for ever.

Your challenge was insufficiently defined.

 

[arew+4]

"Basic" forum, put the ruler away.

 

[steinbil]

The simple answer is that the tables are made for square profiles, and you can't use depth averaging. Also, computers are more efficient at maximizing bottom time.

Thank you for your quick responses! I'm aware that in reality most dives are multi-leveled and that dive computers can calculate more complex profiles automatically. I was just wondering if there is a "manual" method that can be used for profiles like this that I'm not aware of. Thanks for clarifying

The more complicated answer is that it is possible with certain caveats. Some think this is too advanced for the basic forum, so I won't go into details, but you can read about it in the book "Beginning with the End in Mind - Fundamentals of Recreational Diving", or you can make a thread in the advanced forum. In any case, you should probably just stick to your training.

 

[scubaozy]

The suggested method is not valid. Do not attempt to use a square-profile table for a multi-level dive.

Have you actually tried and compared with wheel. I do not have the wheel handy it would be interesting to see how it compares. If someone has both, could you please post what group you get with both using same multilevel profile?
Never mind just realised there are older threads