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Well...
Some European tables officially use avg depths of the dive.
Comex comes to my mimd.
They are freely available as its use has even been published as legal requirements for people using them under professional activities.
And yes, like USN or other pro tables, they are/were used by rec divers under the name of "tables MT 92".
Will try to post a pic of a submersible table later.
Thank you for this, but I see nothing on that table (or on others I found using MT92 to search, thank you for the link) that says depth is the average depth of the dive.. In fact, the air version of the table I found (MN90) has times similar to the old US Navy tables for air.

Perhaps you mean the average depth of the bottom?
 
Thank you for this, but I see nothing on that table (or on others I found using MT92 to search, thank you for the link) that says depth is the average depth of the dive.. In fact, the air version of the table I found (MN90) has times similar to the old US Navy tables for air.
Perhaps you mean the average depth of the bottom?
If you look at the pic of the table I posted, you take a Temps (time) 1 and a Profondeur (depth) 1 and get a Coefficient (value) 1.
You do the same for T2 and P2
Then you add T1 and T2 to get the T and C1 + C2 to get C
You take this T (total dive time) in the upper line, go down till you get the C value and it gives you the Profondeur Similaire (equivalent depth)
10min at 27M =>27
30min at 18m =>54
so 40min for C= 81
go to 40min down to 84 (no 81, so you take the next) and you get PS at 21
so your dive is like a 40min at 21M
 
If you look at the pic of the table I posted, you take a Temps (time) 1 and a Profondeur (depth) 1 and get a Coefficient (value) 1.
You do the same for T2 and P2
Then you add T1 and T2 to get the T and C1 + C2 to get C
You take this T (total dive time) in the upper line, go down till you get the C value and it gives you the Profondeur Similaire (equivalent depth)
10min at 27M =>27
30min at 18m =>54
so 40min for C= 81
go to 40min down to 84 (no 81, so you take the next) and you get PS at 21
so your dive is like a 40min at 21M
OK, got it. Now what do you do with that information?
If I do the same thing with the Navy tables I get Group C for the first segment, and Group F for the second segment, and Group H for the "average" segment. What actually is my nitrogen status if I use that 40min at 21m information? Don't I have to take into account the residual nitrogen from the first segment?
I understand depth averaging; that is what your table helps me with. But the issue is nitrogen averaging.....
 
@tursiops , I can't find the post right now, but IIRC you claimed that tables couldn't be used for multilevel dives.

A little time ago, you yourself posted a link to a method for planning multilevel dives using only the PADI RDP table. I've been using that method for much of my diving career since most of my dives are multilevel or triangular profile. Granted, you have to do some simplifications, but IME it works pretty well. At least for planning.

I've looked a bit more into that method, and it seems that what it does is basically treating a multilevel dive as a series of square dives with zero SI. It has its limitations, but not more than that I routinely use it for my dive planning. With pretty good results.
 
@tursiops , I can't find the post right now, but IIRC you claimed that tables couldn't be used for multilevel dives.

A little time ago, you yourself posted a link to a method for planning multilevel dives using only the PADI RDP table. I've been using that method for much of my diving career since most of my dives are multilevel or triangular profile. Granted, you have to do some simplifications, but IME it works pretty well. At least for planning.

I've looked a bit more into that method, and it seems that what it does is basically treating a multilevel dive as a series of square dives with zero SI. It has its limitations, but not more than that I routinely use it for my dive planning. With pretty good results.
Sorry to be confusing about this.
Tables cannot be used for multilevel dives unless you modify something.

The trick of assuming zero SI as you move up from one level to the next shallower is OK, but you still have to have a way to take into account the nitrogen you did not off-gas because you did not spend the time (and decreased ambient pressure) to go all the way to the surface. That is what the attached article takes into account, and what the Wheel and eRDPML do.

There are some levels and times at each where the nitrogen differences get lost in the coarseness of the tables quantizing. But you cannot tell in advance which depths/times these are, so the rules of the attached article take that into account to help you:
upload_2020-11-25_11-5-25.png

What is clear is that you do NOT get the same nitrogen status after a multilevel dive using these correct methods as you would if you use a time-depth averaged "equivalent depth" (as Jale called it) for the total time of the dive. In fact, you may not even be able to execute the dive without exceeding NDL by using an equivalent depth, namely the average depth of the DIVE (not of the BOTTOM). Worse, you do not know if you exceeded NDL because there may be nothing in the dive calculation to tell you. An example, using the air eRDPML because it is easy to use:
30m for 18 mins (NDL is 20 min); PG is M
10m for 100 mins (reduced NDL is 130 mins); PG is now X. (SS required)

Average ("equivalent") depth is 13m.
13m for 118 min (NDL is 98 min). I can't do this dive without exceeding NDL.

If the second segment of my dive were just 80 min instead of 100 mins, the calculation would go like this:
30m for 18 mins (NDL is 20 min); PG is M
10m for 80 mins (reduced NDL is 130 mins); PG is now W. (SS required)

Average ("equivalent") depth is 14m.
14m for 98 min (NDL is 98 min). PG is now Y. (SS required)
So this dive is possible, but my ending pressure group is TWO groups higher than the actual multi-level calculation.
Consequences: longer SI than actually needed, or else less surface of-gassing than expected if this is not taken into account.

Summary: the table are not designed for use with any kind of depth-averaged dive profile, but you can concoct situations where is can still work. But is is not clear what these situations are without actually doing the multio-level dive calc, in which case you did not need to do the depth averaging.

One additional comment:
by "average depth" some folks clearly mean the average depth OF THE BOTTOM, not the average depth of the dive. Those are very different numbers, calculated differently.​
 

Attachments

  • RDP for Multi-Level Dives_AAUS1991_3.pdf
    5 MB · Views: 119
you still have to have a way to take into account the nitrogen you did not off-gas because you did not spend the time (and decreased ambient pressure) to go all the way to the surface. That is what the attached article takes into account, and what the Wheel and eRDPML do.
So... Why do I see no difference at all between following that method and using an electronic planner with multiple dives with 0 SI?

If I don't see a difference, you'll have a hard time convincing me there is a (practical) difference.
 
So... Why do I see no difference at all between following that method and using an electronic planner with multiple dives with 0 SI?

If I don't see a difference, you'll have a hard time convincing me there is a (practical) difference.
Try it with the example I gave.
 
An example, using the air eRDPML because it is easy to use:
30m for 18 mins (NDL is 20 min); PG is M
10m for 100 mins (reduced NDL is 130 mins); PG is now X.
Using the method in the paper and the metric PADI RDP table, I get:
18 min@30m = PG M
Add 100min @10m = PG X

Using the Android Dive Planner app (which basically is the PADI RDP on a cell phone platform) I get:
1st dive: 18 min@30m = PG M.
Zero SI
2nd dive: 100 min @10m = PG W

Within rounding errors, that's good enough for government work. At least for me.
 
To be honest, with regard to my personal diving, I am watching the current debate over maximum depth v. average depth for use on tables on recreational dives with the same fascination I would have for a current debate on Betamax v. VHS.
 
One additional comment:
by "average depth" some folks clearly mean the average depth OF THE BOTTOM, not the average depth of the dive. Those are very different numbers, calculated differently.​

Where average depth can come in really handy in the deco profile is for example, a long shallow scooter dive or long shallow swim out to a dive site and then dropping down to a site.
 
http://cavediveflorida.com/Rum_House.htm

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