Your Gradient Factors?

[elmo]

This misses the point entirely. We are not talking about the averate bottom depth, but rather the average dive depth.
Simple example using air, calculated on a PADI eRDPML.
100 ft, NDL, 20 mins, but ascend at 15 mins to 40 ft; new NDL is 83 minutes, but stay only 80 minutes. Nice 95-minute dive, plus some ascent time and a SS.
The average depth of that dive is 50 ft ((100x15 + 40x80) /95). A single dive to 50 ft has an NDL of 80 minutes.
You cannot validly plan or execute that two-level dive using average depth.

I do genuinely appreciate it you going to the effort to try this.
You just won yourself one whole hour of extra bottom time because you used an average depth, and you didn't exceed the NDL permitted by the eRDPML.

That is the point I was making. No more. No less. I won't pretend planning based on average depth gives you the optimal answer, but it can give a useful answer. As I said in my earlier post, averaging a shallow-to-deep profile (especially one as extreme as 40ft to 100ft) and planning using "square tables" would not be safe - but we both know the eRDPML won't permit it either.

If I were on a boat with my PADI tables, and my eRDPML (let's pretend I own one) got splashed with seawater and wasn't working, I would happily plan that dive using the tables and average depth.

 

[PfcAJ]

You guys really aren’t going to like what happens if you put 70ft for 45mins into Bühlmann 50/85.

 

[tursiops]

I do genuinely appreciate it you going to the effort to try this.
You just won yourself one whole hour of extra bottom time because you used an average depth, and you didn't exceed the NDL permitted by the eRDPML.

That is the point I was making. No more. No less. I won't pretend planning based on average depth gives you the optimal answer, but it can give a useful answer. As I said in my earlier post, averaging a shallow-to-deep profile (especially one as extreme as 40ft to 100ft) and planning using "square tables" would not be safe - but we both know the eRDPML won't permit it either.

If I were on a boat with my PADI tables, and my eRDPML (let's pretend I own one) got splashed with seawater and wasn't working, I would happily plan that dive using the tables and average depth.

I thought for a long time in this discussion that people were simply moving goal posts. Now I see that they have not even agreed on what the dame is.

I thought the statement that you can use average depth with tables and get effectively the same answer was what was being said, and that such a practice was widespread.
Now you are saying that your point is you get a safe answer, but not the same answer. OK.
But then the other players are not even using average depth of the dive, but rather average depth of the bottom (or the deep segment of the dive) as far as I can tell. Totally different game. Then others are arguing about 4h dives or trimix or saturation or something. Different game, not even the same playing field. And some say well that's what we do locally, which is hardly "widespread."

It certainly appears that the DIR/GUE/UTD guys doing heavy deco have figured out a way to do some sort of (to me arbitrary) averaging that allows them to mostly stay away from DCS. Great.

But folks using the usual tables, from the mainstream agencies, really ought to avoid this "average depth" nonsense. It demonstrably does not work to give the same answer as their max depth and the tables. yes, it may provide a safe answer, although that has not really been shown...just some example where it does work. It would be even safer on a multilevel dive to just use the max depth -- as the tables intended -- and accept that the dive will be shorter than desirable. Or use a multi-level diving tool. Or use a damn computer.

 

[NothingClever]

You guys really aren’t going to like what happens if you put 70ft for 45mins into Bühlmann 50/85.

I get a 1:40 stop at 6m that will probably evaporate before I get there and the 7:00 snooze at 3m is probably just enough time to get into a Rubik’s Cube before I gotta wrap things up.

And I only burn 2700 liters out of 4400 total.

What am I missing?

 

[PfcAJ]

I get a 1:40 stop at 6m that will probably evaporate before I get there and the 7:00 snooze at 3m is probably just enough time to get into a Rubik’s Cube before I gotta wrap things up.

And I only burn 2700 liters out of 4400 total.

What am I missing?

8mins of mandatory deco but the NAUI table says 0.

 

[Storker]

You guys really aren’t going to like what happens if you put 70ft for 45mins into Bühlmann 50/85

Try 30/60.

You can always find an algorithm which is more conservative. The recent discussion was about tables (which generally are rather liberal) and the use of average depth. Quit moving the goalposts, it doesn't become you.

 

[elmo]

I thought for a long time in this discussion that people were simply moving goal posts. Now I see that they have not even agreed on what the dame is.

I thought the statement that you can use average depth with tables and get effectively the same answer was what was being said, and that such a practice was widespread.
Now you are saying that your point is you get a safe answer, but not the same answer. OK.
But then the other players are not even using average depth of the dive, but rather average depth of the bottom (or the deep segment of the dive) as far as I can tell. Totally different game. Then others are arguing about 4h dives or trimix or saturation or something. Different game, not even the same playing field. And some say well that's what we do locally, which is hardly "widespread."

It certainly appears that the DIR/GUE/UTD guys doing heavy deco have figured out a way to do some sort of (to me arbitrary) averaging that allows them to mostly stay away from DCS. Great.

But folks using the usual tables, from the mainstream agencies, really ought to avoid this "average depth" nonsense. It demonstrably does not work to give the same answer as their max depth and the tables. yes, it may provide a safe answer, although that has not really been shown...just some example where it does work. It would be even safer on a multilevel dive to just use the max depth -- as the tables intended -- and accept that the dive will be shorter than desirable. Or use a multi-level diving tool. Or use a damn computer.

Your earlier post complained that all the examples of using average depth were beyond the scope of recreational diving performed by the majority of divers. I gave you an example that was within "recreational limits", and independent of any agency.

You mean I need to include DIR/GUE/UTD as part of the broader world of recreational diving? Naw. They are outliers, a tiny fraction of the global diving activity.

My view of tables and actual depth comes from pre-computer days diving in Chicago, New England, Europe, using many kinds of tables. ALL of which clearly specify actual depth, not some sort of average depth.

One example above talked about going between 220 ft and 240 ft and calling it 230 ft. OK, that is what is called a tangent linear approximation, perfectly plausible for gas up take. But that is not the average depth of the dive, just of a little segment of it. That appears to be what the Ratio Deco folks have reinvented, the tangent-linear approximation. No magic, but definitely not the average depth of a dive, just of some segment of the dive.

The examples above that are trying to justify their position are really way off in the corner of recreational diving: trimix, 240 ft, 4h dives, O2 switch and deco, etc. Does the Navy dive manual or the NOAA diving manual or DCIEM or BSAC or anybody in the mainstream use average depth with a table?

 

[PfcAJ]

Try 30/60.

You can always find an algorithm which is more conservative. The recent discussion was about tables (which generally are rather liberal) and the use of average depth. Quit moving the goalposts, it doesn't become you.

None of this is precise enough to be concerned with goalposts.

certainly not precise enough to be overly concerned over 6ft.

 

[scubadada]

You guys really aren’t going to like what happens if you put 70ft for 45mins into Bühlmann 50/85.

8mins of mandatory deco but the NAUI table says 0.

Hi @PfcAJ

What was your example of 70 ft for 45 min used to illustrate? You did happen to choose a depth where the NAUI table appears to have an outlier long NDL, nearly as long as USN and considerably longer than PADI. It would correspond to a Buhlmann GF high well in excess of 99. You could just as easily chosen 60 ft. Here the NDL is in line with the PADI NDL and would correspond to a Buhlmann GF high of somewhere just above 99. Why did you compare to a GF high of 85?

 

[PfcAJ]

Hi @PfcAJ

What was your example of 70 ft for 45 min used to illustrate? You did happen to choose a depth where the NAUI table appears to have an outlier long NDL, nearly as long as USN and considerably longer than PADI. It would correspond to a Buhlmann GF high well in excess of 99. You could just as easily chosen 60 ft. Here the NDL is in line with the PADI NDL and would correspond to a Buhlmann GF high of somewhere just above 99. Why did you compare to a GF high of 85?

View attachment 626354

Simply highlighting that none of this stuff is exact.

And as such, avg depth works pretty darn well.