Depth averaging tables.

[Eric Sedletzky]

Has anyone here ever depth averaged regular tables?
I'm not talking about the wheel either.
I'm curious if any old school tables divers back in the day ever took something like the PADI RPD or Navy tables to a higher level besides just square profiles?
I know they teach square profiles on the tables, probably because figuring an average becomes very subjective without hard numbers, and so for teaching purposes they had to simplify it, or idiot proof it to some degree, since it was the standard and considering how many people were being trained, etc.

So for an example, say a diver drops from his boat on the edge of a wall to the floor in 130 feet for less than one minute to check his anchor, but then immediately goes up to 50-60 feet to cruise the rest of the wall.
If the diver followed the tables religiously the dive would have to be figured for the deepest depth regardless, so after 10 minutes max (PADI RDP) the diver would be on their way up.
However, if the diver was able to mimic what a computer does they could figure the 130' in as a penalty on the 55' ft average remaining dive and lets say figure the overall depth average as 70 or 80 feet. In other words, pretty much what a computer does.
Who's tried this? What were your results? Did you have any problems, get a hit, get bent?
How did you figure your algorithm/what did you base your theory on?
And what degree or complexity did you take this practice to?
I'm just curious if anybody preempted the computer even before computers were born and had this figured out.

I know this could get very controversial and heated, it seems all table/computer discussion do, but lets look at this from a historical perspective and not something to be considered now.
We have great computers now that do this much better.

 

[tursiops]

No, as far as I know it was not done. You are simply talking a multi-level dive (a while at one depth, a while at another). Although some have used the square-profile tables to do this (by assuming zero SI as they move from one depth to another), the tables are not calculated to allow that assumption. Hence, the Wheel was developed. And the Wheel assumes that each level is at least 20 ft less than the previous level, so the depths are enough different that you actually get some outgassing at the shallower level from N2 you took on at the previous (deeper) level...otherwise you just call it all the same deeper level and ignore the fact that you came up a bit.

It is not really depth averaging.....because time at (say) 40 feet is not half as important to on-gassing as time at 80 ft, thus 60 feet is not a simple linear combination of the 80-ft ongassing and the 40 ft on-gassing. Try it with some tables. Using the RDP, at 40 ft for 40 minutes is PG I. 80 ft for 18 minutes is PG I. If you spent half your time at each depth, say 20 min at 40 ft and 9 mins at 80 ft, then your average depth would be 60 ft for 29 mins, but the RDP give 60 ft for 29 mins as PG K. To stay in PG I at 60 ft your max time would be just 25 mins. Why? Because the greater depths disproportionately put N2 into your tissues.

 

[Eric Sedletzky]

I remember learning the wheel for DM class. As far as I was concerned it was pretty much useless and I knew I would never use it so I can't remember too much about it. I learned enough at the time to pass the exam but that's about it. I don't know if they even require learning the wheel anymore for DM, since I was in it back in 2001-'02
As I remember you could plan three separate depths but then you had to know in advanced the site you were diving so you could plan a wheel dive to calculate how long at what depth. But thet if you were diving an unknown spot for the first time and had no idea what depths you going to be at?
It was also fairly difficult to use as I remember, one digit off and the whole thing was thrown off.

 

[tbone1004]

what tursiops said. The computers don't actually average the depth, they calculate your tissue loading and actively track it, the ongassing happens at different rates at different depths, so if you wanted to compare it to tables, you would be doing something similar to the wheel, but on NAUI/Navy/NOAA tables, it's easier to just do it as a 0 sit interval and do a mandatory 5' precautionary stop as an extra safety buffer. It's not terribly difficult to do, but it's also much better to do your dive plans in software where you can schedule multi-level dives which more accurately mimics what the computers are doing.

 

[Akimbo]

I have never heard of anyone doing it. The only interpolation was moving to a greater depth or time than actual to compensate for factors like workload or cold. We usually wouldn't tell the diver though (surface supplied) since spending more time at a decompression stop was the last thing they wanted to hear when they were cold already.

 

[3D diver]

Nope. Max depth + time=120, when in doubt, round up (in depth, down in time) was what I followed on most dives.

 

[muddiver]

If the table you are using does not have printed instructions that allow multi level or averaging depths, then your diving outside the limits and capabilities of the table. If you get bent you will be paying full-boat for medical assistance. I doubt DAN or your personal medical insurance will cover you if they found out what you are doing. DSAT did some very involved testing and research when they published the PADI tables and then the Wheel. They are used in as pacific manner for a reason and because I am not a hyperbaric Doctor I wouldn't suggest what your proposing let alone know where to start explaining the physics of it.

 

[Eric Sedletzky]

If the table you are using does not have printed instructions that allow multi level or averaging depths, then your diving outside the limits and capabilities of the table. If you get bent you will be paying full-boat for medical assistance. I doubt DAN or your personal medical insurance will cover you if they found out what you are doing. DSAT did some very involved testing and research when they published the PADI tables and then the Wheel. They are used in as pacific manner for a reason and because I am not a hyperbaric Doctor I wouldn't suggest what your proposing let alone know where to start explaining the physics of it.

I'm not proposing anything if you read my post closely, and I'm certainly not going to try it and didn't imply that anybody else should either. I just asked from a historical perspective if anybody ever went off the square profile and cut their own multi level profile on their own, pre computer.

So going back to the 130' drop for less than one minute then an immediate ascent to 50 feet: Would you stay at 50 feet for only 10 minutes then go up if you were on tables to obey the square protocol, or would you stretch the 50' dive out a little figuring you had room since the 130' portion of the dive was so short and there was very little uptake?
And if you did choose to stretch it out, then by how much and how would you base your time limit?... because as I'm seeing it, anything other than a square profile on tables, even a lingered stop at a mid depth would be taking the tables beyond their written rules and would be considered "averaging" the depth and time.
So in essence I would call it "winging it" or "on the fly" at that point.

Correct me if I'm wrong.

 

[tursiops]

So in essence I would call it "winging it" or "on the fly" at that point.

Correct me if I'm wrong.

You are not wrong. You would be winging it, since you are not following your tables. People may have had individual ROE and different degrees of risk tolerance, but all of them are just winging it. Your terms ("depth averaging," "on the fly") sound a lot like ratio deco....another winging it approach.

Depth averaging works great for air consumption...which is linear with depth (pressure). N2 absorption is not. You need to stop using that term. Putting it in quotes is just refusing to admit an error.

 

[lowviz]

I'm not proposing anything if you read my post closely, and I'm certainly not going to try it and didn't imply that anybody else should either. I just asked from a historical perspective if anybody ever went off the square profile and cut their own multi level profile on their own, pre computer. ...//...

Yes, worked rather hard at it. As tursiops said, it isn't linear with depth.

I came up with this for your first hard deco in minutes: divide depth squared (in feet) into 222,222. Compare that to Navy Air Tables.

Cutting to the chase, I came up with something for a multilevel dive that probably wouldn't kill me, but I wouldn't trust it either. The more I learn about deco, the less I know to be true.