Depth averaging tables.

[Basking Ridge Diver]

Yes, you can do this on any set of tables. But you do not get an answer that you should use, unless you are very far away from any limits. That is why the Wheel was invented.
This paper explains how to validly use the RDP with multilevel dives. The same ideas will apply to all tables, but there is no way to test them because there is no equivalent to the Wheel for those other tables. Sorry, I cannot attach the paper (too large), but you can get it on Rubicon with this link.

I finally had the time to read it -

And after I ran some of their examples with the tables - each example was done with the tables and all within NDLs and match their results.

Page 25 was the most telling see below -

Differences between the table method and the wheel
Although these rules seem simple enough, perhaps even simpler than the Wheel's, there are inevitably tradeoffs when using a simpler instrument. A few of the most salient benefits of each method are summarized below. This list is not intended to be complete, merely indicative of the major tradeoffs between the methods.

Advantages of the table method:
- As an extension to familiar table-based planning methods, the method presented appears easier to learn, use, and remember than the Wheel.
- Table method is not subject to device calibration errors.
- Results are more repeatable. This is no uncertainty in eye-table alignment through three layers of plastic, an no possibility of inaccurate arrow alignment.

Advantages of the wheel:
- Requires no calculation of repetitive nitrogen time, thereby eliminating Table III.
- Requires no arithmetic save when calculating time intervals.
- Allows slightly more bottom time.
- Allows 5ft depth increments rather than 10 ft increments, allowing more bottom time if instruments and profile allow sufficiently accurate planning and execution.

So how is it after reading this article you believe tables can not be used in multi level diving?

 

[NAM001]

I have never done this because I use computers but if I had to using your example I would say that at 130 you have 8 min for ndl. You being there 1 minute you have uses 12% of your ndl. I would then move up the table to 60 ft see I have 60 minutes and then inflate the 12% to 20% and enter the 60' portion of the table with 20% of the time already used 20% of 60=12 the nearest time is 15 in on the table I have so I would consider that 15 minutes have been used and continue the dive.

 

[Basking Ridge Diver]

I have never done this because I use computers but if I had to using your example I would say that at 130 you have 8 min for ndl. You being there 1 minute you have uses 12% of your ndl. I would then move up the table to 60 ft see I have 60 minutes and then inflate the 12% to 20% and enter the 60' portion of the table with 20% of the time already used 20% of 60=12 the nearest time is 15 in on the table I have so I would consider that 15 minutes have been used and continue the dive.

There is no guessing when you use the tables - you use the tables as they taught you - except you use 0 or 10 min for a SIT time.

One of the examples they used was -
110 feet for 16 mins - 70 feet for 8 mins - 50 feet for 14 mins

So using the Naui tables -
110 for 16 mins puts you at letter G after your first segment (5 min deco incurred)
with a 10 min SIT
70 feet for 8 mins puts you at letter I after your second segment (cleared of deco)
with a 10 min SIT
50 feet for 14 mins puts you at letter L after your third segment (5 min deco incurred)

There is no guessing or taking percentages... it is table driven so you just follow your tables.

They do give you three guidelines -
1) Only the first depth is allowed to be greater than 80 feet and to the full table NDLs.
2) Repetitive depths are limited depending on the previous depth.
3) Repetitive depth NDLs are reduced for the second and third depths.

A better profile would be -
110 feet for 13 mins ending letter E
70 feet for 12 mins ending letter H
50 feet for 13 mins ending letter J
All within NDLs - no Deco incurred

 

[tursiops]

So how is it after reading this article you believe tables can not be used in multi level diving?

There is no point in arguing with me because I agree with you.....tables can be used for multilevel dives if they are used according to rules that allow them to match the Wheel.

What i object to is using the tables for a multilevel dive without using the special rules. An example of incorrect use is 100 ft for 10 minutes, 90 feet for 5 minutes, 70 feet for 10 minutes, 60 feet for 3 minutes, 50 feet for 10 minutes, 40 feet for 10 minutes. People try to use tables for this by figuring out the Pressure Group after 10 minutes at 100 ft, then looking at 90 feet for 5 mins as a repetitive dive with zero SI, getting a new PG, etc. The incorrect principle is to assume a zero SI to move to the net level up, and just retaining PGs. What is worng with this example is several things: there are too many levels to fit the rules; the depth intervals are only 10 feet instead of 20 (which releases enough pressure to allows useful offgassing); and no credit is given for the ascent time. When the tables were constructed, part of the calculation is the offgassing that occurs during ascent; this gets taken into account incorrectly when the tables are used to "calculate" at multilevel dive, hence the Wheel, which knows how to do it, or the paper you read which duplicates the Wheel rules.

If you arbitrarily use tables to calculate a multi-level dive, you might luck out and not run afoul of any of the issues involved. Your best chance to not run afoul is to not go too deep, don't do too many levels, have the levels at least 20 feet apart, and stay away from the NDLs. If you do this, in fact you'll be following the rules in the paper you read....and duplicating what the Wheel does.

I use my computer, of course.

 

[NAM001]

That's all well and good but your examples is not what the OP presented. he presented 1 min at 130 and the rest of the time at 50-60. A nauii table does not have a 1 min column only a 5 and that is >50% f your ndl. The tables will not give any where near an accurate result with the dive presented by the OP. Once you get to 5 minutes the story changes and the tables will function. 1 min at 130 does not do much to a 5 min compartment. Dives like that is why a computer is so much better. Never the less if you do go to a depth and leave it at a given group you can move with in the depths as long as you stay in the group. It may not be proper but it dies seem to work. Skipping any SI will only provide additional margin for error. The nauii table I looked at did not have a 0 SIT It did have a 10 but the results are still the same.

There is no guessing when you use the tables - you use the tables as they taught you - except you use 0 or 10 min for a SIT time.

One of the examples they used was -
110 feet for 16 mins - 70 feet for 8 mins - 50 feet for 14 mins

So using the Naui tables -
110 for 16 mins puts you at letter G after your first segment (5 min deco incurred)
with a 10 min SIT
70 feet for 8 mins puts you at letter I after your second segment (cleared of deco)
with a 10 min SIT
50 feet for 14 mins puts you at letter L after your third segment (5 min deco incurred)

There is no guessing or taking percentages... it is table driven so you just follow your tables.

They do give you three guidelines -
1) Only the first depth is allowed to be greater than 80 feet and to the full table NDLs.
2) Repetitive depths are limited depending on the previous depth.
3) Repetitive depth NDLs are reduced for the second and third depths.

A better profile would be -
110 feet for 13 mins ending letter E
70 feet for 12 mins ending letter H
50 feet for 13 mins ending letter J
All within NDLs - no Deco incurred

 

[Storker]

OK, KWS, let's go back to the example in the OP and use the method presented in the paper tursiops linked to. The article uses the PADI table, so that's the one I'll use as well. Besides, I don't have the NAUI table available.

The shortest time at 130' in the imperial unit PADI table is 3min. We'll use that number. At 60' that would be a 6 minute "penalty". So instead of an NDL of 55 minutes at 60', the max total run time allowed after the bounce to 130' would be 55-6=49 minutes.

I'm on metric units, so let's do it on the metric RDP. 130' is approximately 40m, 50-60' is 15-18m. I'll use 18m. On the metric table, the shortest time at 40m is 5 minutes, so I'll use that. That gives me a "penalty" of 11 minutes at 18m. So instead of an NDL of 56 minutes at 18m, the max total run time allowed after the bounce to 40m would be 56-11=45 minutes.

If I do this on Suunto Dive Planner 1.0.0.3, the numbers it gives me line up pretty well with the table approach. The minimum segment the program allows for is three minutes, so I enter 3 minutes at 40m, then an ascent to 18m. This simulation puts me in deco at 50 minutes runtime.

The multilevel table approach looks pretty good to me. And I did that plan on the RDP in less time than it would take me to turn on my computer and push the buttons required to get it into planning mode...

 

[Diver0001]

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.

This is pretty much what Ratio deco does and to a certain extent is also how a computer works. In the late 80's a couple of the divers in the little clique I dove with used to do this with tables on certain dives but they used it for calculating surface intervals as opposed to NDL's. As far as I know they never got bent but there's a lot of slack in the tables so maybe that's the reason. Manually keeping accurate track of average depth on the fly is a PITA. I would recommend a computer if you want to make multi level dives.

R..

 

[Basking Ridge Diver]

There is no point in arguing with me because I agree with you....
I use my computer, of course.

Misunderstood your point before - I thought you were saying the tables are dangerous and should not be used.
And I agree on any deep dives a computer is the correct tool - that said I often check my tables for multilevel diving before I go.

 

[DA Aquamaster]

That's all well and good but your examples is not what the OP presented. he presented 1 min at 130 and the rest of the time at 50-60. A nauii table does not have a 1 min column only a 5 and that is >50% f your ndl. The tables will not give any where near an accurate result with the dive presented by the OP. Once you get to 5 minutes the story changes and the tables will function. 1 min at 130 does not do much to a 5 min compartment. Dives like that is why a computer is so much better. Never the less if you do go to a depth and leave it at a given group you can move with in the depths as long as you stay in the group. It may not be proper but it dies seem to work. Skipping any SI will only provide additional margin for error. The nauii table I looked at did not have a 0 SIT It did have a 10 but the results are still the same.

It's not a realistic schedule. To get 1 minute at 130 ft, you'd have to descend at slightly greater than 130 fpm, then immediately begin your ascent to the next level. Run times start upon leaving the surface.

Realistically, you'd need a couple minutes to descend and some fraction of a minute to initiate your ascent. Rounding up then, you've incurred 3 minutes of bottom time to apparently just to go to 130' to say you've done it.

A 130' depth for anything up to and including 3 minutes will result in "Group A" on the wheel so it really doesn't matter if you do it any faster than that anyway. 4 minutes will be "Group B" and 5 minutes will be Group C, and anything longer than that goes up about 1 group a minute - just like it does on the PADI RDP.

----

As indicated above the major differences between the Wheel and the RDP are the five foot depth intervals, shorter MLs, and the specific rules that must be applied:

1. you can only use the NDL on the first (deepest) leg, and you must use the MLs after that;
2. the second leg of a multi-level dive cannot be deeper than 80 ft;
- After a depth from 120-130 feet the next depth must be no deeper than 80 ft;
- After a depth from 95-110 feet the next depth must be no deeper than 70 ft;
- After a depth from 80-90 feet the next depth must be no deeper than 60 ft;
- After a depth from 65-75 feet the next depth must be no deeper than 50 ft;
- After a dive from 50-60 feet the next depth must be no deeper than 40 ft;
3. once you ascend to the next level you can't go deeper;
4. if you go deeper than 100 ft or come within three pressure groups of the ML on the last leg of the dive, you must do a 3 min safety stop at 15';
5. you must immediately ascend between levels at a rate not exceeding 60 fpm and cannot delay your ascent;
6. if you exceed an ML by 5 min or less, you are in an emergency decompression situation, you must ascend to 15' and complete an 8 minute decompression stop and not dive again for at least 6 hours, and if you exceed an ML more than 5 min, you are in an emergency decompression situation, you must ascend to 15' and complete a decompression stop of at least 15 minutes and not dive again for at least 24 hours.

If you apply the shorter MLs to the RDP and apply all the required rules, the only thing you're losing with multi-level dives on the RDP are the 5 ft depth intervals.

 

[DivemasterDennis]

It can be done as a multilevel dive with the RDP, but it's easier with the wheel. I still have a wheel, and I always dive with a computer. However, I do check my si against the wheel regularly, to keep that skill current, and regularly do a multilevel dive profile with the rdp for instructing purposes.

DivemasterDennis