Why you can't use the PADI RDP table for Multi-Level dives

[jale]

Hi
Good to see a thread about using tables for multi-level dives
The use of tables as multi-level planner was quite a.common practice before computers become so easily available. Personally i think it is a good tool in you "knowledge box" as it gives a better awareness of the diving parameters' interconnections and makes divers think a bit beyond the "I follow my expensive computer" nonsense...

 

[TMHeimer]

Hi
Good to see a thread about using tables for multi-level dives
The use of tables as multi-level planner was quite a.common practice before computers become so easily available. Personally i think it is a good tool in you "knowledge box" as it gives a better awareness of the diving parameters' interconnections and makes divers think a bit beyond the "I follow my expensive computer" nonsense...

I can see learning to plan multi level dives with only the RDP could be an interesting task to master. But I agree with Tursiops--would never use it for actual diving. Not when computers are available, or even the eRDPml. Plus, think I'm way too lazy to do that table work (and I know the RDP & nitrox ones back & forth).

 

[Eric Sedletzky]

A person could possibly figure out a very crude estimate of a multi level dive from a square table but they’d have to be a mathematical freak of nature to even get close. 99.9 % of the people on earth do not have this capability.
In order to try to calculate an accurate ML profile off a square profile table you’d have to be able to figure in all the descent time and each depth increment plus total time getting to the deepest depth, then time spent at deepest depth, then the time it takes to ascend to the next level. You’d have to be able to keep track of ALL the depth history plus time, then you’d have to come up with a time percentage of BT used at each depth thus far (which is not linear, each deeper depth has different saturation rates for each compartment). When you come up to 70’ from deeper it is different than coming down to 70’ from above. You’re already more rapidly taking on gas in different tissues from being deeper so your allowable BT time at the new depth is not the same. You cannot average all your depths based on the DSAT table and come up with some arbitrary number and call that the depth you can base you NDL on. Some agencies claim you can but then they make no claims that they are NDL times and are calling all their dives “Deco” based dives with a stop at half max depth then stops at 30-20-10 on every dive. This is not NDL diving where you can theoretically come right up if desired.
Some very smart people developed the tables. Don’t pretend that you’re smarter than them and can outsmart their work because you can’t. Leave decompression science to the experts and buy a really good computer, much easier worry free and makes more sense for us that do not have PhD’s in science.
That said, there are times I do not dive with a computer because I do a lot of shore diving which involves hunting and hands on action. The depths and times never even come close to any NDL and my dives are limited by air supply. A computer just gets banged up and or lost so for those dives I don’t need it.

 

[tursiops]

A person could possibly figure out a very crude estimate of a multi level dive from a square table but they’d have to be a mathematical freak of nature to even get close. 99.9 % of the people on earth do not have this capability.
In order to try to calculate an accurate ML profile off a square profile table you’d have to be able to figure in all the descent time and each depth increment plus total time getting to the deepest depth, then time spent at deepest depth, then the time it takes to ascend to the next level. You’d have to be able to keep track of ALL the depth history plus time, then you’d have to come up with a time percentage of BT used at each depth thus far (which is not linear, each deeper depth has different saturation rates for each compartment). When you come up to 70’ from deeper it is different than coming down to 70’ from above. You’re already more rapidly taking on gas in different tissues from being deeper so your allowable BT time at the new depth is not the same. You cannot average all your depths based on the DSAT table and come up with some arbitrary number and call that the depth you can base you NDL on. Some agencies claim you can but then they make no claims that they are NDL times and are calling all their dives “Deco” based dives with a stop at half max depth then stops at 30-20-10 on every dive. This is not NDL diving where you can theoretically come right up if desired.
Some very smart people developed the tables. Don’t pretend that you’re smarter than them and can outsmart their work because you can’t. Leave decompression science to the experts and buy a really good computer, much easier worry free and makes more sense for us that do not have PhD’s in science.
That said, there are times I do not dive with a computer because I do a lot of shore diving which involves hunting and hands on action. The depths and times never even come close to any NDL and my dives are limited by air supply. A computer just gets banged up and or lost so for those dives I don’t need it.

Read the Duis (1991) paper. It is not hard to use the RDP to mimic the ML profile of the Wheel.

 

[boulderjohn]

I assume this means that this means you should plan your deepest dive first? I thought this was no longer mandated as in fact you can do a shallower first dive to say 15m then a second dive to 25m?

It is not mandated. If you have enough surface interval to do your next planned dive, you can do it, even if it is deeper than the one before.

On the other hand, if you do the deeper dives first, you will be able to do the other dive sooner; it will require less surface interval.

 

[Storker]

For the really adventurous:
A procedure to validly use the RDP table for multi-level dives was published by Duis (1991), after the Wheel came out but long before the eRDPml. The procedure was developed to be consistent with the Wheel. It has two constraints: (1) each level must be significantly shallower than the preceding level (60 ft to 35 ft is OK, but 60 ft to 40 ft is not, for example), and (2) at each new level the allowable adjusted NDL is less than the table shows. One could mark up their RDP table to include these adjustments, and have a satisfactory multi-level table planning too.

Your post headline claims that one can't use the RDP for multilevel dives, and then you go ahead and cite a paper that shows how one can use the RDP to galvanize multilevel dives. May I be a mite confused as to what you're trying to say?

I've used that approach to analyze multilevel dives and compared the output to the Suunto dive planning tool. They've deviated by only a couple minutes as to the maximum run time.

 

[tursiops]

May I be a mite confused as to what you're trying to say?

No. The RDP cannot validly be used all by itself, with the danger being that you go into deco without knowing it.
The Duis paper uses the RDP to mimic the Wheel, but requires extra procedures that are not part of the RDP.

 

[Blackcrusader]

It is not mandated. If you have enough surface interval to do your next planned dive, you can do it, even if it is deeper than the one before. On the other hand, if you do the deeper dives first, you will be able to do the other dive sooner; it will require less surface interval.

Thanks all I was clearing up is that many divers still believe that they have to do the deeper dive first. They are often planned this way by dive centers as well. There are many times a dive may do their morning dive at say 8:30am. their afternoon dive at 2pm and a night dive at 6pm and have 3 hours surface interval or more between dives. At least for me. Even when I am doing 4 dives I would do two morning dives with an hour plus the two dives, an afternoon dive with another 2 hour plus surface interval and a night dive with another 2.5 - 3 hour surface interval. Normally the dive times are around an hour when doing this for me.

 

[tursiops]

The use of tables as multi-level planner was quite a.common practice before computers become so easily available.

It was wrong then, and it is wrong now. Apparently you did not read my explanation in ht OP.

 

[jale]

It was wrong then, and it is wrong now. Apparently you did not read my explanation in ht OP.

Well it is not because you say that it wrong that it is wrong
The procedures used were validated by COMEX and even they became a law. Yes an offcial law.