Multi level dives

[Dody]

I post this in the new diver forum but I think that the answer should come from experienced divers and probably those interested in science.
The diving tables tell you what the NDL is. I know that they should only be used for U shape dive profiles bit some use them for multilevel dives.
Let’s say that your NDL at 40 meters is 5 minutes and is 10 minutes at 30 meters. Some people believe that you can stay 4 minutes at 40 meters and then go to 30 meters as if the previous part of the dive with the on-gassing did not exist. Is it right?
Of course, we have DC today but some people still use tables for such dives.

 

[Centrals]

I post this in the new diver forum but I think that the answer should come from experienced divers and probably those interested in science.
The diving tables tell you what the NDL is. I know that they should only be used for U shape dive profiles bit some use them for multilevel dives.
Let’s say that your NDL at 40 meters is 5 minutes and is 10 minutes at 30 meters. Some people believe that you can stay 4 minutes at 40 meters and then go to 30 meters as if the previous part of the dive with the on-gassing did not exist. Is it right?
Of course, we have DC today but some people still use tables for such dives.

I have no idea how to use table to plan a multi-level dive.
I was taught to use the "wheel".

The PADI Wheel — Dive Instructor Academy

 

[inquisit]

No, it's not right. There is an entire section of the table devoted to residual nitrogen time. While it's not correct to consider a multi-level dive as two dives with zero surface interval, doing so would highlight the error of ignoring the first level's accumulated nitrogen.

 

[Lostdiver71]

The tables do not support multilevel diving. There are apps you can use to plan multilevel dives or get yourself an inexpensive dive computer for under $200 or even less on sale.

 

[OTF]

I'm sorry to be insulting and bring in drama from another thread. But if you got to DM level without being able to explain the answer to this question, in detail, to students - you were ripped off and you need to find new instructors. Dive tables don't work like that at all.

Assuming you're diving air and using conservative gradient factors, the dive you describe (4 minutes at 40m followed by 10 minutes at 30m) would require 4 minutes of mandatory staged decompression (not just a safety stop). This isn't a "big" deco dive, but it's certainly off the NDL tables and should only be done with deco training and a redundant gas supply.

 

[TMHeimer]

When I boat dive it is almost always square profiles. I use computer and watch/depth gauge. The odd time I do an actual multi level dive (not just being at 80' most of the time except going up & down 20' to crossover a wreck deck), I just use the computer. I would guess that most divers don't plan anywhere near exacty 10 minutes at this depth, ascend, then 20 minutes at this shallower one, etc. Probably more like "I'll stay here a while unless it's gets boring, then I'll ascend some".
I too would not use tables to plan multi-level dives. Or PADI's eRDMml--interesting toy but only practical for practice exercises.
Either way, no, you can't ignore any part of the dive regarding ongassing. Unless you start getting into depths of like 20 feet. That's a different topic.

 

[Centrals]

What happened to the PADI "Wheel"?
Not teaching anymore because of dc?
It was very useful for me when I did not have dc and did not want to be restricted at 18m(on a LoB in GBR).

 

[Lostdiver71]

What happened to the PADI "Wheel"?
Not teaching anymore because of dc?
It was very useful for me when I did not have dc and did not want to be restricted at 18m(on a LoB in GBR).

The wheel was never very popular and was discontinued with the release of inexpensive dive computers.

 

[tursiops]

some use them for multilevel dives.

They are using the tables incorrectly.

Is it right?

No

some people still use tables for such dives.

Why you can't use the PADI RDP table for Multi-Level dives
also
https://www.scubaboard.com/community/threads/erdpml-padi.606462

What happened to the PADI "Wheel"?

The wheel was never very popular and was discontinued with the release of inexpensive dive computers.

Discontinued in favor of a calculator app, the eRDPml, which is still available. Kinda fun to play with.
.::Electronic Recreational Dive Planner - eRDPML::.

 

[Centrals]

The wheel was never very popular and was discontinued with the release of inexpensive dive computers.

I knew it was not popular because I had never seen anyone using it and only used it on one trip myself.
But it was good to know that table has limitation.
Plenty divers wouldn't know what we are talking about.
Should had still kept it as part of "multi-level" speciality course.