Place of dive tables in modern diving (Split from the basic thread)

[Kevrumbo]

The metric PADI RDP shows 9 mins NDL for 40m, not 10 mins for 130 ft, even though 40m and 130 ft are often (sloppily) used interchangeably. However, Pressure Group A does not even exist on the metric table for 40m; you use PG B, which is 5 mins RNT, so you'd only have 9-5=4 mins NDL at 40m.

Show me the schedule, using PADI RDP, that lets me dive to 40 metres for 9 minutes, and then dive to 40 metres for 9 minutes at some later point. It should be doable, right? When? The best I can offer is 24 hours and that number is not in the tables.

There is no mystery with this. The metric tables show 9 mins at 40m, exiting in PG G. After 4h42min SI, you can do it again. That's right off the table, side 1, clear as day. What is the problem?

PADI Wheel RDP shows 10min at 130fsw (39msw) for NDL with PG H;
After 1h50min SI, the new PG is A; After 4h30min SI, the PG is "blank" which implies you can do the above again;
Repetitive dive with PG A yields 7min at 39msw for NDL with ending PG H.

 

[boulderjohn]

There is no mystery with this. The metric tables show 9 mins at 40m, exiting in PG G. After 4h42min SI, you can do it again. That's right off the table, side 1, clear as day. What is the problem?

I believe the problem goes back to his original statement on this--he believes that someone doing the first dive is in the A pressure group, and the A pressure group does not allow it. A diver doing a first dive is not in a pressure group. If you reach the end of the surface interval range for the A group, you are also no longer in a pressure group. You are starting over as a new diver.

 

[markmud]

Hello OP,

For me, the tables were/are a training aid and a basic reference guide. I am glad to know how they work. Just as I am very glad that I can navigate oceans the "old school way" using paper charts, Coast Pilot, tide tables, current data, compass, DR, fathometer, and sextant.

I reference dive tables occasionally before doing an advanced recreational dive as a plan "B". I reference navy tables before doing an advanced recreational dive as a plan "B" just in case I over stay my NDL and end up in deco. I have an understanding of what my computer is trying to tell me because of the tables.

That is how I learn--it is a "me" thing.

As to the Chairman's post regarding extra safety stop time, I do the same thing but differently. I usually do 30 seconds at 30 feet, 3 minutes at 20 feet and 1 minute at 10 feet. Just because. I do see a lot while doing this procedure. My diving is not over at 20 feet.

I also see things like the skipper who kept engaging the propeller while divers were at the swim step. What an unsafe action. The people on the surface and huddled around the swim step did not know that.

markm

 

[markmud]

ADDED AS AN AFTERTHOUGHT:
This demonstrably reinforces the concept that tables are hard for people to use....

Hi tursiops,

The tables are not that difficult. Yeah, you have to study them and learn how they work, but they are not difficult.



Hi tursiops,

The tables are not that difficult. Yeah, you have to study them and learn how they work, but they are not difficult.

The tables are hard for some people to use who don't want to learn how to use them.

Maybe we should be discussing the attitude of some divers as perpetuated by some industry leaders that diving is benign and safe like walking through a suburban park. Lets make a distinction: diving can be as safe as walking through a suburban park, if you are educated properly and understand the decompression issues. "All dives are decompression dives."

But that is for another thread.

markm

 

[dmaziuk]

If you reach the end of the surface interval range for the A group, you are also no longer in a pressure group. You are starting over as a new diver.

So then if my SI is 6:01, I'm OK to fly?

Why do you keep talking about a second dive? And are you talking about 40m or 130 ft?

I'm talking about 5 atmospheres and I don't care if you measure them in cuns or millifurlongs. I dive to 40 m for 9 minutes and end up in pressure group G. I then want to dive to 40 m for 9 minutes again, I flip the page over and look for the column in table 3 for pressure group "none" that lets me do that. It's not there. The best I can do is pressure group A and NDL of 7 minutes.

I then go to table 2 and find out that I need SI of 1:42 to go from G to A. My residual is now 2 and I can got to 40 m for 7 minutes, +2, and land in group G gain. so from this point on the table is self-consistent. But in order to go to full 9 minutes, I need an outside intervention: @boulderjohn has to come in and tell me that I need SI of 4:43.

 

[tursiops]

So then if my SI is 6:01, I'm OK to fly?

No, the same table tells you the rules on flying after diving. 6h is good enough to dive again, but not to fly.

I'm talking about 5 atmospheres and I don't care if you measure them in cuns or millifurlongs. I dive to 40 m for 9 minutes and end up in pressure group G. I then want to dive to 40 m for 9 minutes again, I flip the page over and look for the column in table 3 for pressure group "none" that lets me do that. It's not there. The best I can do is pressure group A and NDL of 7 minutes.

I then go to table 2 and find out that I need SI of 1:42 to go from G to A. My residual is now 2 and I can got to 40 m for 7 minutes, +2, and land in group G gain. so from this point on the table is self-consistent. But in order to go to full 9 minutes, I need an outside intervention: @boulderjohn has to come in and tell me that I need SI of 4:43.

Stay on the front of the RDP. Look at the Table 2 SI credit table. Follow G over to the right; in the last column on the right, it says you are in PG A if your SI is between 1:42 and 4:42. After 4:42 you are not in a PG anymore. Go diving, spend 9 minutes at 40m.If you are not in a PG, then there is no info in Table 3 that is applicable to you. Note the text on side 2, however, at the bottom left where the rules for Flying After Diving (FAD) are.

 

[boulderjohn]

So then if my SI is 6:01, I'm OK to fly?

Could be. That has not been researched enough to know for sure. There was no research done on flying after diving as a part of the RDP development.

I'm talking about 5 atmospheres and I don't care if you measure them in cuns or millifurlongs. I dive to 40 m for 9 minutes and end up in pressure group G. I then want to dive to 40 m for 9 minutes again, I flip the page over and look for the column in table 3 for pressure group "none" that lets me do that. It's not there. The best I can do is pressure group A and NDL of 7 minutes.

That's right. As long as you are within the limits of a pressure group, that option is not open to you.

I then go to table 2 and find out that I need SI of 1:42 to go from G to A. My residual is now 2 and I can got to 40 m for 7 minutes, +2, and land in group G gain. so from this point on the table is self-consistent. But in order to go to full 9 minutes, I need an outside intervention: @boulderjohn has to come in and tell me that I need SI of 4:43.

You will notice that each of the pressure groups has a range--it is 2 numbers, not one. When you get out of that range, you are no longer in that pressure group.

 

[Dan_P]

My view on the matter is this - I have started with my personal conclusion, and then elaboration in a few bullets points.

Conclusion
As you will see in the highlighted bullets below, RDP excels at nothing over using either computers or Min Deco.
In every case, one of the two latter are stronger candidates.
This is why I think it will in time be replaced by those two.

Which of the two one might want to use, is a different conversation.

Ease of use
Computers are hands down the easiest to use, and I dare say Min Deco is a lot easier than the RDP as well, particularly in-water (behold the above exchange). But computers are the easiest by far (the downside is risk of complacency, but I feel it's fair to keep that a separate matter).

Adaptability
With RDP it's possible to maintain an in-water overview in the face of dive parametres changing in real-time, but Min Deco is truly excellent for this particular purpose. Computers less so, as they are of a reactive nature in that regard.

Scalability
Some computers can be scaled to use throughout all one's diving - but not all, and those that can, are usually more expensive than the more basic ones. And even if one has a scalable computer, it's common to amend/check it with a separate pre-planned dive schedule.
This is arguably the most common approach in technical diving.
RDP works for a single gas and in no-deco only. Different gas means a different slate, and they're all out the window when one advances to technical diving. That is, this solution excels as the the only one that is absolutely, certainly not scalable.
Min Deco scales into Ratio Deco, keeping a consistant line across Day 1 and Day 10.000.

Educational value
Everything else aside - using Min Deco (and/or Ratio Deco) in a training setting offers a highly potent teaching opportunity and tool.
One may not like it for anything else, but this is one single point that I honestly think is damn well near indisputable.

Cost
RDP is cheap (Min Deco is indifferently cheaper as one doesn't need to purchase plastic charts), but computers really are quite easily available now. One can get a fine recreational nitrox computer with compass and all sorts of nifty bits and bobs for, say, a couple of hundred bucks. The cost difference between that and the cost of a bottom timer or analog depth/time-devices, is small enough that this really shouldn't be the main reason for choosing one or the other.

Effectiveness
I've added this point to leave it intendedly open.

 

[boulderjohn]

RDP excels at nothing over using either computers or Min Deco.

Since in 20 years of diving the only person I have ever seen try to use the RDP for diving is myself, and that did not work because we were doing multi-level dives, I am not an advocate of using it for dive planning. However, the RDP excels at something far, far beyond Min Deco. It was developed as a result of thorough research using Doppler bubbling imaging in thousands of dives and divers. That research as led by scientists of the highest repute.

Min Deco was developed by whom after what studies?

 

[scubadada]

Since in 20 years of diving the only person I have ever seen try to use the RDP for diving is myself, and that did not work because we were doing multi-level dives, I am not an advocate of using it for dive planning. However, the RDP excels at something far, far beyond Min Deco. It was developed as a result of thorough research using Doppler bubbling imgain in thousands of dives and divers. That research as led by scientists of the highest repute.

Min Deco was developed by. whom after what studies?

Deco for Divers, Mark Powell, 2014, p 176:

The DSAT Recreational Dive Planner (PADI) model (1987)
The M-values used for the RDP were adopted from the Doppler bubble testing and tested by Dr Merrill Spencer and tested by Dr Raymond E Rogers, Dr Michael R Powell, and the colleagues with Diving Science and Technology Corp, a corporate affiliate of PADI. The DSAT M-values were empirically verified with extensive hyperbaric chamber and in water diver testing and Doppler monitoring.