Repetitive Dive Table Problems

[Bruce Herold]

Subject: Repetitive Dive Table Problems
I was reviewing some repetitive dive table problems for a refresher and I noticed some rather large discrepancies in the results when comparing US Navy Dive Tables with Naui Dive Tables. After I worked this repetitive dive problem, the results for a 50 foot dive ranged from 79 minutes (using US Navy tables) to 59 minutes (using Naui tables). When I reviewed the answer key from the internet (use of what dive table is unknown to me) the result was 49 minutes at the same depth of 50 feet.
My quick review of the Padi Dive tables appears to be giving me even something different yet.
Letter Group Designations vary also. The Padi Dive Table I am looking at ranges from A to Z. The Naui Dive Table by Kessler ranges from A to L. The modified US Navy Dive Table by Reuter ranges from A to O, stops then ends with Z.
I can understand being conservative and having some safety built is but 79 minutes to 49 minutes seems huge.
Can someone explain?

Bruce Herold

 

[RJP]

You'll need to share more details on the FIRST dive for anyone to comment on the repetitive dive.

On air, PADI says 75min (W diver) before exceeding NDL, NAUI says 80min and V-Planner is allowing me 73min before giving me a mandatory stop on a first dive.

Of course V-planner is also telling me I need 151cf of gas... so there's that.

I don't know Navy tables well, but it sounds like you're not getting a "repetitive" dive out of USN.

 

[boulderjohn]

I don't know anything about the NAUI tables.

The PADI tables are completely different from the U.S. Navy tables and will give you very different results. They are designed for different diving than done in the Navy, and the title of the table announces that. Here are some key differences.

1. The primary incentive for PADI to build different tables was the very long surface intervals required by the Navy tables. It made it very, very hard to do two tank recreational dives. The Navy tables use the 120 minute compartment to guide surface intervals. That is why the whole thing washes out in 6 iterations of that, or 12 hours. PADI's research indicated that the 40 minute compartment could be used for the dives included in that table, but they used the 60 minute compartment to be more conservative. That is why that table washes out in 6 iterations of that, or 6 hours.

2. In order to further shorten the surface intervals and make two dive trips feasible, PADI lowered the maximum first dive times.

3. PADI further made many more pressure groups. This cut down on the amount of rounding off that is required for repetitive dive calculations.

 

[Basking Ridge Diver]

I am confused by what you are asking - I am using the NAUI Tables - 50feet = 80 min dive on the first dive.

NAUI Dive Tables

What are you using to get your repetitive dive? Can you share the values so I can work your problem?

*** Backed into it Letter Group C - your first dive was 15 mins at 50 feet and second dive at 50 feet would be maximum at 59 mins. ***

 

[boulderjohn]

---

---

A ScubaBoard Staff Message...

repeated threads merged.

---

 

[tbone1004]

quick clarification

NAUI tables are essentially identical to the USN NDL Air tables. They are one stop short to add in extra safety. These tables were optimized for the Navy's general practice of one long dive per day.

PADI went and made their own tables to maximize repetitive dives, so on the first dive, or the deepest dive, you'll have shorter NDL's, but on subsequent dives, especially those with shorter surface intervals, your NDL's will on average be longer. Obviously there are exceptions to the rule, but that is the generalization. Choose your tables wisely, if you are doing say NC wreck diving, or West Coast diving, you may want to dive Navy/NAUI tables if you are going relatively deep and have relatively long surface intervals. If you are in the caribbean and doing a bunch of shallow dives, you may want to choose the PADI tables which will offer you better NDL's for your repetitive diving.

 

[BRT]

Or get a computer and get longer NDL times for first and second dives in most recreational settings.

 

[Crowley]

The US Navy tables and the PADI tables are based on different mathematical models, the reason for which has been given above in that there is a huge difference between what the US Navy was doing at the time, and the recreational diving as promoted by PADI.

The Original US Navy tables were developed in the 1950s, the DSAT/PADI RDP in the late '80s, based on the difference between the two styles of diving - and most modern recreational computers use a variant of the mathematical model behind the RDP with a few additional extras such as the RGBM (Reduced Gradient Bubble Model) which incorporates mathematics that a physical table is not capable of displaying unless it was about 2 kilometres wide!

The different tables are not compatible, were designed for different styles of diving and without the use of computers, the RDP is far more relevant to recreational diving than the US Navy tables, even though some agencies have not adopted it. The letter designations are merely artefacts of the table design and are not meaningful in any other way. Ending up in pressure group H on one table is not the same as ending up in pressure group H on another. Ending up in pressure group X on the RDP is not necessarily a bad thing, it just affects calculations for repetitive dives.

It's a complex subject but I hope that helps a bit

C.

 

[Doc]

As Crowley inferred above- USN tables were designed for "square" profiles. Jump in, go to set depth, perform task, ascend.

To further explain dive tables, PADI and others devoleped Repetitive Dive Planners using data that considered "multi level" diving.

The best use of tables is the understanding they will lay as a foundation for understanding a dive computer. Knowledge of the algebra will give you a basis for altering the parameters of a programmable computer.

Fun story: For her first 100+ dives, my wife religiously ran her dive tables. There was no convincing her that on Day 2 of doing 5x a day, she had violated her tables and could have been declared legally dead by PADI or any other national certifying agency. It did teach her how her computer thinks, though.

 

[tursiops]

Fun story: For her first 100+ dives, my wife religiously ran her dive tables. There was no convincing her that on Day 2 of doing 5x a day, she had violated her tables and could have been declared legally dead by PADI or any other national certifying agency. It did teach her how her computer thinks, though.

I have no idea what you mean by this. If she followed the tables, how could she have violated the tables and "died?"