USN, NAUI and PADI Dive Table differences...

[Bruce Herold]

I am calculating repetitive dive profiles using USN, NAUI and PADI tables. My results from the PADI tables differ so much from the other two, it makes me wonder if I am doing something wrong.

Here is the profile...

83ft/18", 3hrs surface interval, 60ft/32", 1 hr surface interval. What is the NDL for 40ft, 50ft, 60ft and 70ft? Including RNT's with TNT's (total nitrogen time) would be of great! Any and all help would be greatly appreciated!

Bruce H

 

[RJP]

Did you review the responses to your previous two threads on this topic? The differences between USN and PADI were explained pretty clearly.

What numbers are you getting for NDLs between PADI and NAUI?

 

[Bruce Herold]

In general it was explain. But now I'm looking at specific numbers.

I'm looking at PADI RDP DST tables. Based on my given profile, the way I interpret these tables is 40ft/113 w/RNT@27, TT@140

50ft/59, RNT@21, TT@80

60ft/38, RNT@17, TT@55

70ft/25, RNT@15, TT@40

 

[tbone1004]

look, go ask an instructor, I'll repeat the gist of my post from earlier.

NAUI=USN less one stop basically. Where the NAUI tables list mandatory stops, the USN tables just end. It was their way of factoring in a little conservatism. Based on one long dive maybe two dives with a long surface interval in between.

PADI didn't like this, so they made their own, they optimized theirs for short surface intervals and repetitive diving, so on the first dive you lose some bottom time but you pick it back up on subsequent dives.

second point, there is no "interpretation" of dive tables, they are what they are, if you don't get the same numbers as someone who knows what they're doing, you're doing it wrong. They are black and white, no room for any gray area. You violated tables or you didn't, oh you ducked to 62' for a second, well if you're diving tables you just went to 70' if you're following them properly.

conveniently your results from the usn and naui tables should be the same for RNT coming in, your NDL's will be different.

NAUI and USN tables you come out as a G diver, RNT is 73/56/44/37 down the line. Straight forward. Your AMDT is going to be different by some ungodly number for 40ft, 20min at 50, then 5 and 5. NAUI AMDT should be 57/24/11/8

I don't have PADI tables in front of me, but the numbers should be longer which is normal.

 

[tursiops]

Your numbers are correct, but your interpretation of them may not be, if you think they are problematic.
When you (for example) say "50ft/59, RNT@21, TT@80" that should mean: after dive #1 to 83 ft for 18 minutes followed by a 3h surface interval, you did dive #2 to 60 ft for 32 minutes, followed by a 1h surface interval, and then you consider dive #3 to 50 ft, and you have a No Decompression Limit of 59 minutes. That is because the total time allowed at 50 ft is 80 minutes, and you have a residual nitrogen level already in your body of 21 minutes, so only 59 minutes still remain to be used.

If this is what you understand, then what is the problem?

Also, when you say "Navy tables," which ones do you mean? There are many.....

---------- Post added May 17th, 2015 at 10:08 PM ----------

Your numbers are correct, but your interpretation of them may not be, if you think they are problematic.
When you (for example) say "50ft/59, RNT@21, TT@80" that should mean: after dive #1 to 83 ft for 18 minutes followed by a 3h surface interval, you did dive #2 to 60 ft for 32 minutes, followed by a 1h surface interval, and then you consider dive #3 to 50 ft, and you have a No Decompression Limit of 59 minutes. That is because the total time allowed at 50 ft is 80 minutes, and you have a residual nitrogen level already in your body of 21 minutes, so only 59 minutes still remain to be used.

If this is what you understand, then what is the problem?

Also, when you say "Navy tables," which ones do you mean? There are many.....

Additional:
I had some old IANTD, TDI, and Navy tables lying around, so took a look at them.
The IANTD and TDI tables (c2004-2005) were both based on Buhlmann; they both said your dive #3 to 50 ft had 59 mins NDL (just like the PADI table!).
The Navy table gave 44 mins for dive #3 to 50 ft. The Navy table appears to be the same as the one in the NOAA Dive Manual, which is the 1999 Navy version.

I checked the NAUI website for their tables. They are essentially the same as the Navy tables, of course, except they give a shorter NDL. Thus, dives #1 and #2 come out the same as the Navy table, because neither dive hits the NDL. Dive #3 has the same RNT at 50 ft (56 mins), but only 24 mins NDL remain instead of the 44 mins on the Navy table....that is just NAUI's conservatism approach with the shorter NDLs than Navy uses.

In summary, for your dive #3 to 50 ft, your allowed NDL is 59 mins (PADI/IANTD/TDI), 44 mins (Navy), and 24 mins (NAUI).

Is this what you got?
Best of all, the differences are completely understandable and not a surprise.