Logging Nitrox Dives in a regular Dive Log

[lolskim2008]

Hi I'm a new nitrox diver and I was finally catching up on my logbook and came across the problem of accurately logging the nitrogen group I was in. I never really worried too much about this as I was using a dive watch that did precise algorithmic calculations for me. After doing all the EAD (equivalent air depth) calculations of the certain mix I was diving I noticed that the depths in some cases didn't change too much and would end up placing me in the same nitrogen group that a person diving regular air for the same dive would be placed in. The tables I'm using are standard NAUI dive tables for regular air, now I understand that Naui tables are already one of the more conservative tables out there but since this is the format about 50 of my dives are in my logbook I'd like to stick with that if possible. So what it comes down to is I was wondering if anyone has found anything so my Naui tables aren't telling me I should definitely be bent when my dive watch is telling me i've got another 10 minutes left of diving at depth. Any tips or anything would be greatly appreciated since I'd really like to keep an accurate log of my dives. Thanks!

 

[k ellis]

well this is one reason many instructors tell you to go by your computer vs. the tables. Tables even in air are based on maximum depth period. So if you go to say 60 feet for one minute then come up to 20 feet and spend the remainder of your time at 20 feet you still go off the tables 60 foot range.

Computers take the guess work out of logging dives and calculations during the dive such as adjusting your NDL based upon current depth and previous depth on this dive. It will adjust constantly therefore many instructors I have spoken too have suggested bypassing the pressure groups and rely on the computers. I know some people on here will flame me for this but I am merely speaking what I have been taught.

 

[lolskim2008]

I absolutely agree with placing a great deal on computers as well, a partial solution to this that I was thinking but not sure how accurate this would be, but when I transfer my dive information to my computer from my watch it tells me my average depth, what would be the legitimacy of using this to calculate my pressure groups. As a side note I obviously wouldnt use that to determine my next dives but rather just for the sake of logging my dives.

 

[kaerius]

The way I do it is writing a bunch of boxes in the comments.

XX
XX
XX
 XX
 XX
 XX
  XX
  XX
  XX

Like that.

In the boxes I put

Depth|Time
EAD|PG
PPO2|NDL

And then I put another set of boxes, staggered out one step, for each additional level of a multilevel dive(usually 3 levels).

I do one of those(+O2 exposure for the whole dive) before going in, as my plan, and one post-dive, for what I actually dived(typically shorter times than plan). That's in addition to diving with my computer set for the nitrox mix I'm diving.

Sample dive:

25% O2 exposure (plan)          20% O2 exposure (actual)
30|20                                  30|17
24.4|L                                 24.1|J
1.28|27                               1.28|27
   18|10                                  20|3
   14.1|P                                 15.8|L
   0.9|20                                 0.96|37
      12|10                                  12|6
      8.9|R                                   8.9|M
      0.7|112                                0.7|136

Mind you I learned PADI, so different tables I guess, but you get the gist of it I hope. And the profile above was my very first nitrox dive(about a hundred dives ago, with a group of 8).

 

[k ellis]

I absolutely agree with placing a great deal on computers as well, a partial solution to this that I was thinking but not sure how accurate this would be, but when I transfer my dive information to my computer from my watch it tells me my average depth, what would be the legitimacy of using this to calculate my pressure groups. As a side note I obviously wouldnt use that to determine my next dives but rather just for the sake of logging my dives.

thats a scenario I never thought of but would probably work good for the sake of the paperwork Avg depth would kind of give you a proximity to where you could start

 

[Bubbletrubble]

Many novice divers ask this exact question when first using their dive computer.

Don't use your average depth to back out your pressure group.

If you want to figure out what your pressure group is after a given multi-level dive using a computer, just enter the planning mode immediately after surfacing and take note of the NDLs at all of the listed depths. Match up the NDLs that your computer spits out with the NDLs of your NAUI dive tables. Enter the resulting pressure group in your written dive log.

For example, after your dive (diving a regular air mix), you surface and your computer planning mode reports the following NDLs: 40ft. 25 min., 50ft. 19 min., 60 ft. 16 min., 70ft. 13 min., 80 ft. 11 min., 90ft. 10 min., 100ft. 9 min., etc. Using the PADI air dive tables (I don't own the NAUI version), this translates to a Pressure Group of D. This method would work for 32% nitrox as well provided that you change the O2% setting to 21% when writing down the NDLs for various depths (when correlating to air tables). No need to change the setting if you are using 32% nitrox tables.

FWIW, most divers who use a dive computer don't even bother writing down their pressure group following a dive. Obviously, the computer tracks all of this for you and will re-calculate NDLs for various depths on subsequent dives. When diving tables, it makes sense to record the pressure group by hand.

 

[k ellis]

Many novice divers ask this exact question when first using their dive computer.

Don't use your average depth to back out your pressure group.

If you want to figure out what your pressure group is after a given multi-level dive using a computer, just enter the planning mode immediately after surfacing and take note of the NDLs at all of the listed depths. Match up the NDLs that your computer spits out with the NDLs of your NAUI dive tables. Enter the resulting pressure group in your written dive log.

For example, after your dive (diving a regular air mix), you surface and your computer planning mode reports the following NDLs: 40ft. 25 min., 50ft. 19 min., 60 ft. 16 min., 70ft. 13 min., 80 ft. 11 min., 90ft. 10 min., 100ft. 9 min., etc. Using the PADI air dive tables (I don't own the NAUI version), this translates to a Pressure Group of D. This method would work for 32% nitrox as well provided that you change the O2% setting to 21% when writing down the NDLs for various depths (when correlating to air tables). No need to change the setting if you are using 32% nitrox tables.

FWIW, most divers who use a dive computer don't even bother writing down their pressure group following a dive. Obviously, the computer tracks all of this for you and will re-calculate NDLs for various depths on subsequent dives. When diving tables, it makes sense to record the pressure group by hand.

Very well said!

 

[1_T_Submariner]

I just write computer dive in the log with Time Depth Etc... I don't worry about groups when diving a computer because I would have been off the tables on some trips.