Tables & computers

[fjpatrum]

I just finished the online TDI Nitrox course (which is tables based) and it made me think quite a bit about how I've been diving. I chose the TDI nitrox course over the SDI nitrox course (computer based--no tables) because I was given to understand there is more theory in the TDI course than the SDI offering.

My OW course used the eRDPml from PADI but also explained the tables. To me, the tables are quite intuitive and very easy to use. I have used the RDP exactly once since OW class, and that was while sitting in my living room comparing it against tables...

Now, when I dive I use a dive computer. Before each dive, though, I check my NDL for my expected average depth against the tables and set a countdown timer for that # on a watch. When/if I hear the alarm on my countdown watch, I ascend, period. This is making me (perhaps) overly conservative if I'm spending a short portion of my dive deep and a long portion shallow, but it seems like a good method of ensuring I'm not pushing NDLs too badly.

I'm clearly not using my computer to its full advantage/potential but I understand the tables a lot more clearly than I know what's happening in my computer.

Do a lot of people dive this way? IE using tables as a basis but the computer for the details?

[TSandM]

You're definitely being very conservative.

What you could think about is that the tables are derived from calculating the nitrogen loading at a given depth for a given time. It's a simple calculation. On the other hand, the computer is doing the SAME calculation, but doing it iteratively during the dive, and much more closely represents the actual nitrogen exposure you have. In addition, you need to realize that, on any dive, there's a certain depth above which you are effectively decompressing; although you may still be loading the very slow compartments, they're essentially meaningless in normal exposure recreational diving. Time spent above this ceiling should not be penalized from a nitrogen standpoint. So, for example, if you do a dive to 80 feet on a Florida reef, the time you spend from 30 feet to the surface is decompression, and shouldn't count toward your table time. (Remember, the tables count bottom time as running until you start your ASCENT -- on a multi-level diver, it can be difficult to figure out when that is, but at some point, you are effectively ascending.)

[Searcaigh]

For years I used tables, then the PADI Wheel, even when I got my first computer (Suunto Companion) back in the 90's I planned my dive roughly in the same profile for most of my rec diving 20M for 20mins, 16M for 20mins then 10M and less for the remainder, with sort of slight deviations depending on what I found to photograph.

Deeper than 20M was actually out of norm because most of the good stuff was 20M an shallower. If there was something deeper then I planned for it on tables first - Longnose Hawkfish on black coral at 35M, some wreck diving hitting 25-30M allowing for a deeper multilevel dive still using the wheel.

To be honest now I tend to dive by computer, but I know what my NDLs are beforehand at the most depths, but rarely dive square profiles apart from one 15-16M site and usually on 36% Nitrox to give me a long bottom time at that site. Tables and Wheel are always in my dry box on the boat and I wear a watch as well as a computer.

[Hatul]

Realistically no one I know uses dive tables to dive. We all use computers for recreational diving. It's good to know how to use the tables and what the air groups means, but they're from Jacques Cousteau days.

[fjpatrum]

Interesting, thanks for the input. I have only hit my NDL timer once but I've been within a few minutes of NDL (on the computer) several times depending upon the depth I was at the time.

I really hadn't considered that shallower depths may be effectively deco time though so I'll see how that comes into play. I was mostly using the tables because they seem intuitive to me and it is an easy way to make sure I'm not doing anything stupid by blindly following the computer...

[FPDocMatt]

Wow, it's been about 2 weeks since I asked the same question. So these things really do run in 2-week cycles after all.

I can't wait to try out my new computer. Counting down the days....

[BrotherBear]

Interesting, thanks for the input. I have only hit my NDL timer once but I've been within a few minutes of NDL (on the computer) several times depending upon the depth I was at the time.

I really hadn't considered that shallower depths may be effectively deco time though so I'll see how that comes into play. I was mostly using the tables because they seem intuitive to me and it is an easy way to make sure I'm not doing anything stupid by blindly following the computer...

Is your computer air integrated and does it specifically say "NDL Time" or is it RBT for Remaining Bottom Time? I'm a bit of an air hog and my AI computer usually counts down RBT but it's based on air consumption and remaining air supply...unless I'm on my doubles or diving (too) deep I'm rarely capable of exceeding NDLs.

[Prof Diver]

I use both really. I have all my tables in my log book folder and yet I still use my computer.

The man reason for this, that there is a small degree is plan tables for multi-level diving, unless you use a wheel. So I have my computer to make sure I don't go over the limits. Also, I need my computer as it is air integrated.

[Pullmyfinger]

Wow, it's been about 2 weeks since I asked the same question. So these things really do run in 2-week cycles after all.

I can't wait to try out my new computer. Counting down the days....

That's seems to be about right Matt,
The upside is that there ends up being a lot of good responses over time.

-Mitch

[Pullmyfinger]

Realistically no one I know uses dive tables to dive. We all use computers for recreational diving. It's good to know how to use the tables and what the air groups means, but they're from Jacques Cousteau days.

I dive tables, but I have to agree, I don't see them used much by other divers.
For the first dive many divers probably know the NDL for the various depths off the top of their head....it's possible that they are "diving the tables" even though they don't actually take them out.

That's just a guess on my part, and probably not a correct one. Because I see most divers with computers.

I have a computer (Dive Rite Nitek Duo), but I use it in gauge mode along with a Uwatec bottom timer.
I started diving tables prior to taking Advanced Nitrox/Deco procedures, and used tables cut from V-planner during that course. Since I'm diving tables for those types of dives, I use tables for recreational dives also.

I was originally taught to use tables anyway. After I got the Nitek Duo, I still compared everything to the tables.

Computer are probably the best tool for the job, which is why most divers use one. I prefer tables, mostly out of familiarity and simplicity.

-Mitch