Dive Planning and Computers Vs. Tables

[tombiowami]

After reading the posts concerning reliance on computers for nitrogen intake and bottom time I am wondering how many of you follow this as opposed to using the sqare diving profiles used by the tables? I am fairly new to the sport and coming from basic OW it seemed that most people are content to get a computer and just use it to follow as opposed to any real planning.
I have just started AOW/Nitrox and my trainer is a cave diver who said even on "easy" openwater dives he plans and uses the tables. He is a dive planning maniac, though I have to say I have learned tons of good stuff on the hows and whys. Especially having to plan air consumption and filling dive bags for salvatge. My OW class just touched on dive planning and air consumption rates. After listening to his reasoning I have to agree that while you don't get as much bottom time you get better margins of safety. In other words, use the computer as a backup for the tables/analog guages as opposed to the other way around. I know cave/tech is different in some regards than standard OW dives, but I wonder if they could use the computer and do not because of possible failure or dcs, why should open water divers do differently? The nitrogen intake schemes are the same.

Just wondering...

Tommy

 

[SubMariner]

Tom, you are certainly right that using the "flat tables" and a square profile will help you plan your dive more conservatively. However calculating a multi-dive day using only "flat tables" might penalize you sufficiently that you could wind up violating the flat tables even though you are well within safe limits diving with a PC. Not intentionally, but simply because of the dramatic difference over the course of several dives between one system that gives you "offgassing credit" for shallower depths, and the other that doesn't.

Meanwhile, you didn't mention WHICH tables: Nitrox or Air? There is a difference in uptake of N2 when diving on enriched air (Nitrox) vs "regular" air, as evidenced by differences in bottom time and allowable operating depths.

If I am using air, I plan my dives using The Wheel; it more closely resembles a dive PC & allows for multi-level dive profiles. However, if I am using nitrox, I plan either using my PC or my flat nitrox tables simply because they don't have a nitrox Wheel.

Either way, in the end I dive my PC but NEVER to the limits! I NEVER "ride the 0"!!!!

Take care, eh?!

~SubMariner~

 

[socaldiver]

Tom,

I dive with a computer also, but I actually only use it to record my time, depth and temp. Then I transfer the info to my logbook and use the tables to finish off my intake. Depending on depth and time I will do more extensive planning on future dives for that day.

I know quite a few times the computer would tell me I have a considerable amount of time before I hit NDL but in my ultraconservative method I feel safer. Normally on a dive I accomplish what I am down there for and have no needs or desires to push it to the limit.

 

[Newhampster]

Sort of.

I just came off a week of diving (18 dives, 5 and a half days). No way I could have done this diving on tables. I would have had to cut back my bottom time by at least 50 percent. Using Nitrox and a Cobra, this extended series was fine and I never came CLOSE to the conservative limits set in the computer.

 

[kauai_diver]

I have the same opinion as the "Hamster". Doing numerous dives over a couple days is hard to do using only tables. I mean when I go out on the boat with my friends, we take 4 bottles each. We plan our dives based on location, goal(ie. fishing, exploring etc...) depth expected and lastly time. I run the plan through the tables and inevidably would not be able to do all 4 dives unless we were out there for 12-14 hours so that we could get all of the interval times in etc...

I agree it is good to still look at and use tables to remain profficient and have that back up plan available if the technology pieces crap out, but in multi bottle dives you just get no credit for the variences and such using tables like you do with a computer. Diving Nitrox helps this but the computer really helps and I agree that the conservativeness of the computer adds a safety margin to it.

 

[Mario S Caner]

It's important to know how tables work. But using a computer is more efficient and more accurate. Learn the tables, understand the tables... use a computer.

 

[blacknet]

Hello,

One good method is the use the tables and the computer. Use the computer for logging purposes and emergencies and plan with the tables. This way you have backups and emergency provisions.

Ed

 

[jmsdiver]

I have to agree with Mario on this. It's important to understand the physiology behind the instrument that you use. A computer will give you "credit" for ascending to progressively shallower depths, thus effectively increasing your bottom time without hitting a NDL. And, many have the capacity to do Nitrox and track O2 sats. Your instructor is probably big on tables due to the type of diving he/she does; I don't know many technical divers that use computers, rather they plan their dives using tables and planning software (like Abysmal's) and take those planned data on tablets down with them so that they can do the deco. They use depth gauges and timers instead of computers and are very redundant. For the kind of diving that you are involved, I would recommend a computer. Computers offer the opportunity before diving to plan how long you may stay at a particular depth, and some offer the opportunity to simulate diving before diving.

Submariner, I believe that DSAT is developing (or has already) a Nitrox compatible Wheel....

 

[tombiowami]

I understand the computer credit and all, but were the tables not created with the expectation that you would be descending and ascending?

And if the tech divers do not use a computer, why is that different for rec divers? The nitrogen intake or oxygen partial is the same, does'nt matter if you are 60' in the cave or on the reef.

My conservativness is based on the one shot concept, one bad decision while diving can easily paralyze and/or kill.

Tommy

 

[blacknet]

Hello,

This is true about the kill part. However, in technical diving there is less margin of safety (because your in decompression) and you need all the safety you can get. Those 'techdivers' who do NOT use a computer for decompression, well lets just say that I disagree with them.

Navy manual states that you have top side support that keeps time and records. In the 'recreational' community you don't have this luxury so you must do it yourself. It's easier, more efficent and safer to invest in a dive computer. In 'technical diving' you have a specific goal to do, your depth/time is already planned out before hand, your gas is pre-planned and all you do is use something like a bottom timer to mark the time. In some cases you have pre-cut slates specific to your mixture. All that's left is to do the actual dive and match the numbers.

Another point. "tech divers" are more apt to go down for a specific task/job at a specific depth" (square profile) while "recreational" divers are more apt to change depths with the enviroment and do the "multi-level" dives.

Ed