computers and dive tables

[David K]

David: I do not believe that diving a computer and using your head are mutually exclusive.

Nor do I, there are few absolutes in life, taxes & death being two of them.

Reflecting on my own experience I can say that early on using a dive computer gave me confidence & reduced my task loading. As I gained experience my dive computer was the last piece of gear I became comfortable with. It was difficult to interpret under water, especially when I strayed beyond NDL. I exceeded NDL so infrequently that I could never remember how to interpret the strange flashing symbols on my dive computer.

Learning to dive in gauge mode required me to pay closer attention to my profile & understand how dive tables & dive computer algorithms relate to one another. I found this level of understanding very rewarding as it permitted me & my noggin to control the dive.

David K

 

[TSandM]

I did a dive last night to approximately 80 feet . . . for eighty minutes. That dive didn't fit in any table. I was wearing a computer (Mosquito) and a gauge (Vytec). The computer was never unhappy with the dive, and neither was I, as I mentally monitored it using the data from the Vytec (which I can see, as opposed to the Mosquito, where only the NDL is big enough to see easily in the dark).

Tables would have been useless for evaluating or analyzing this dive, unless I were willing to do a lot more work than I am. What IS useful is what I've learned about decompression, decompression algorithms, and the shape of the deco curve. I use some basic data and judgment to decide what a reasonable profile is, and cross-check it with the computer, because I just don't have enough confidence in my own ability to store and evaluate data underwater yet.

So yes, once I got a computer, I stopped using tables, but that was because I asked many questions about applying tables to the kinds of multi-level, terrain-based diving I was doing, and I didn't get any descriptions of how it could reasonably be done. I don't cross-check the computer with tables; I cross-check the computer with data and my current understanding of models, and to this point, I would bow to the computer were it to tell me I had erred. It hasn't yet, and eventually I may give up that bit of redundancy.

 

[cummings66]

Cummings: You need to think through the scenarios a bit ...

Just because you can't do a "multilevel computer dive" and somehow match a table exactly you think that tables aren't useful. That's very limited thinking. If you have a 1 hour SI, after one of your hundret foot dives, how much NDL will you have? Is it

OK, then lets use Lynn's example 80 feet 80 minutes dive, and to be even more liberal we'll assume we're diving EANx32 instead of air.

My DSAT RDP says this NDL limit is 45 minutes, we did 80 which broke it by 35 minutes. Now refer to the back, it says this.

"EMERGENCY DECOMPRESSION - If a no decompression limit is exceeded by no more than 5 minutes, an 8 minute decompression stop at 15 feet is mandatory. Upon surfacing, the diver must remain out of the water for at least 6 hours prior to making another dive. If a no decompression limit is exceeded by more than 5 minutes, a 15 foot decompression stop of no less than 15 minutes is urged (air supply permitting). Upon surfacing, the diver must remain out of the water for at least 24 hours prior to making another dive."

Now you tell me, we exceeded the limit by 35 minutes. Following the RDP how are we going to figure a dive after a 1 hour SI when going strictly by the RDP you clearly must remain out for 24 hours. As I said, there is no way on Earth a table can back a computer as this quoted text clearly shows.

What I am saying and the others have said is this, if you follow the tables (not a wheel) and you use your computer to gain dive time, if you adhere to using tables correctly per the written instructions on the card then you're done diving. The tables forbid another dive.

Charlie has a very good idea as far as groups go, the computer normally wouldn't forbid another dive and it's pretty safe to assume worst case by table and use it, but strictly adhering to table values means NO MORE DIVING for 24 hours as the quoted text shows.

In other words it's like being half way pregnant. If you're going to use tables then use them, if you're going to use a computer then use it. Don't delude yourself that a table can backup a computer in all cases by simply inking in the numbers and following them. If you don't have the understanding and haven't been following good dive profiles and your computer takes a break, follow the tables and stop diving. If you've been conservative and have the understanding then I'd say do what you understand, but remember this was a question asked by a newer diver about computers and tables and therefore they most likely do not have the knowledge a DIR or other technical diver might about diving and probably did their ascents based on how their PADI,SSI, etc course taught them.

 

[Charlie99]

Learning to dive in gauge mode required me to pay closer attention to my profile & understand how dive tables & dive computer algorithms relate to one another. I found this level of understanding very rewarding as it permitted me & my noggin to control the dive.

Some of us have the mental discipline to have the dive computer running as a dive computer and still pay attention to our profile and control the dive using our noggin.

TSandM's post above is an example of using her brain and the computer as redundant checks of each other.

Another common misconception is that the computer somehow dictates your profile.

Except in some rare cases, like some DIR-approved profiles which would have you surfacing having not completed mandatory deco (of even an unpadded ZHL16B model!), one can dive any reasonable profile and the computer goes along for the ride while staying happy.

 

[cummings66]

That's a good thought and I think an accurate one. Just because you have a computer on does not mean you forget your profile and dive plan.

I know I've met guys diving who didn't understand a thing the computer said and just dove their tables (manditory computer usage), and I've met those that didn't understand a thing about the tables and relied completely on the computer(lazy) and I've met a few that seemed to just be in harmony with the universe while diving.

I believe that having a working knowledge of how both operate and how to use them is the best course of action.

An example of computers gone wrong would be a dive I did about a month ago with a boat buddy. He never dove cold water, only Warm waters and never used a computer either. We discussed our dive plan and agreed on it, the problem was I didn't realize at that point he never used a computer before. We both referred to the tables to make the initial plan and did our gear checks. I noticed his computer read out in meters but said nothing because some people just are different and have their reasons. I was diving EANx32 and so made clear what my MOD was for that mix.

We get in and the first thing he does is drop like a lead brick so I follow to make sure he's ok. He is. Then he takes off leading the way (violation of plan) and heads down, down, down. He's swimming like hell going down and doesn't seem like he's going to stop, and he's a fast swimmer putting his all into it for some reason (narc'd). Once we hit 100 feet and he's still hell bent on going deeper I decide to stop him, but it was tough since he was a stronger swimmer and at 123 feet I grab his fin. It was all I could do to catch him that way. He stops and I point out he's exceeded our depth limits and to go up. He acts funny and I persuade him to ascend. We get to 80 feet and he starts acting normal and we continue the dive for a bit and surface. Nowhere near the boat because he managed to run low on air. I wonder why? He didn't seem to know.

During the debrief do you know what his initial problem was besides from not following our plan? He was following that computer and thought it was in feet. He meant to go down to 100 meters max and would have had I not managed to catch him which wasn't easy. You would have thought with it being dark and all his diving having been in the ocean that he would have wondered how deep he was. Nope, I guess he had heard our lakes are dark and cold and that was it.

I learned some new lessons that day, and I won't assume things now that I would have trusted a diver to know. I've got a saying that I'll dive with anybody at least once, that day it got pushed to it's limits and a computer combined with a diver never having used one who acted like he knew how nearly caused problems.

 

[jeckyll]

OK, then lets use Lynn's example 80 feet 80 minutes dive, and to be even more liberal we'll assume we're diving EANx32 instead of air.
...

See, you can't do that.

I know you're probably not trying to see what I'm saying but I'll type it up again (as I did earlier in the thread I believe).

You need to use _your_ knowledge about _your_ 'standard profile' to gauge _your_ remaining exposure for the next dive.

If _I_ do a typical dive to 80 feet on air with 10 minutes at depth, 10 minutes between 60 and 40 feet, a minute at 40, a minute at 30 and the remaining time above 20 for a total runtime of 40 - 49 minutes, then I _know_ what _my_ adjusted NDL will be after an hour survace interval. I can do 30 min @ 60 or 40 min at 50 with no problems for dive 2 and I _know_ that's within any tracking system you want to use.

And _I_ can have my computer blow up and do a second dive with no problems. And that knowledge is NOT transferrable to you cyberdiving.

Your definition of 'backing your dive up with a computer' is different than mine, but try and think through what I said.

 

[plot]

See, you can't do that.

I know you're probably not trying to see what I'm saying but I'll type it up again (as I did earlier in the thread I believe).

You need to use _your_ knowledge about _your_ 'standard profile' to gauge _your_ remaining exposure for the next dive.

If _I_ do a typical dive to 80 feet on air with 10 minutes at depth, 10 minutes between 60 and 40 feet, a minute at 40, a minute at 30 and the remaining time above 20 for a total runtime of 40 - 49 minutes, then I _know_ what _my_ adjusted NDL will be after an hour survace interval. I can do 30 min @ 60 or 40 min at 50 with no problems for dive 2 and I _know_ that's within any tracking system you want to use.

And _I_ can have my computer blow up and do a second dive with no problems. And that knowledge is NOT transferrable to you cyberdiving.

Your definition of 'backing your dive up with a computer' is different than mine, but try and think through what I said.

I see what you're saying, you're keeping a very rigid dive profile in your mind as you go along. Even in this situation though, a dive computer crunching the numbers for you and watching when you stray off this rigid dive profile is still a huge safety mechanism.

There's a lot of mistakes that can be made when doing multilevel dive calculations manually via the tables. I'm not saying anyone on here is going to make them as you table guys probably do them routinely enough that you either double check them or you notice when something is off (ie: you think in your head you should have around 10 minutes at 60 feet left and your calcs show an hour or something)... but for alot of divers (especially the average rec diver), mistakes in calculations can, have, and will be made.

And to be honest, if I lose the use of my computer during a dive, I'd take it as a bad oman and call the rest of the day aynways.

 

[cummings66]

See, you can't do that.

I know you're probably not trying to see what I'm saying but I'll type it up again (as I did earlier in the thread I believe).

I understand what you're saying.

The average diver is not trained to do anything other than whip out the RDP follow the column and come up with a number, that's the reality of OW classes now a days. What you're doing is beyond that and IMO I made an error in how I answered the question giving more bias to the new diver progressing in diving vs the second part where he asked why or why not did they continue to use tables. I made the assumption he meant use the tables as taught in class, not as a general guide.

I think I made a mistake so the answer is yes. You use them and I continue to use them. I suspect neither of us would use them as we did when we first started diving. That is the answer to the question. We simply are not talking about what is the best way to do it, that wasn't the question at all. There is no point in arguing that fact in this thread because it didn't ask it.

I'm a conservative diver, I don't push limits and never will. I used to be an explorer and push things, I've broken bones and ended up in hospital a few times do to the push the limits attitude. In the past I'd be diving today, but since I hurt my back I'm waiting until I'm 100% before I dive again. That's because I'm older, have a young 3.5 year old daughter and wife and I want to be around to enjoy them. So, the old explorer is gone and I'm sticking to safer paths. If there's training to do something safer I'll take it, no more am I out in front leading the charge, that was for when I was younger, single and indestructible. I have responsibilities now and I'm conservative in what I do because of it.

I hope that nutshell of info about myself explains why I believe a table can not backup a computer for the average diver with OW training. I truly understand what you're doing, but it's not something I believe is 100% safe for the average diver.

For what it's worth I consider myself to be an average diver, I'm certainly not the best nor do I harbor illusions I will soon be. I'll do what I was trained to do as safely as I can. If that means no more diving then that's what happens. There is always tomorrow.

PS, I'm not old. I am 40 nearing my next birthday on January 13. I have a lot left to learn and do given time.

 

[meesier42]

I still plan ALL of my dives on the tables. And I even with a computer I still carry a slate with me that I write the appropriate time/ depth and contingency time/depth limits on. But I am new to the computer and don't rely on it.

 

[jeckyll]

cummings66: I completely agree, the _average OW_ diver can't do what I was saying. I don't think that the average coming out of OW training is much too low.



I am very conservative with my diving (one of my buddies calls me "Mr. Safety") but I also like to learn alot about how things work and I think most people who have 50 - 100 dives could do exactly the same, if they keep learning and don't turn off their brain . And I'm not at a point where I would give up my computer, but I don't look at the NDL remaining all that much given my profiles (there are examples for deep dives of course).

Dive often, dive safe

Bjorn

P.S.: I'm 35, so we're pretty close age wise