DIR and computers

[Custer]

kwesler once bubbled...
to consider is this...

I had to pull a diver out of a bad situation she got herself into as a result of a lack of understanding of what the computer is actually doing. Perhaps this will be addressed as agencies "teach" computers. In this case, as a relatively new diver, she dropped to 120 ft. (off the agreed on plan of 80'), and did not look at her computer often enough. It was her first dive to that depth (first deeper than 60') and she had no idea how fast her computer would put her in deco at that depth. If you do not have a good idea of at least the tables, and at best the theories BEHIND both tables and computers, you cannot even effectively use a computer. Not ot beat dead horse, but even a 5 minute interval at 120' on air is not enough for a newish diver to check air and NDL, UNLESS they understand the principles and physics behind the calculations.

In this case, I do not think the issue was because of not diving the plan...I believe she did not understand WHY there is a plan, and WHY the plan is monitored, either with the computer between her ears or the one on her wrist.

You have a pretty convoluted assessment of causality here.

What happened to this chick had nothing to do with tables, or especially, her computer.

kwesler once bubbled...
BTW-isn't it SOP to have a redundant depth gauge and timer?

Ken

Who's SOP?

 

[DSJ]

cornfed once bubbled...


How do you get the pressure group?

I put the computer in dive plan mode and scroll through the allowed bottom time for each ten foot increment. Taking this information I just work the table 3 backwards. I found it didn't really matter which depth I used, but I still scanned from 40' to 80' and took the more conservative number. The actual group you get will vary with your set of dive tables.

An Example:

Step 1)
I surface and scroll through the allowed BT's, finding that I'm allowed 18 minutes at 70'.

Step 2)
I flip my handy PADI recreational dive planner to the repetative dive table (table 3) (http://www.stud.ntnu.no/~playboy/diving/diving.html) and run my finger across the 70' row until I hit 18 (or fewer which would give me the higher group number) minutes allowed BT.

Step 3)
I run my finger up that column to find that I'm currently a "J" diver.

It's pretty simple exercise.

David

 

[mattengstrom]

I think a big part of the "benefit" of computers comes in when they're compared against the tables. Take my "official" education to date (as opposed to unofficial from reading this board ) on the use of tables. Your max depth on a dive is the depth you use on the tables, along with the total time of the dive, to figure out your pressure group. OK, simple enough.

So, after certification and on my first vacation to Grand Cayman, I rented a computer. And just for kicks, and because I like to use my brain, I also ran through the table calculations.

In many cases, the dive profiles for the morning went something like this: Wall dive to 100-110 feet, spending 7-10 minutes at that depth, then slowly come back up to the top of the wall, and stay at that depth, usually 60 feet or so, until it was time to surface. Total dive time was usually around 30-35 minutes.

Now, according to the tables, these dives were all "illegal" because I should have come up after 16 minutes after a dive to 110 feet. So, by using a computer, I was able to extend my bottom time because it took into account our slow ascent to the top of the wall and our extended time spent at 60 feet.

Now, if I had been taught multi-level dive planning or the use of the wheel, instead of straight tables, things may be different. Point being that for someone who has only been exposed to tables and computers, computers give you more "wet time."

 

[cnidae]

DSJ once bubbled...
I use a computer (Sunto Cobra) with the RGBM model (or at least it claims to), but I don't turn off my brain when I use it.
I believe that every diver should learn the tables and the theory behind them.

I think your missing some of the points. The computer & tables your using do not give you stops, they only give you ceilings so to learn the theory behind your computer and tables would be an out of date education. Another is the computer is not customized to your body; I've felt terrible after dives were my computer was fine. I've also had the above-mentioned computer screw up on a dive. Another point is GUE divers try to come up clean, not come up with the notion they won't have to go to the chamber after they arise from the water.

 

[DSJ]

mattengstrom once bubbled...
I think a big part of the "benefit" of computers comes in when they're compared against the tables

That's true, and to give Mike his due he did say

Thirdly, many divers are sold on the computer as a way to extend bottom times. That is partially true when the choice is limited to tables -v- computers.

I believe that the DIR folks use a "step wise" computation which gives them a multi-level "wheel" like ability on the fly by using the average depth for a given five minute interval. Sort of like a poor man's computer.

Is this right Mike?

David

 

[MHK]

DSJ once bubbled...


That's true, and to give Mike his due he did say



I believe that the DIR folks use a "step wise" computation which gives them a multi-level "wheel" like ability on the fly by using the average depth for a given five minute interval. Sort of like a poor man's computer.

Is this right Mike?

David

In fact, hat is exactly what I was trying to communicate. Basically, in short, the Buhlman algorithm has two subsets, ironically enough called subset B and subset C, and the point is that when you strictly limit the comparison to which can give you more BT the table [ which computes in planned time] versus the computer [ which computes in real time] then of course the answer is the computer. That being said, there are more then two options when you factor in the gradient conservation associated with most in-water computers so my point is that you need to extend the logic and thought process beyond computer -v- tables..

Hope that helps..

 

[DSJ]

cnidae once bubbled...


I think your missing some of the points. The computer & tables your using do not give you stops, they only give you ceilings so to learn the theory behind your computer and tables would be an out of date education. Another is the computer is not customized to your body; I've felt terrible after dives were my computer was fine. I've also had the above-mentioned computer screw up on a dive. Another point is GUE divers try to come up clean, not come up with the notion they won't have to go to the chamber after they arise from the water.

I'm using the computer for recreational no-decompression dives, so I have no stops outside of the standard safety stop.

I'm not clear as to why the tables are an outdated education for recreational dive planning. For deco diving yes, absolutely. But then the tables state clearly that they are not to be used for decompression diving.

I'm not sure what you mean about customizing the computer to your body. If you've had swings in both directions, then which way do you know to adjust? The Cobra actually will adjust to both altitude and body conditions. I can set a conservation factor according to my altitude and one of three "personal" settings, each one more conserative than the last. So if I've left off my exercise for too long I could bump the conservation level up a notch.

As for coming up clean, I follow the RGBM model with a max 30 fpm ascent rate. Starting the dive at the deepest with a gradual ascent to shallower depths to finish off the dive should keep me as clean of bubbles as any other method, should it not?

David

 

[DSJ]

MHK once bubbled...


...there are more then two options when you factor in the gradient conservation associated with most in-water computers so my point is that you need to extend the logic and thought process beyond computer -v- tables..

Hope that helps..

So if I understand you correctly you are saying that DIR divers don't use a computer because they run a continuous computation as they dive using a DIR taught algorithm.

That would be a good reason that DIR folks don't use them, but what would you offer the non-DIR trained folks? I think most people take the DIR non-computer philosophy as a general condemnation of computers since the only alternative they have is the tables. Given the vast difference in bottom time on most multi-level dives folks would rebel at that.

I know that DIR doesn't address non-DIR divers, but it might do more to clear up misconceptions.

David

 

[MHK]

DSJ once bubbled...


So if I understand you correctly you are saying that DIR divers don't use a computer because they run a continuous computation as they dive using a DIR taught algorithm.

That would be a good reason that DIR folks don't use them, but what would you offer the non-DIR trained folks? I think most people take the DIR non-computer philosophy as a general condemnation of computers since the only alternative they have is the tables. Given the vast difference in bottom time on most multi-level dives folks would rebel at that.

I know that DIR doesn't address non-DIR divers, but it might do more to clear up misconceptions.

David

David,

Let me see if I can be somewhat more clear on your point, but some issues are simply more difficult then others to communicate via interent forums..

Ideally, as you may be aware, we approach DIR as a holostic approach. To that end I'm not exactly sure how to compare and contrast DIR -v- non-DIR with respect to multi-level diving. I can speak to the DIR approach but I'm hesitatnt to speak on behalf of the non-DIR approach partly because the non-DIR approach has no uniformity to it and may very well differ from one diver to the next.

That being said, when you look at our approach a DIR diver need only remember two numbers[ ie; 120 and 20%] so the whole "memorizing" tables discussion gets tossed out the window, and frankly if a diver can't remember 120 & 20% then my sense is they have little business diving because it ain't that hard to simply remember two numbers. To that end, once we accept the premise that you only need two numbers, then all a diver needs to do is take 5 minute snap shots of his dive to compute average depth.. Take your average depth, apply the 20% rule and the 120 rule and away you go.. It's really quit simple and I suspect people make more of it then it needs to be in part because they were never taught it in the first place, and secondly it would diminish sales of computers..

Hope that helps..

 

[DSJ]

MHK once bubbled...


I'm not exactly sure how to compare and contrast DIR -v- non-DIR with respect to multi-level diving

Actually what I was asking is what you would suggest folks use if they don't use the DIR 120 20% rule.

From what I have gathered so far, this is taught in the DIR-F class and the details are not taught in an open forum to make sure that whoever hears it really "gets it" and doesn't hurt themselves with an imperfect understanding.

Given that no agency outside of GUE teaches your method, that leaves everyone with three options:
Dive tables
The Wheel
Dive Computers

When folks hear that DIR doesn't like computers they rarely hear about the 120 20% rule and assume the alternative is the tables. This causes a bit of unintended backlash as folks say, "What? Take away my multi-level diving capablility because some fool doesn't know what's behind the computer and rides the no-deco display? No Way!"

From what I hear you feel the best method is the 120 20% rule, but absent that, what do you say to everyone?

A) Stick with the dive tables
or
B) Feel free to use a computer, but learn the tables, read the manual, and think

David