Computers & DIR

[Scuba_Steve]

It's best to understand as much of the subject matter as you can, and we believe once you do that, you will conclude that dependency on in-water devices such as computers isn't as necessary as some would have you believe, nor is it as difficult to track NDL's in the absence of an in-water computer as some woudl have you believe.

Hope that helps.

Regards

Although I entirely agree, I can also say in the same breathe, relying on an inwater device doesn't predispose you to being unskilled or giving you inapropriate NDL information, which is a (weak) argument I hear AGAINST using computers for recreational diving from folks that are generally GUE trained. Sure you won't see me making the move back to computers any time soon.....as you say, they're not required.

But hey, I am truly pretty open minded.

As I said in a previous post, we have bigger fishes to fry with regards to diver skill than this topic. (Which I guess is what your first point is talking about).

Since the topic is not a core DIR-f study, I think this shows the (lack of) importance that is really placed on it.

Regards, and keep up the good work.

Steve

 

[MHK]

Although I entirely agree, I can also say in the same breathe, relying on an inwater device doesn't predispose you to being "dumb" or giving you inapropriate NDL information, which is a (weak) argument I hear AGAINST using computers for recreational diving.

Steve,

The potential for reliance on a computer and the predsiposition to being "dumb" is an argument that I avoid, I don't think they have anything to do with each other, one way or another. That said, I do believe there to be a correlation between a "lazy" factor once a diver develops a habit of relying on computers. I essentially think we agree on this issue.

However, I did want to speak to your second comment, specifically you wrote:

"or giving you inapropriate NDL information,"

I would respectfully disagree with this comment. While for certain computers are moving in the right direction, all too many of the in-water models rely on Buhlman, 60 FPM ascent rates, penalize you for deep stops, apply extreme conservation set points and so on. So in that regard, I do believe that they do provide, or atleast, have the ability to provide "inappropriate NDL information"..

Anyway, the larger point I'd like for everyone to consider is that it's all THEORETICAL based, and anyone looking for a mythical defining time certain is missing the point.

Hope that helps..

Regards,

 

[Doc Intrepid]

Thanks Mike. Regards and all...

Doc

 

[Scuba_Steve]

Hey MHK, you caught me before I editted my post to reflect a better way of putting it in print.

Agreed, I avoided the use of the word "dumb", but only after I initially used it LOL
It was a poor choice in words and I was correcting it.

I guess you can disagree on the inappropriateness of the NDL, but again we'd have to be specific on the computer used, which neither of us were, and besides, as we both agree, there is no written in stone NDL. At the Rec level, we are merely micro-managing an amount that neither of us can really quantify with any statistical significance, so the argument on it's face is quite moot.

If it gives you 5 mins more deco that our "on the fly methods", you may or may not need it, but how do you REALLY know if that's the case today?

We don't. Or........we try it and see.

I tend to not micro-manage Rec NDL theories, as it's useless, and as you say is missing the point. I'm merely showing the possible other side of the coin whilst being fair to those that don't think of it as we may, which by it's definition is being open minded on issues that are simply not black and white.

Regards, and thanks for your time.


Steve


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[rsanders]

There is no hard and fast formula, that I am aware of. It's a lot of estimation and common sense.

I know I'm hearing it Nth hand, but I've read the same thing in a few different threads now, and I find it increasingly spooky. Either it's a deterministic thing, which could be expressed in formulae or tables or even (gasp) on a computer, or it's not and no two divers will necessarily produce the same answers. And given the fact that one answer is probably going to be better than the other, that doesn't sound like a desirable condition. I know that the body is chaotic and not theoretically convenient and that all decompression theories are just approximations, but that isn't any less true just because you're doing the calculation on gray matter. So is GUE teaching people to use the Force or is there actual, predictable math involved?

Also, I had assumed this method was intended to be used as a very rough approximation when things went sideways, but it sounds like people are using this on the fly rather than following a pre-dive plan. Is that SOP?

-- Robert

 

[lamont]

I know I'm hearing it Nth hand, but I've read the same thing in a few different threads now, and I find it increasingly spooky.

Decompression theory is inherantly spooky. Dive computers and tables shield you from this.

Either it's a deterministic thing, which could be expressed in formulae or tables or even (gasp) on a computer, or it's not

It is not deterministic.

and no two divers will necessarily produce the same answers.

No two dive computers, dive planners or dive tables give the same answers about deco. At some point you have to be able to simply make a choice.

And given the fact that one answer is probably going to be better than the other, that doesn't sound like a desirable condition.

Take any two tables or dive computers or dive planners and try to pick which one has the best answer. Its the same problem. Why do you use the table/computer/planner that you do?

I know that the body is chaotic and not theoretically convenient and that all decompression theories are just approximations, but that isn't any less true just because you're doing the calculation on gray matter.

???

So is GUE teaching people to use the Force or is there actual, predictable math involved?

No, no two divers will necessarily agree.

Also, I had assumed this method was intended to be used as a very rough approximation when things went sideways, but it sounds like people are using this on the fly rather than following a pre-dive plan. Is that SOP?

Can't speak for GUE, but yes, I've got no problems diving like this on the fly. It is not a substitute for proper dive planning and obeying any hard limits on the dive imposed by the team in the predive brief, but sometimes you stray deeper/shallower or longer/shorter when the dive plan allows it and this allows you to adapt.

Look, its not magic. We're talking about estimating exponential solutions to differential equations at an accuracy sufficient to not get you bent. This is most of what I did for years when I sat down at a college mid-term in math or physics and tried to come up with an estimate to the answer to a problem first before I blew 10-15 minutes trying to solve it. For problems *much* harder than the entirely trivial math that dive computers do, I could usually get very close estimates by applying quick linear approximations.

 

[TSandM]

We're talking about estimating exponential solutions to differential equations at an accuracy sufficient to not get you bent. This is most of what I did for years when I sat down at a college mid-term in math or physics and tried to come up with an estimate to the answer to a problem first before I blew 10-15 minutes trying to solve it.

The more I read and learn about decompression theory and the derivation of the tables, the more I realize that this is not only not an exact science, but not even a well constructed model of the physiologic reality it is attempting to describe . . . the problem being that there are simply too many things which are not understood about how gases distribute in the body. The only good, objective evidence we have for how well we are doing with models is Doppler monitoring of bubbles (and are any bubbles bad? Or only so many bubbles? Or bubbles of "x" size? Or "y" bubbles per minute? Or does it matter where?) and the gross and unfortunate measure of bent divers.

A number of different models have been developed to attempt to predict gas distribution and elimination. They have been "validated" by divers who have used them, who either recorded DCS events, or submitted to Doppler monitoring on the surface. We pretty much know that, if you dive within certain algorithms (and assuming you have no conditions that make them invalid for that dive), your risk of DCS is very low. We do NOT know if you can reorganize the decompression part of the dive (the ascent, because ALL ascents are decompression events) and truncate the decompression time/stops and still be safe. There is some evidence that you can.

Computers use algorithms, and anybody who owns a computer ought to know a little bit about which algorithm the computer is using and what assumptions are made in its construction, and what validation has been done (at least I think so, anyway).

I am really looking forward to perhaps learning something about how I can do my own calculations of the multi-level, terrain-based dives that are almost all I do, to serve as a double-check and perhaps eventually as a substitute for the algorithm in my computer.

 

[waynne fowler]

well, of course you follow your backup dive plan. which is why i carry a watch
and tables with me on every dive...

until you find a better way of doing it, which is what my question was designed
to do...

where do i find out, other than the fundies books (and J.J.'s books), which cover
the subject in abysmal paucity, the real nuts and bolts of diving without a computer?

i guess i'll have to take DIR-F again, since my class didn't cover this
important aspect. and personally, i am not willing to let go of the computer
without one-on-one instruction on the subject, real-time.

You don't have to take the Fundi's again. Though it probably couldn't hurt it may not provide you with the answers you seek. If I were you I'd first look to my instructors. See if you can get any information out of them. There are some real simple basic things that they can show and tell you that will equip you as well as you can be to help you begin to master the concepts of MDL's, ascent rates etc... However you will have to do a bit of research on your own beyond what they can tell/provide you. You should find them most helpful in pointing you down the proper path.

process sounds very simple, but i want to make sure i learn it right.

also, is computer failure really that much of a worry? doesn't DIR teach us
to disregard "fake" failure points and concentrate on real ones?

to me, a computer is much less a failure point than a single first stage, and
yet DIR does not prohibit diving with a single first stage.

Wise you are young obi-won on all the aforementioned points.:god:
But in our focus on the most/more probable failure points we don't discount those of lesser probability. I still use my vyper.. albeit only as a gauge. I've seen way more 1'st stages go during a dive then I have seen computers... But I have seen computers go As a side note.. many 1st stage failures can be fixed right then.. if your computer dumps.. well now you probably have a $300 - $500 paper weight.

Be Safe, Learn all you can. Pick your instructors brain.

Enjoy the Dive

 

[Nemrod]

Where is there obtainable a copy of the exact tables recommended by DIR/GUE to print or purchase and where is there a text explaining the application of these tables? Where can we get them? Thanks. N

 

[salty]

Where is there obtainable a copy of the exact tables recommended by DIR/GUE to print or purchase and where is there a text explaining the application of these tables? Where can we get them? Thanks. N

www.wkpp.org