Ratio Deco
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I took the Ratio Deco class from AG. He had another UTD instructor in the room assisting him. This instructor had a variety of deco planning software on a computer. Each time we did an RD profile, that instructor would do the same profile on one of those programs, and each time the result would be different. That difference was used to show how very wrong those programs were, because they did not match the RD "proper" profile. "Proper" was the precise word used the contast the RD profile with what the various software programs produced.
OP
For AG, what has he done to develop/prove etc, his version of ratio deco? How does it differ from any other versions of ratio deco? How did they develop/prove their version?
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---------- Post added July 22nd, 2015 at 02:30 PM ----------
I remember you mentioning that before, certainly made me think. How long ago was that?
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That was in December 2010. I dropped out of UTD almost immediately after that.
OP
I can give a partial answer about the differences.
Back when I was in UTD and arguing about things, I was particularly concerned about two aspects of the UTD Ratio Deco. One was the S-Curve, which I thought was nuts. I read the document on which that "oxygen window" theory was based, and my immediate reaction was WTF? When you analyze the only small section in which it appears, you see that the conclusion is totally ex nihlo--the conclusion is not derived from the preceding data. I argued strenuously against it, and I was finally mollified by being allowed to straighten out the curve a little on our diving. The second reason was the belief that there was no need to take altitude into account in dive planning. AG said altitude did not matter, and when I asked him the basis for that belief, he said that he knew it did not matter because he dived at Lake Tahoe using straight RD, and he was fine. (I was doing most of my deco diving at altitude, and I was very concerned.)
At that time, someone put me in touch with Jarrod Jablonski, and he and I had a very nice and informative exchange regarding the GUE version. He admitted that the theory on which the S-curve was based now looked to be wrong. He said they were keeping it, though, because it had been working in the past. (I have since been told it has been dropped.) He said that the origin of RD for GUE was based on DecoPlanner. When you use a program like that, you usually make contingency plans in case you deviate from your dive plan. They noticed that they could predict contingency plans with reasonable reliability within a certain range by using a mathematical construct. The purpose was to use this mathematical construct to be able to recreate accurately what would have been created by DecoPlanner. (The mathematical construct they use is different from the one UTD uses, but I can't tell you how.) As for altitude, he said they had never tested RD's ability to recreate a valid deco profile at altitude, so he could not recommend using it. He said it seemed to me you would have to be increasingly more conservative as altitude increased.
I don't know if UTD still uses the S-curve. When I took the official class, AG knew I had been raising a stink about it, and he, too, said the theory was suspect, but he came up with two other reasons to keep using it. I don't remember either one. I don't know of any other changes that may have taken place in the years since I dropped out.
PfcAJ
Contributor
GUE's ratio deco mimics the output from buhlmann 20/85 or VPM+2. If the ratio does not equal (within a few minutes, lets be pragmatic here) deco planner's output, the ratio is wrong.
An example is 21/35 at 150' with 50% as deco gas as "1:1". Through a range of times around 30mins, its pretty darn good. But at 45mins of BT the ratio is off by 15mins (buhlmann) or 7mins (VPM+2).
Well what to do?
You can ignore the algorithm and just do your ratio deco (even though according to the decompression software its not enough time) or abandon the ratio method and do the extra time.
For short BTs and relatively light gas burdens, the difference in time might not result in DCS. But as your deco times get longer, your risk % goes up EVEN IF you hold the algorithm constraints constant. So now your risk is going up (just by virtue of having a longer prescribed deco schedule) AND you're cutting time because you want to hold on to some 'ratio'? That's no good.
Then there's the whole deep stops thing (which NEDU's study would suggest is a less-than-ideal strategy), the s-curve oxygen window thing (which is bunk), not adjusting for altitude (physics still applies), and now apparently you don't need surface intervals?
Its irresponsible to be teaching decompression in this manner.
"iresponsible" is a very polite word here.
The only way Ratio Deco can make sense is if ALL the models are so incredibly conservative and they are ALL safe and so you can fudge around between them add/subtract a few minutes here and there and it doesn't make any difference. But, we know this is not true......
PfcAJ
Contributor
If you are accurately recreating an established deco program based on solid theory, then your ratio deco profile will be as safe as that established deco program based on sold theory. It should work. When you get outside of that, then you have to ask for the basis on which you are making that plan. There is a difference between celebrating that your plan recreates an established program and celebrating that it does not recreate an established program.
So what is the theory behind a program that does not recreate an established program? My first attempt at formal RD training was actually in a Webinar conducted by AG. It was a two parter, and I only got the first part. In that Webinar, a woman asked AG for the theory behind the plan he was teaching. She wanted to know how she could be sure what she was being taught would work. He said, "You have to have faith." She answered, "Faith in you?" He replied, "Yes."
That may seem to be an outlier, but I asked AG similar questions. His answers can be summarized as "It works for me."
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