What is Ratio Deco?

[Diver0001]

Those two statements don't make any sense. RD (the way GUE teaches it) is verified as much as VPM or Buhlmann is. If 20mins at depth results in 20mins on the 50% bottle and 20mins on 100% via a buhlmann table (which is a pretty good algorithm), then its the same with RD. You verify the 'ratio' with decompression planning software through the depth/time range of your planned dive.

I know there have been some statements to that effect and some attempts have been made to devise experiments. I don't know how much progress has been made. If anything I would expect experiments to more clearly define the limitations of the technique than to verify that it can be used interchangeably.

I could be wrong, but I'm suspicious because there has been a tendency in the past to want to shield the technique from scrutiny related to decompression accidents. The same is true of RGBM, which was "verified" (as it were) in a similar way, using human guinea pigs in non-controlled environments and blaming computer programmers when divers got bent.

I'm not a purist about decompression strategies in the least. What works works, but the verification method should be held to as much scrutiny as the results in order for divers to form an intelligent idea of the relative strengths and weaknesses of given approaches. Like I said, I'm skeptical as to whether or not this has begun to happen in any meaningful sense.

All this is to say that your idea of verification and my idea of verification may not be the same. It's a question of definitions. To me a UTD article claiming that they have verified the validity of their pet algorithm is like the butcher certifying his own meat. If we want real verification then UTD should be consulted but in no way responsible for designing the experiment or analyzing the results. It should withstand independent scrutiny.

There's not a whole lot of mental math needed for RD, and it really becomes easy of you do the same types of dives all the time. If you're doing different depths/BTs every time you go out, then I would suggest taking tables with you.

There is NO mental math involved when you use a computer. I'm not as good at arithmetic as a computer. That's a fact that I'm willing to face.

R..

---------- Post added November 14th, 2014 at 01:38 PM ----------

And it happened 6 years ago . . .just because you & other 'tards like to mention it over & over en schadenfreud -it happened once six years ago with lessons already well learned: you miscalculate or fail to follow any deco algorithm profile, your chances of DCS will increase. Period.

Easy, Kev.

You made a mistake and you were man enough to write about it so we could all learn from it. So you're human. Big deal. Welcome to the club.

People bring it up because it's a good example of what can go wrong, even to a competent diver. It's not because they want to keep laughing it up at your expense.

If there's any karma involved, it might be related to being headstrong when you should have been long on listening. I'm sure you learned that too. For my part I don't know ANYONE ... especially people I can count on to get things done ... who isn't headstrong and short on listening sometimes. Again, it just makes you human... big deal. All this says to me is that you're probably more of a natural leader than a natural follower.

What's relevant to this discussion is the simple observation that mistakes can and do occur. There are several people in this thread saying that the mental math is very easy and that it's all very easy. Your case proves that what they are saying is not an absolute truth. You know what I think is very easy? Reading a number off of a computer screen.

R..

 

[Slamfire]

No Slamfire . . .the fundamental flaw of non-Gradient Factors Buhlmann...

If you read the third quote on post #33 you will notice that AG is referring to the fundamental flaw in GF Buhlmann.

 

[boulderjohn]

I could be wrong, but I'm suspicious because there has been a tendency in the past to want to shield the technique from scrutiny related to decompression accidents. The same is true of RGBM, which was "verified" (as it were) in a similar way, using human guinea pigs in non-controlled environments and blaming computer programmers when divers got bent.

I was told that we know RD is safe to use without change at altitude because no one has gotten bent diving at altitude while using RD.

What about the 6 cases I know of, including a helicopter evacuation?

Well, yes, those happened at altitude, but it was for reasons other than altitude.

What were those reasons?

We don't know. In two cases, the divers made mental errors and miscalculated their decompression. The other cases had to be something else.

How do you know it was not because of altitude? How do you know the one with miscalculations were not exacerbated by altitude?

Because altitude is not a factor in decompression profiles, so it could not have been altitude.

 

[PfcAJ]

I know there have been some statements to that effect and some attempts have been made to devise experiments. I don't know how much progress has been made. If anything I would expect experiments to more clearly define the limitations of the technique than to verify that it can be used interchangeably.

I could be wrong, but I'm suspicious because there has been a tendency in the past to want to shield the technique from scrutiny related to decompression accidents. The same is true of RGBM, which was "verified" (as it were) in a similar way, using human guinea pigs in non-controlled environments and blaming computer programmers when divers got bent.

I'm not a purist about decompression strategies in the least. What works works, but the verification method should be held to as much scrutiny as the results in order for divers to form an intelligent idea of the relative strengths and weaknesses of given approaches. Like I said, I'm skeptical as to whether or not this has begun to happen in any meaningful sense.

All this is to say that your idea of verification and my idea of verification may not be the same. It's a question of definitions. To me a UTD article claiming that they have verified the validity of their pet algorithm is like the butcher certifying his own meat. If we want real verification then UTD should be consulted but in no way responsible for designing the experiment or analyzing the results. It should withstand independent scrutiny.

We're not discussing apples to apples, here. I dont know wtf UTD is trying to peddle, but the GUE ratio deco method produces the same thing that Buhlmann does for a given depth, time, and gas selection. If it doesn't, then its the RD that's wrong, not the algorithm.

 

[Diver0001]

We're not discussing apples to apples, here. I dont know wtf UTD is trying to peddle, but the GUE ratio deco method produces the same thing that Buhlmann does for a given depth, time, and gas selection. If it doesn't, then its the RD that's wrong, not the algorithm.

Says who?

R..

 

[PfcAJ]

Says who?

R..

Uhh, the GUE tech materials? I've taken a few gue classes now, and that's been pretty consistent.

 

[Diver0001]

So GUE says the GUE system is perfect.

O....K....

R..

 

[Kevrumbo]

If you read the third quote on post #33 you will notice that AG is referring to the fundamental flaw in GF Buhlmann.

Actually, in that context -the additional fundamental flaw of Classical Buhlmann is penalizing the use of Helium with extra unnecessary deco time. The original Buhlmann Algorithm did not take into account the greater diffusivity and lesser tissue solubility of inert He compared to N2.

[Bad Internet connection here in Chuuk FSM -trying to keep up reading/posting with the thread]

I've also started last year using a Petrel Computer set to Buhlmann ZHL16 with GF 30/85, and the total deco profile times are similar to RD -except the Petrel has a shallower first deep stop, and also calculates an intermediate Eanx50 segment resulting in an exponential curve rather than an S-Curve as in RD. Again note for the past month here in Truk, I'm mostly using Air bottom mix, and 20/20 Trimix as needed for wreck penetrations in the 50m to 60m depth range; only once used standard 18/45 Trimix (that's $260 for the He alone!) for the deepest wreck in the Lagoon at 67m max.

 

[TSandM]

That's the whole point . . . RD ought to give you almost the same profile as Buhlmann with gradient factors and an oxygen window kludge, because that's how it was derived. It doesn't do that on really extreme dives, but within the boundaries of the "typical" staged decompression activities divers do, it works pretty well. UTD RD has some very deep stops that DON'T show up on a DecoPlanner or Gap profile, which is one of the differences. In addition, the 50% deco on UTD RD is S-shaped, whereas GUE has gone to linear pragmatic. I personally doubt it matters.

I watched the video on the Italian project, and although the details of the experimental protocol aren't discussed, the broad outline of the experimental design seems sound. The one thing that was unclear was whether all divers in the project would dive both profiles, which is very important, as we know there are significant individual differences in the tendency to bubble after dives. The video says the project will take (or has taken; it's unclear to me which) four years, which would suggest a good number of dives, which would be great. Many of the studies in humans suffer from very low numbers, which reduces the power to detect a difference.

 

[PfcAJ]

So GUE says the GUE system is perfect.

O....K....

R..

I'm not sure you understand what GUE is teaching...

If Buhlmann says "do 20mins of deco" for a given dive, the ratio deco result says the same thing. That's hardly groundbreaking or controversial.

A Buhlmann 20/85 ascent schedule works, right? RD produces the exact same thing within its parameters. So....?