Which decompression algo does GUE use?

[WhiteSands]

Is it VPM? Thanks.

 

[Diver0001]

GUE teaches ratio-deco. Ratio deco isn't a model, it's a method for on-the-fly determination of deco needs that fits the results of several models.

R..

 

[rivers]

According to my rec 3 materials, the tables are cut using 20/85 GF using GUE's decoplanner. I can't comment on anything besides rec 3 however.

 

[WhiteSands]

According to my rec 3 materials, the tables are cut using 20/85 GF using GUE's decoplanner. I can't comment on anything besides rec 3 however.

Hi Rivers,
Thanks for the feedback. I assume GF refers to Gradient Factors by Erik Baker?

I would like to learn how do the different algos like RGBM, VPM and GF compare to each other in real world use. Is there a good resource where I can read up more on this?

---------- Post added May 27th, 2014 at 09:02 AM ----------

GUE teaches ratio-deco. Ratio deco isn't a model, it's a method for on-the-fly determination of deco needs that fits the results of several models.

R..

Hmm..I think its UTD that uses ratio deco exclusively, because that's what I have been taught.

I heard GUE divers use an excel spreadsheet called a decoplanner, and I'd like to learn which algo it is based on.
If I am not mistaken, ratio deco is a shortcut derived from what you get from decoplanner.

If anyone has information on why GUE chose to base their diving on GF, please enlighten me, thanks.

 

[PfcAJ]

Deco planner has buhlmann and vpm algorithms. You can toggle back and forth and compare the two.

---------- Post added May 26th, 2014 at 09:09 PM ----------

Ratio deco is just a simple tool that describes patterns outputted by the deco algorithm of your choice. It works fairly well for 20-30min bottom times, but breaks down much past that and ends up being really aggressive.

For instance, at x depth with y gases, there might be a 1:1ratio between bottom time and deco time. At another depth with different gases, it might be 1:2.

Ratio deco is not taught as a stand alone thing. Its
just a trick to help adjust your deco if the plan is say a little deeper or shallower, or a little longer or shorter, or a combo of those conditions. It's handy.

 

[boulderjohn]

Ratio deco is just a simple tool that describes patterns outputted by the deco algorithm of your choice. It works fairly well for 20-30min bottom times, but breaks down much past that and ends up being really aggressive.

For instance, at x depth with y gases, there might be a 1:1ratio between bottom time and deco time. At another depth with different gases, it might be 1:2.

Ratio deco is not taught as a stand alone thing. Its just a trick to help adjust your deco if the plan is say a little deeper or shallower, or a little longer or shorter, or a combo of those conditions. It's handy.

I had an excellent online conversation with Jarrod Jablonski, the leader of GUE, on this topic, and what he said conforms precisely to what PfcAJ said. It is possible to confuse GUE policies with the policies of a different organization, UTD, that also uses the term DIR to describe its approach. That organization uses Ratio Deco for all dive planning. No other programming is used. Their version of Ratio Deco is also somewhat different from GUE's. It is important to recognize the different approaches.

 

[TSandM]

Pure Buhlmann is a dissolved gas model . . . it assumes that all gas is dissolved, and diffusing back and forth from the compartments to the blood and lungs, and into the exhaled air. Pure dissolved gas models tend to push you very shallow very fast, and then hold you there for a long time while you offgas. However, we know from Doppler studies that not all gas is dissolved. Gas will form bubbles if the ambient pressure drops enough, and bubbles have fairly different dynamics in terms of exchange their contents with the dissolved gases in the blood surrounding them. VPM is a bubble model, and those models tend to start stops deeper and use a more gradual curve. Adjusting the gradient factors on a Buhlmann model has the effect of creating a shape more like a bubble model. GF low tells you where the offgassing point is, and where you will start your deeper stops. GF high tells you how close to the M-value you can run.

WhiteSands, you have a lot of curiosity about this stuff and you ask a lot of questions, which is fantastic. Most of your questions can be answered by a careful reading of Mark Powell's book, Deco for Divers. In addition, look up Erik Baker's paper, "Understanding M-values", which is available in multiple sites on the net. And finally, if this stuff really grabs you (as it did me), purchase GUE's DVD, "The Mysterious Malady". You need the latter to understand how much uncertainty there is in ANYTHING your read about decompression models or algorithms.

 

[LiteHedded]

they teach pragmatic deco that you derive from decoplanner. buhlmann 20/85 or vpm.
they also teach ratio deco that comes from 20/85 buhlmann and works sometimes but that can be dangerous on other dives

there is some growing concern that vpm is bending people so they're stressing bulmann in the classes. as I understand it the gradient factors were chosen based on dives done at wakulla over the years (tweaked later a bit to match what the popular new vpm algorithm was spitting out)

 

[rivers]

Hi Rivers,
Thanks for the feedback. I assume GF refers to Gradient Factors by Erik Baker?

I would like to learn how do the different algos like RGBM, VPM and GF compare to each other in real world use. Is there a good resource where I can read up more on this?

As others have mentioned, Mark Powell's Deco for Divers is an excellent resource for explaining the different deco algorithms. I haven't used decoplanner, so I can't comment on how it works, etc. but, I have played around with baltic deco and multideco. With both programs, you can use VPM or GF and play around with how conservative or aggressive you want a particular dive profile.

 

[WhiteSands]

Deco planner has buhlmann and vpm algorithms. You can toggle back and forth and compare the two.

---------- Post added May 26th, 2014 at 09:09 PM ----------

Ratio deco is just a simple tool that describes patterns outputted by the deco algorithm of your choice. It works fairly well for 20-30min bottom times, but breaks down much past that and ends up being really aggressive.

For instance, at x depth with y gases, there might be a 1:1ratio between bottom time and deco time. At another depth with different gases, it might be 1:2.

Ratio deco is not taught as a stand alone thing. Its
just a trick to help adjust your deco if the plan is say a little deeper or shallower, or a little longer or shorter, or a combo of those conditions. It's handy.

I agree. I also feel that taking a tool meant to be a handy heuristic (i.e. ratio deco) and using it to plan dives exclusively is...err....a bit worrying to me. Especially when it stops working at extremes of the range.

There seems to be an emphasis on simplification over precision in the UTD philosophy. I think that's great for things that don't really matter, but for calculating deco schedules and things like rock bottom, I'm not really comfortable with over simplification.

---------- Post added May 28th, 2014 at 09:09 AM ----------

Pure Buhlmann is a dissolved gas model . . . it assumes that all gas is dissolved, and diffusing back and forth from the compartments to the blood and lungs, and into the exhaled air. Pure dissolved gas models tend to push you very shallow very fast, and then hold you there for a long time while you offgas. However, we know from Doppler studies that not all gas is dissolved. Gas will form bubbles if the ambient pressure drops enough, and bubbles have fairly different dynamics in terms of exchange their contents with the dissolved gases in the blood surrounding them.

Thanks for the references to the reading materials, it's just what I was looking for.

I'm still a bit confused as to how Baker's work relates to Buhlmann's work. Is Baker's work derived from Buhlmann?

I was introduced to the various gas models in UTD class. Buhlmann's model in particular was knocked on pretty often. E.g. we were taught that his assumptions that gasses stayed dissolved at depth was wrong, that he assumed similar rates for on-gassing and off-gassing, which was incorrect. So I am a bit surprised to learn that deco planner still refers to Buhlmann's model as a reference? I was given the impression it was obsolete and unsafe to follow, because it does not take into account getting rid of bubbles at depth before ascending.

From what little research I have done, I have read of VPM bending people also. It seems RGBM has 100k trials of real dives with no reported bends (according to the creator who posted on Scubaboard some time back), and the model can be safely extrapolated, within limits.

My knowledge in this area is very limited, but I am just curious why GUE has not adopted RGBM as the deco model of choice. Can anyone explain?