Can someone explain Ratio Decompression?

[rjack321]

While all decompression models are based upon ratios, the term "ratio decompression" is most associated with the concept of "deco on the fly" as provided by previous posters.

"on the fly" is anywhere from at home beforehand, on the boat, or during the ascent. People use it differently depending on what & when they were taught and how comfortable they are with the deco & dive as a whole.

 

[Slamfire]

Hmmm where did you come up with this concept?

I did not come up with it. It's already been done. If you click on the link I provided in my post, you will see an article detailing it.

RD is an algorithm with a finite number of steps, which solves the practical problem in a recursive manner, just like Buhlmann's more complicated mathematical algorithm or VPM.

Then allow me to explain what I was referring to when saying it is not an algorithm. Ratio Deco was not developed getting goats bent in a chamber. There were no statistical human trials used for developing RD. There are no bubble theories directly involved involved in its development. There are no multiple tissues, etc. The development of RD simply consisted in detecting patterns in other previously established algorithms.

I think I could come up with a total time & schedule for pretty much any plausible depth/time/gas combo off the top of my head from first principles and that it would fall somewhere within the nominal to +5 range with VPM (which is about the size of the state of Delaware so its not very a difficult task).

Again, if you read the article I referenced, you will see the author limits the conservatism to only nominal. He says, "So let’s look again at our v-planner example. Frankly, we could have used any algorithm – US Navy, Buhlmann, DCIEM, Ben & Jerry’s, it really makes no difference. You be the judge. I use VPM and v-planner as previously stated because it works nicely.

If you want to run the profile yourself, please note a couple of things… I set the conservatism to zero or actually “Nominal.” This may not be the way you or I would choose to dive but it does show us the “pure” algorithm… more or less… so it’s where we start."

 

[rjack321]

I did not come up with it. It's already been done. If you click on the link I provided in my post, you will see an article detailing it.

Then allow me to explain what I was referring to when saying it is not an algorithm. Ratio Deco was not developed getting goats bent in a chamber. There were no statistical human trials used for developing RD. There are no bubble theories directly involved involved in its development. There are no multiple tissues, etc. The development of RD simply consisted in detecting patterns in other previously established algorithms.

Again, if you read the article I referenced, you will see the author limits the conservatism to only nominal. He says, "So let’s look again at our v-planner example. Frankly, we could have used any algorithm – US Navy, Buhlmann, DCIEM, Ben & Jerry’s, it really makes no difference. You be the judge. I use VPM and v-planner as previously stated because it works nicely.

If you want to run the profile yourself, please note a couple of things… I set the conservatism to zero or actually “Nominal.” This may not be the way you or I would choose to dive but it does show us the “pure” algorithm… more or less… so it’s where we start."

I have read Doppler's article, I have no issues with it apart from the fact that its rather generic, and its hard for even a moderately experienced deco diver to take away an actual plan to utilize. From your post, I can't tell if you actually understand AG/GUE's/UTD's version or not. But for one thing the shape will be completely different from a Buhlmann or VPM profile due to bubble theory as first described by Brian Hill et al. Do you have any practical experience to add with ratio deco or are you just attempting to slam GUE/UTD etc people who use it?

 

[Blackwood]

Rather than invite an argument about the semantics of the word algorithm, I find it's easier to say that ratio decompression envelopes other 'classical decompression algorithms.'

Is it an algorithm by definition? I suppose maybe, but it can't solve 'every' problem in what I'll call Proper Noun format (i.e. published "Ratio Decompression" as opposed to, say, Kevin's form of ratio decompression). I can't for example plug in a non-standard gas (like 80% instead of 50%) and get the right answer without going outside the scope of the system. Buhlmann, VPM, the Really Good Bends Model, etc. use rigorous math to solve for (practically) all inputs.

 

[AndyNZ]

IBut for one thing the shape will be completely different from a Buhlmann or VPM profile due to bubble theory as first described by Brian Hill et al.

Isn't kinda the point, though? For the same dive, with the same gasses, different planning tools will give you different profiles - all of which have some empirical evidence to say that they are "reasonable" in terms of not getting bent. All RD is, to my mind, is to put a line through the envelope using simple guidelines.

 

[rjack321]

Rather than invite an argument about the semantics of the word algorithm, I find it's easier to say that ratio decompression envelopes other 'classical decompression algorithms.'

Is it an algorithm by definition? I suppose maybe, but it can't solve 'every' problem in what I'll call Proper Noun format (i.e. published "Ratio Decompression" as opposed to, say, Kevin's form of ratio decompression). I can't for example plug in a non-standard gas (like 80% instead of 50%) and get the right answer without going outside to scope of the system. Buhlmann, VPM, the Really Good Bends Model, etc. use rigorous math to solve for (practically) any inputs.

Yes those models very precisely solve any gas/time/depth mix.

But if you play with the GFs in Buhlmann or the conservatism in V-planner you get a feeling for how wildly the accuracy can vary (for a 25min 150ft dive, by about 15mins of deco or >50% differences in time).

Precision = the ability to consistently reproduce an answer
Accuracy = the degree of closeness to the "true value"

Since the "true value" for any decompression dive is subject to the vagueries of physiology and barely predictable, very precise answers aren't all that much more practically useful than less precise answers.

RD would be an attempt to provide practical answers, and its expected that personal accuracy can improve through trial and error (aka experience) over time. Vs. the more math oriented algorithms for which (for instance) Ross is trying to build a statistical database of clinical and subclinical hits to be able to refine V-planner.

 

[Kevrumbo]

Rather than invite an argument about the semantics of the word algorithm, I find it's easier to say that ratio decompression envelopes other 'classical decompression algorithms.'

Is it an algorithm by definition? I suppose maybe, but it can't solve 'every' problem in what I'll call Proper Noun format (i.e. published "Ratio Decompression" as opposed to, say, Kevin's form of ratio decompression). I can't for example plug in a non-standard gas (like 80% instead of 50%) and get the right answer without going outside the scope of the system. Buhlmann, VPM, the Really Good Bends Model, etc. use rigorous math to solve for (practically) all inputs.

Examine and inspect the basic four operator arithmetic (addition, subtraction, multiplication & division) behind the Ratio Deco Method. If you can write a program for it and its solutions --it is by implication algorithmic in nature. . .

 

[rjack321]

Isn't kinda the point, though? For the same dive, with the same gasses, different planning tools will give you different profiles - all of which have some empirical evidence to say that they are "reasonable" in terms of not getting bent. All RD is, to my mind, is to put a line through the envelope using simple guidelines.

They give you similar answers, not surpisingly. Something that genuinely doesn't work is not going to survive.

 

[Blackwood]

If you can write a program for it and its solutions --it is by implication algorithmic in nature. . .

Correct, but there remains the caveat that it only works with a limited number of inputs.

Without doing a bunch of homework and establishing my own set point and ratio, I can't for example solve for a dive to 140 feet breathing 15/55 and using EAN80 at 30 feet for decompression.

 

[Blackwood]

Precision = the ability to consistently reproduce an answer
Accuracy = the degree of closeness to the "true value"

Since the "true value" for any decompression dive is subject to the vagueries of physiology and barely predictable, very precise answers aren't all that much more practically useful than less precise answers.

Funny you should mention that. I was just considering editing my post to change "the right answer" to "a right answer"