What is Ratio Deco?

[LiteHedded]

Ratio Deco is a curve-fitting exercise. In mathematics, if you have a very complex function that generates a curve or set of curves, it is sometimes possible to approximate the same curve -- through very defined regions -- with a much simpler function. The function that generates the ascent profile in Gap or DecoPlanner or V-planner is not one you can do in your head, at least if you're normal. The math of RD is much simpler, can be done in one's head, and closely approximates the output of V-planner +2, as Bob has mentioned, WITHIN CERTAIN PARAMETERS. It is dependent on some assumptions, those being the use of standard breathing gases and bottom times within what is typical for the depth. For the commonly dived 30 minutes at 150 feet (or 200) it works very well. It diverges more when you are looking at very, very long, relatively shallow dives.

Minimum deco is a way of using a set of mental tables, combined with a standard ascent profile, to manage recreational dives. As it was explained to me, it was derived from playing around with DecoPlanner, and seeing what combinations of depth and time generated a profile that required 1 minute stops from half maximal depth. Again, it is dependent on the use of 32%, and also requires divers who can control an ascent profile fairly precisely. As the majority of the diving world doesn't meet either criterion, Min Deco would not be a very workable approach to decompression for most recreational divers. (And I'm not being condescending -- I know how much work it took before I could reliably execute a precise min deco ascent, especially if I got at all task-loaded.)

IMO it diverges much sooner than you give it credit for.
it works well in the confines of a tech 1 or tech 2 class dive. IE at or under about 30 minutes.
UTD seems to have a unique answer for this divergence, which is to say ratio deco is just right and the algorithm (that this method was devired from) is wrong

 

[Dr. Lecter]

Bad example ... he bent himself like a pretzel because he misapplied RD to the dive he was doing.

That was the point, yeah.

 

[Slamfire]

From this thread a reader can easily tell that there are several flavours of Ratio Deco or Deco on the Fly. I think it is important to highlight differences and their associated philosophies of use.

While they all advocate the use of std gases, std gases for one flavor are not necessarily the same as std gases for other flavors. The flavor that I like the most advocates the use of 21/25 for depths of up to 150'.

UTD trains their students to use Ratio Deco exclusively. As far as I know they are not taught any other way to plan a deco dive. Other flavors tell you that it is only for contingencies, that if results conflict with other established methods ratio deco is wrong for that particular plan. Others say that RD can be a good learning tool to obtain a deeper knowledge about deco diving, but accept that there there could be more convenient ways to plan and execute dives.

After I read and watched all the Ratio Deco material in the Nov 2014 issue of the UTD Journal here, my impression is that UTD is still insisting on their flavor as being the non plus ultra over tables, desktops, PDCs or other deco on the fly flavors.

The preliminary results clearly show massive advantages in implementing s-curves and using UTD’s Ratio Deco over a 30/80 Bulhmann Profile.

UTD hasn't yet provided public access to the data that would support the claim above. I would be very interested in seeing how the study compares to other studies that don't seem to support the purported advantages of the the S-curve and the O2 window.

In fact UTD’s Ratio Deco is the first and still currently the only decompressionstrategy or profile that emphasizes and extends the decompression time at the O2 windows and shortens the time in the intermediate stops.

Why would that be? Is everybody else wrong and UTD the only one in possession of the right answer?

Then in the late 90’s Erik Baker released his Deco Software which allowed us to implement the “Work-man” adjustments (gradient factor HI and gradient factor LO) to a Bulhmann profile. This allowed us to push the Bulhmann stops much deeper in the computer-generated profiles, however the consequence, or penalty, was additional unnecessary decompression time – fundamental flaw in the Bulhmann model.

So somehow slow tissues will pause their ongasing while you do the S-curve with an extended O2 window? Trying to account for that additional ongasing is a "fundamental flaw"?

Despite its name this publication is no scientific journal. The way their communication around ratio deco is structured resembles more that of an infomercial: a) Present the problem b) Present the solution and all the wonderful emotional "facts" that back said solution c) make the sale:

To take the Ratio Deco online course, CLICK HERE.

 

[Kevrumbo]

It's a method that's only really reliable within a relatively short range of exposures and, as a certain mouthy Truk diving SB denizen can attest, a great way to bend yourself like a pretzel if you do the math wrong on ascent. It also requires standard gasses. Overall, it's good to know as a back-pocket resource and as a sanity check on plans, but it's not a universally applicable Jedi mind trick for deco.

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. [Karma is coming for you Dr. Lecter and your own "mouthy". . .]

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

http://www.scubaboard.com/forums/di...p-vein-thrombosis-status-post-dcs-type-i.html

Been in Truk every year since then --now for 4 weeks since Oct, and no problems with Ratio Deco --even with non-standadard gases like 20/20 Air Bottom Mix, 50% and 100% O2 for deco.

The issue with the supposed residual "on-gassing" criticism of doing S-Curves starting at 21m Eanx50 deco stop is a concern if coming off high FN2 mixes such as Air. I now compensate with more time at 9m on Eanx50 and 6m on O2.

 

[Dr. Lecter]

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. [Karma is coming for you Dr. Lecter and your own "mouthy". . .]

http://www.scubaboard.com/forums/near-misses-lessons-learned/264517-type-i-bends-hit-chuuk.html

http://www.scubaboard.com/forums/di...p-vein-thrombosis-status-post-dcs-type-i.html

Been in Truk every year since then --now for 4 weeks since Oct, and no problems with Ratio Deco --even with non-standadard gases like 20/20 Air Bottom Mix, 50% and 100% O2 for deco.

The issue with the supposed residual "on-gassing" criticism of doing S-Curves starting at 21m Eanx50 deco stop is a concern if coming off high FN2 mixes such as Air. I now compensate with more time at 9m on Eanx50 and 6m on O2.

Touchy touchy, kiddo. The point isn't that you're forever marked because you made a mistake, the point is that ability to miscalculate as you did is something uniquely inherent to RD. Its virtues are flexibility that tables can't match unless you run a bunch of them for contingencies, and the reliability of your brain versus your DC (and this one cuts both ways). We pays our monies and we takes our chances.

As for karma, it comes in its own good time. Like most people who spend a lot of days every year diving deep for a long time and then hanging for a lot longer, I've had my niggles along the way as I settled into an approach that has (knock on wood) worked well for me. One day I may have more, or worse. But whatever the cause, it won't be from relying on my brain alone to calculate an ascent profile on the fly.

 

[TSandM]

I thought it was fabulous that UTD was involved in a research project to compare RD with other decompression strategies, but I was disappointed, when I watched the video, to discover that they are comparing the two in an area where the curve-fitting is excellent. This results in VERY similar profiles, with the exception of the very deep stops (one of the things I seriously wonder about) and the S-curve shaping in the 50% segment, which I doubt makes any real difference at all. But I guess we will see. It appears that reputable hyperbaric scientists are involved in the project, and they are gathering a LOT of data, not just Doppler studies. The results may be a fascinating look into decompression physiology, even if they show no real difference in clinical outcome in the end.

 

[Slamfire]

The issue with the supposed residual "on-gassing" criticism of doing S-Curves starting at 21m Eanx50 deco stop is a concern if coming off high FN2 mixes such as Air. I now compensate with more time at 9m on Eanx50 and 6m on O2.

You compensated by extending shallower stops, which was described as a "fundamental flaw" of Buhlmann. And it is not only limited to the O2 window extension at the 70' gas switch -- UTD Ratio Deco prescribes deeper deep stops than most while claiming no shallow stop penalizing and in spite of studies casting doubt on the benefit of beginning your stops so deep.

My impression is that there is a pattern of selectively acting on certain observations and ignoring others because those do not conform to the pre-existing bias. Altitude is irrelevant, thus a hit at altitude must be due to other factors. Helium is insoluble, therefore we can ignore helium. And since helium is ignorable then you shouldn't be penalized for very deep stops on helium with low N2 concentrations.

Oversimplification of a very complex situation with the proclamation of it being better than anything else out there without having any solid analytical grunt work behind it.

 

[PfcAJ]

I thought it was fabulous that UTD was involved in a research project to compare RD with other decompression strategies, but I was disappointed, when I watched the video, to discover that they are comparing the two in an area where the curve-fitting is excellent. This results in VERY similar profiles, with the exception of the very deep stops (one of the things I seriously wonder about) and the S-curve shaping in the 50% segment, which I doubt makes any real difference at all. But I guess we will see. It appears that reputable hyperbaric scientists are involved in the project, and they are gathering a LOT of data, not just Doppler studies. The results may be a fascinating look into decompression physiology, even if they show no real difference in clinical outcome in the end.

The s-curve vs linear thing is tiddlywinks imo. Its a few minutes difference here and there.

 

[Kevrumbo]

Touchy touchy, kiddo. The point isn't that you're forever marked because you made a mistake, the point is that ability to miscalculate as you did is something uniquely inherent to RD. Its virtues are flexibility that tables can't match unless you run a bunch of them for contingencies, and the reliability of your brain versus your DC (and this one cuts both ways). We pays our monies and we takes our chances.

As for karma, it comes in its own good time. Like most people who spend a lot of days every year diving deep for a long time and then hanging for a lot longer, I've had my niggles along the way as I settled into an approach that has (knock on wood) worked well for me. One day I may have more, or worse. But whatever the cause, it won't be from relying on my brain alone to calculate an ascent profile on the fly.

Then may you never have the misfortune of suffering acute DCS in an overseas remote location -and perhaps use some of your brain power to memorize an In-Water-Recompression Profile to quickly treat a type I episode (the most likely DCS variant that may arise even in a correctly followed & completed decompression profile).

__

You compensated by extending shallower stops, which was described as a "fundamental flaw" of Buhlmann. And it is not only limited to the O2 window extension at the 70' gas switch -- UTD Ratio Deco prescribes deeper deep stops than most while claiming no shallow stop penalizing and in spite of studies casting doubt on the benefit of beginning your stops so deep.

My impression is that there is a pattern of selectively acting on certain observations and ignoring others because those do not conform to the pre-existing bias. Altitude is irrelevant, thus a hit at altitude must be due to other factors. Helium is insoluble, therefore we can ignore helium. And since helium is ignorable then you shouldn't be penalized for very deep stops on helium with low N2 concentrations.

Oversimplification of a very complex situation with the proclamation of it being better than anything else out there without having any solid analytical grunt work behind it.

No Slamfire . . .the fundamental flaw of non-Gradient Factors Buhlmann is pushing tissue tensions to the M-Value curve -the maximum tolerable depth v. time curve without theoretical bubble precipitation/formation. Ratio Deco has similar run times to Buhlmann ZHL-16 with 30/85 Gradient Factors, but the depth versus time deco profile curve is shaped differently by the application of Deep Stops starting at 75% of max depth, and use of the S-Curve for the Eanx50 deco segment starting at 21m.

The problem with Deep Stops and the S-Curve in Ratio Deco is when applying it with non-standard gases like Air. The high FN2 and inert N2 solubility of Air Bottom Mix (79%) versus Standard Bottom Gas 18/45 Trimix (37%) for example, may hold longer in residual tissue super-saturation resulting in potential Boyle Expansion Bubble(s) formation -in turn precipitating the "niggles", or worse, frank & acute DCS type I Symptoms- when performing the S-Curve profile --i.e. Spending extra time on Eanx50 at 21m & 18m to take advantage of the high PPO2 Oxygen Window/Inert Concentration Gradient, and then pushing the ambient pressure gradient by ascending to further off-gas inerts by shorter stop times at 15m & 12m. . .

I compensate on my Deep Air dives here in Truk with "straightening" the S-Curve a little more linearly (roughly same stop times for the 21m to 9m segment), and extending the O2 stop at 6m another 10 to 20min beyond the calculated RD schedule, with a final slow 1m/min ascent rate to the surface.

 

[Dr. Lecter]

and perhaps use some of your brain power to memorize an In-Water-Recompression Profile to quickly treat a type I episode.

BT, DT. To be clear, I wouldn't wish the kind of bone pain I associate with even relatively mild type I issues on my worst enemy. It's nasty stuff and I can only imagine how much worse a significant hit would be.