What is Ratio Deco?

[rongoodman]

Great to have redundancies and ways to plan a safe way out If everything fails. I just don’t get why not using computers because they may fail. .... There are many more chances of you getting your approximate calculations wrong than a modern computer fail.

There were no "modern computers" at the time ratio deco was being developed. Liquivison was the first, followed by Shearwater, but prior to that they were considered to be unreliable, without the computing power required to run Buhlmann or VPM. Look up the Bakers Dozen article by Jarred Jablonski to see how the computers of the day were regarded.

 

[Belzelbub]

There were no "modern computers" at the time ratio deco was being developed. Liquivison was the first, followed by Shearwater, but prior to that they were considered to be unreliable, without the computing power required to run Buhlmann or VPM. Look up the Bakers Dozen article by Jarred Jablonski to see how the computers of the day were regarded.

That makes sense from a historical perspective, but it doesn’t explain this in the OP.

I had the pleasure of chatting with a UTD instructor yesterday. A very knowledgeable fellow. He said that UTD/GUE divers do not use dive computers. They use a bottom timer and follow a method called "Ratio-Deco."

There have been reliable dive computers for quite some time now. Assuming the UTD Instructor was speaking accurately, why do UTD/GUE divers still not use dive computers?

 

[boulderjohn]

That makes sense from a historical perspective, but it doesn’t explain this in the OP.
There have been reliable dive computers for quite some time now. Assuming the UTD Instructor was speaking accurately, why do UTD/GUE divers still not use dive computers?

It has been quite some time since I was a UTD diver and dived with other UTD divers. To my knowledge, they still prefer to use ratio deco rather than computers.

Their owner, Andrew Georgitis, was originally from GUE, and he was adamantly opposed to the use of computers. (We had discussions about this when I was a UTD diver.) He firmly believed that the ratio deco system in place when I was with them was superior to all other algorithms, so it was not just computer reliability that mattered to him. He believed that a perfectly reliable computer would not be as good as ratio deco because of its inferior algorithm. When I took my ratio deco class from him, every time we worked out a ratio deco profile, another instructor in the room used a laptop to do the same profile using various diving software programs. They were never the same, and since Andrew said ratio deco was the ideal method of computing an ascent, that proved that all other systems were inferior.

That notion was put to rest by the Spisni study a few years ago. Georgitsis sponsored the study and made a video before it started saying it was going to prove the superiority of UTD rato deco, but the exact opposite happened. Since then, they have modified the system, and I don't know much about those changes. I believe that Georgitsis is no longer associated with UTD, so his influence may have waned considerably.

GUE ratio deco and UTD ratio deco had the same start, but they diverged significantly over the years. They were (and I believe still are) deep stop oriented, which is losing favor these days.

 

[jale]

It seems there are different definitions of RD.
For UTD it looks to be an algorithm.
But for others (me included), it is just a mnemotechnic to get your prefered algorithm and to be able to adjust on the fly or at least to give you benchmarks when you plan the dives.

 

[boulderjohn]

It seems there are different definitions of RD.
For UTD it looks to be an algorithm.
But for others (me included), it is just a mnemotechnic to get your prefered algorithm and to be able to adjust on the fly or at least to give you benchmarks when you plan the dives.

When I was with UTD and arguing with both my instructor and Andrew, I was also put in touch with Jarrod Jablonski of GUE, and he helped me compare the two. This was the biggest difference. Right after learning that Andrew thought that the fact that his RD profiles did not match any existing algorithm proved it superiority to all of them; if our RD profile matched an existing algorithm, we had done something wrong. Jarrod said that for GUE, the purpose as to match an existing algorithm; if your RD profile did not reasonably match it, then you had done something wrong.

The other issue which was just then changing was the S-curve. GUE had come up with the S-curve ascent, in which a standard Buhlmann profile was tweaked to make the deeper stops of the middle portion of the ascent (starting at 70 feet) longer than the shallower stops at 40 and 30 feet--very much the opposite of any other algorithm. That was because of a now discarded belief that higher PPO2s during decompression created an "oxygen vacancy" that left "more room" for nitrogen to leave the tissues. I had long argued that this violated Dalton's Law, and Jarrod said that he now believed that, too. He said they were reluctant to change the practice because it had worked in the past. Not long after that, though, they changed that portion of the ascent to a linear profile. (I don't know what they do now.) When I took the RD class from Andrew, he admitted that the "oxygen vacancy" theory was not looking so good, but he came up with two other reasons to keep the S-curve, reasons that I don't remember. I believe the S-curve was still part of the UTD RD system at the time of the Spisni study, but I think they have since taken it out (not sure).

 

[100days-a-year]

So, disproved???