Modern Ratio Deco usage?

[boulderjohn]

I was trained in the UTD version of RD. I learned it unofficially through my regular UTD instructor and used it for years before taking the "official" class from Andrew Georgitsis. I had taken the first half of it immediately after the formation of UTD during a webinar with Andrew, but the second half fell through. I never got my "official" RD card because I dropped out of UTD soon after taking the "official" class.

Here are some scattered comments from my experiences using it.

Unlike GUE, UTD teaches RD as the primary tool for planning dives. According to a private exchange I had with Jarrod Jablonski of GUE, GUE's philosophy is that RD must match the profile that would have been created by specific deco software, but UTD does precisely the opposite. When I took the "official" class, Andrew would show us how to plan a dive with RD, and as he did, our instructor (who was also present) would plan the dives using different software programs. In each case, the results would be different, sometimes very different. Andrew would then use that difference to show why you should not use computers or desktop software. Since RD was assumed to be perfect, those differences showed how wrong the commercial algorithms (all of them) were. The course materials emphasized this, showing on graphs the difference between a commercial algorithm profile and a "proper" RD profile.

In the aforementioned webinar, one of the participants asked Andrew how he knew RD worked, and he said "You have to have faith." "Faith in you?" she asked. "Yes," he answered.

UTD also teaches that RD can be used at any altitude without change. In the aforementioned private exchange, Jarrod Jablonski told me that RD was created at sea level and could not be used at altitude. He said it was obvious that altitude made a difference, but they had never made any kinds of adjustments for altitude so he did not recommend using it there. When I asked Andrew how he knew it could be used without change at altitude, he said that he used it without any adjustments while diving at lake Tahoe, and he was fine, so therefore it would be fine for anyone.

Andrew also said that no one had ever been bent while using RD at altitude. I said we had had a whole bunch of people bent just in our group diving in New Mexico at 4,600 feet. He said those did not count because those cases of DCS had been caused by something other than using RD altitude. What caused them? He didn't know. Then how did he know that they were not related to altitude? Because altitude is not a factor in decompression, so it had to be something else. He didn't know what, but it could not have been using RD at altitude.

Although Jarrod Jablonski told me that GUE does not approve of the use of RD at altitude, the only GUE instructor I know personally who dives at altitude teaches his students that altitude does not matter for decompression.

When I mentioned the cases of DCS in our group while using RD in a ScubaBoard thread, I received a threatening email from UTD. I was told that mentioning the DCS cases using RD in our dive group was considered to be disparaging of UTD. I am a PADI instructor, and PADI standards do not allow members to disparage other agencies. If I were to mention those cases again, I would be reported to PADI and could face suspension or expulsion. That is when I dropped my UTD membership.

I spend two months diving in South Florida. Although I use a couple different dive operators while there, almost all of my deco diving has been with an operation that is a GUE instructor development center. There staff members often dive with us, and I don't remember ever seeing one of them who was not using a computer.

 

[lowviz]

That was a ballsy and enlightening post.

I don't get their stress over the altitude part, though. GUE/UTD types love to do math in their heads. RD (to me) appears to be a stops pattern that gets adjusted with time and depth.

Why not just adjust the depths by the ratio of ambient atmospheric pressure over 760 mm Hg? All your stops become increasingly shallower with increasing elevation, same pattern.

 

[boulderjohn]

Here is something I intended to include in that last post but forgot.

If you go to the technical diving forum and read the threads on deep stops, you will see that there is a lot of controversy there, but you will also see that the current research is moving against deep stops. To give you an idea of the degree to which it is true, the existing PADI trimix curriculum currently requires instruction and practice in using deep stops, but in its latest training bulletin, PADI freed instructors from that requirement because of that trend in the research. We who teach trimix are no longer required to have students use deep stops on any dives.

You will also see that the definition of "deep stops" is very much in question. How deep is deep? The most fervid supporter of deep stops in those threads, Ross Hemingway, told me in a private email exchange (which was, BTW, more contentious than the thread) that he thinks deep stops as he defines them are valuable. He says the problem began with how some people used and advocated them--specifically the DIR people and Ratio Deco. He said they pushed it to an extreme that was indeed harmful.

How different is it?

I now use Buhlmann with the gradient factors recommended by Dr. Simon Mitchell--50/80. I just ran a simple dive profile using it, and it calls for my first stop at 90 feet. If I were using RD, my first stop would be at 150 feet.

 

[boulderjohn]

Starting the thread out, one of my mentors taught me the basics and he has successfully used it for years as well as a sanity check his dive computer

How does this sanity check work?

I was recently in a situation where I was doing a deco dive with someone and we were joined by someone I had dived with a number of times in the distant past. During the interim, he had gotten GUE training and done his diving with Ratio Deco. He had decided, though, that he wanted to get with the current trend of using Buhlmann and Gradient Factors, which is what the other diver and I were using. To that end, he had purchased a Shearwater computer, and he was using it with us for the first time on a dive.

We planned the dive using Multi-deco with 40/80 gradient factors, and we wrote the plan and two contingencies in our slates. We agreed to use the slates as backups and use the computers as our primaries. It was not a really big dive, and when we started our ascents, the computers had the first stop at 60 feet. (The multi-deco plan had the first stop at 70 feet, but our actual dive was not as deep as planned.) The three of us started the ascent together, but the other guy suddenly stopped. Throughout our deco, he stayed well below us. When he was done, he said that when he saw the computer telling him to ascend to 60 feet, he knew it had to be wrong because he had been trained that the first stop had to be much, much deeper than that. He used the word "insane" to describe the 60 foot first stop depth that we all had and which was essentially what we had preplanned for the dive using Multi-deco. He did not explain why he had not noticed that insanity prior to the dive.

So, if you are using it for a "sanity check" for the computer and notice a big difference like that, how do you know which one is insane?

 

[PfcAJ]

How does this sanity check work?

I was recently in a situation where I was doing a deco dive with someone and we were joined by someone I had dived with a number of times in the distant past. During the interim, he had gotten GUE training and done his diving with Ratio Deco. He had decided, though, that he wanted to get with the current trend of using Buhlmann and Gradient Factors, which is what the other diver and I were using. To that end, he had purchased a Shearwater computer, and he was using it with us for the first time on a dive.

We planned the dive using Multi-deco with 40/80 gradient factors, and we wrote the plan and two contingencies in our slates. We agreed to use the slates as backups and use the computers as our primaries. It was not a really big dive, and when we started our ascents, the computers had the first stop at 60 feet. (The multi-deco plan had the first stop at 70 feet, but our actual dive was not as deep as planned.) The three of us started the ascent together, but the other guy suddenly stopped. Throughout our deco, he stayed well below us. When he was done, he said that when he saw the computer telling him to ascend to 60 feet, he knew it had to be wrong because he had been trained that the first stop had to be much, much deeper than that. He used the word "insane" to describe the 60 foot first stop depth that we all had and which was essentially what we had preplanned for the dive using Multi-deco. He did not explain why he had not noticed that insanity prior to the dive.

So, if you are using it for a "sanity check" for the computer and notice a big difference like that, how do you know which one is insane?

How deep did he want to stop? How deep was the dive? Time?

 

[KevinNM]

I'm told that once upon a time GUE believed in bubble models more and had a first stop at 75% of max. That isn't current per modern GUE SOP.

 

[PfcAJ]

Here is something I intended to include in that last post but forgot.

If you go to the technical diving forum and read the threads on deep stops, you will see that there is a lot of controversy there, but you will also see that the current research is moving against deep stops. To give you an idea of the degree to which it is true, the existing PADI trimix curriculum currently requires instruction and practice in using deep stops, but in its latest training bulletin, PADI freed instructors from that requirement because of that trend in the research. We who teach trimix are no longer required to have students use deep stops on any dives.

You will also see that the definition of "deep stops" is very much in question. How deep is deep? The most fervid supporter of deep stops in those threads, Ross Hemingway, told me in a private email exchange (which was, BTW, more contentious than the thread) that he thinks deep stops as he defines them are valuable. He says the problem began with how some people used and advocated them--specifically the DIR people and Ratio Deco. He said they pushed it to an extreme that was indeed harmful.

How different is it?

I now use Buhlmann with the gradient factors recommended by Dr. Simon Mitchell--50/80. I just ran a simple dive profile using it, and it calls for my first stop at 90 feet. If I were using RD, my first stop would be at 150 feet.

Looking at a fairly normal 200ft dive (30mins, 18/45) a 20/85 schedule stops you at 120', with 9mins between 120 and 70. 30fpm from 200ft to 120ft takes 2.6mins

RD (as GUE teaches it) would stop you at 150ft with 11mins between 150 and 70, with a 30fpm ascent to 150' (1.6mins).

So its literally 3min difference between RD and what decoplanner spits out.

I think if I can get within 3mins that its pretty good. You can fiddle with your GF settings and get more than 3mins difference.

Now, if that time spent deeper is a good use of time is a topic for another thread But as far as approximating 20/85, it does a darn good job.

 

[PfcAJ]

I'm told that once upon a time GUE believed in bubble models more and had a first stop at 75% of max. That isn't current per modern GUE SOP.

All my course materials (which might be a bit out of date) had 75% of avg.

 

[stuartv]

as far as approximating 20/85, it does a darn good job.

You say that like it's a good thing.

boulderjohn said he uses 50/80 and was using 40/80 for the planning on the dive he was talking about. Simon Mitchell says he uses 50/80.

I have yet to see anyone make a solid case that 50/80 is any better of a choice than 80/80, and I have personally specifically asked a couple of well-respected technical diving authorities that specific question. 20/85 definitely seems like it would be stopping you too deep and spending too much time down there - based on the modern science that has been getting published recently.

I mean, if you are okay with hitting the surface with a GF99 of 80, then why are you not okay with having a GF99 of 80 at 60' depth (or any other depth)? What is it about deco theory, in your mind, that leads you to conclude that limiting yourself to a GF99 of 20 for the initial part of your ascent is safer? If a GF99 of 80 is safe on the surface, why is it not safe at depth? The last part of your ascent is the most hazardous, right? If you can do that part of the ascent with a GF99 that is ramping up from, say, 70 to 80 as you go, why is it any more of a problem to go from 70 to 80 during a deeper part of the ascent, where the pressure gradient is actually changing more slowly?

As for use of RD, I personally would not trust myself to do any math underwater that I can avoid - say, by carrying 2 computers. I plan my dive ahead of time using Multi Deco and I know getting in what my worst case scenario is for deco, so if both my computers died, well, first of all, I wouldn't have a depth gauge or timer. But, I could do something makeshift if I had to, for that. And I would know pretty closely what my deco stops should be just from planning them ahead and writing them down. Relying on RD seems inherently less safe than how I do it now.

Relying on being able to do math after potentially being narced (where science seems to have shown that the effects linger, even after ascending) seems less safe than relying on a computer to do the math for you.

If you're willing to rely on an electronic device to calculate your average depth for you, what possible reason could you have for not being willing to let it calculate your deco stops for you? Does anyone think that computers retain their ability to calculate easy stuff, like average depth, but lose their ability to calculate a deco stop?

If you rely on a mechanical depth gauge, a mechanical timer, with redundancy for both, and you ascend based on a plan worked out in advance based on max depth and bottom time, more power to you. I'll grant you that that may be safer than simply using 2 computers (from 2 different companies, so they are proof against having a bug in common) - unless, of course, your actual dive ends up varying significantly from your plan. But, if you use an electronic device for any of that and you are telling yourself that it's safer to calculate your deco in your head, after being at depth, no less, than to let that electronic device calculate it for you, well, I don't follow your logic.

 

[Captain Swoop]

I was trained in the UTD version of RD. I learned it unofficially through my regular UTD instructor and used it for years before taking the "official" class from Andrew Georgitsis. I had taken the first half of it immediately after the formation of UTD during a webinar with Andrew, but the second half fell through. I never got my "official" RD card because I dropped out of UTD soon after taking the "official" class.

Here are some scattered comments from my experiences using it.

Unlike GUE, UTD teaches RD as the primary tool for planning dives. According to a private exchange I had with Jarrod Jablonski of GUE, GUE's philosophy is that RD must match the profile that would have been created by specific deco software, but UTD does precisely the opposite. When I took the "official" class, Andrew would show us how to plan a dive with RD, and as he did, our instructor (who was also present) would plan the dives using different software programs. In each case, the results would be different, sometimes very different. Andrew would then use that difference to show why you should not use computers or desktop software. Since RD was assumed to be perfect, those differences showed how wrong the commercial algorithms (all of them) were. The course materials emphasized this, showing on graphs the difference between a commercial algorithm profile and a "proper" RD profile.

In the aforementioned webinar, one of the participants asked Andrew how he knew RD worked, and he said "You have to have faith." "Faith in you?" she asked. "Yes," he answered.

UTD also teaches that RD can be used at any altitude without change. In the aforementioned private exchange, Jarrod Jablonski told me that RD was created at sea level and could not be used at altitude. He said it was obvious that altitude made a difference, but they had never made any kinds of adjustments for altitude so he did not recommend using it there. When I asked Andrew how he knew it could be used without change at altitude, he said that he used it without any adjustments while diving at lake Tahoe, and he was fine, so therefore it would be fine for anyone.

Andrew also said that no one had ever been bent while using RD at altitude. I said we had had a whole bunch of people bent just in our group diving in New Mexico at 4,600 feet. He said those did not count because those cases of DCS had been caused by something other than using RD altitude. What caused them? He didn't know. Then how did he know that they were not related to altitude? Because altitude is not a factor in decompression, so it had to be something else. He didn't know what, but it could not have been using RD at altitude.

It almost comes across as a cult!