My Journey into UTD Ratio Deco

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You can adjust the GFHigh on Shearwater during the dive. Effectively adjusting for unexpected circumstances such as cold and workload.

You could also just watch the GF99 display and keep it below your new self imposed threshold.
 
1) Depth averaging: I do this like Hu Porter, I don't try and remember 6 or 7 different depths and compute an average at the end. I keep a rolling average in my head, "if I had to ascent right now what depth would I use?" If the next five mins ends up deeper than that depth the average slides down, if the next 5 mins is shallower the average slides up. Near the end of the dive, initial ascent-ish, I look back over the profile in my head and decide whether I have been shallowing or deepening and if there is an element of reverse profiling in my sawtooths (if any). I make a final call on what my average for deco purposes is then (it could end up being my max depth ala OW tables even)
This reminds me of a thread from maybe a decade ago. It started innocently enough, but it became a serious back and forth between several RD proponents and John Chatterton, who was advocating using two computers for yourself and two for your dive buddy, thus eliminating the "computer craps out" argument. One of the RD proponents said that doing all that depth averaging and calculations gave him something to think about during a dive. Chatterton was incredulous, saying something along the lines of "You need something to think about during a dive? I have plenty to think about during a dive, and it has to do with the dive I am doing, not math story problems."
 
This reminds me of a thread from maybe a decade ago. It started innocently enough, but it became a serious back and forth between several RD proponents and John Chatterton, who was advocating using two computers for yourself and two for your dive buddy, thus eliminating the "computer craps out" argument. One of the RD proponents said that doing all that depth averaging and calculations gave him something to think about during a dive. Chatterton was incredulous, saying something along the lines of "You need something to think about during a dive? I have plenty to think about during a dive, and it has to do with the dive I am doing, not math story problems."

Shrugs.

Reminds me of a well known FL cave instructor bragging at a shop about 8 or 9 years ago that his computer failed or flooded on a dive at Indian (cave). He had "no clue" how much deco he had to do - I didn't think that was something to brag about then and still don't. If someone needs 2, 3, 4+ computers to just have a basic idea of how much deco obligation they have, they aren't the kind of buddy I feel comfortable with awareness wise.
 
Actually a Shearwater computer can tell you exactly how profile changes will turn out (during a dive) if you know how to use it.

Can it tell you how long you can stay down for if you change from 60' to 80'? If you change from 60' to 80', and then stay there for 10 minutes, can it tell you how long you can stay down for if you come back up again to 60', before executing any portion of what I just mentioned?

You can adjust the GFHigh on Shearwater during the dive. Effectively adjusting for unexpected circumstances such as cold and workload.

You could also just watch the GF99 display and keep it below your new self imposed threshold.

This isn't the same thing as being able to determine the time elements I mention above.
 
UTD RD facilitates this smartness and forces you to think about your profile.

Well no, it's also a set of (questionable) rules that give an ascent. At best it then tells you to "oh just guess your deco you'll be fine", but it's not like it actually has value in adjustment that other algorithms wouldn't have in terms of how to shape your ascent.
 
Min deco and 32% and repetitive dives - seems to have a reliable track record for my purposes. At least here in cold water we don't do 3+ dives a day with square profiles and minimum surface intervals. Places were this is common (Bonaire) have profiles where you can easily and pragmatically add a ton of shallow "deco" time based on what you've been doing. So the tools provided for repetitive 32% diving with just a bottom timer just seem to work out in practice. The handwringing over residual N2 time has been ongoing since the early 2000s and it you are really doing 5 square profile dives a day on air the min deco rules are going to bite you in the butt. But with the widespread availability of EANx, the recognition of shallow stops, and the really that few divers race out of the water on repetitive multileveling dives anyway it just doesn't seem to be a problem in practice.

Exactly - in practical terms, it's not really a problem even though academically, it's fair game to say it's incorrect. But having simple, easy to remember rules has a value under this sort of "standardized deco"-paradigm, so the academic inaccuracy is disregarded because the practical significance is virtually nil. So long as one keeps that context in mind, there is no conflict.
It's when that "rule" or logic is taken out of context that it becomes conflictive - i.e. an understanding to the effect of "UTD says repetitive diving doesn't bring about any residual nitrogen - herecy!".
It has to be seen in a context, as described in the quote above.

I feel the same way of looking at things in a context is valid for the question on 32 vs. 25/25.
(on a sidenote, I elaborated a bit more on what context I see that in, in post #93)

I never said using a "science based" algorithm means you don't understand how it works. Simply following a computer does not allow you to predict future results on your profile. That is exactly the power that RD (GUE or UTD versions) gives you, and as you illustrated yourself how GUE RD does exactly that.

I agree with this. Without saying anything about computers, tables or any other solution, speaking purely about RD, it's extremely "holistic-predictive". I.e. I can glance over the deck and know exactly which I dives I can do, in detail, with it that day, in a matter of seconds. This has value and it extends into the water during the dives, too.

If someone needs 2, 3, 4+ computers to just have a basic idea of how much deco obligation they have, they aren't the kind of buddy I feel comfortable with awareness wise.

This is another benefit, definitely - developing awareness is pivotal, and I feel RD is one very effective means toward that end.

Well no, it's also a set of (questionable) rules that give an ascent. At best it then tells you to "oh just guess your deco you'll be fine", but it's not like it actually has value in adjustment that other algorithms wouldn't have in terms of how to shape your ascent.

That's your opinion, and you are of course entirely free to say that, but you've also said the following:

As for RD 2.0 being closer to buhlmann, I don't know

The prior of those two statements I disagree with.
I base my views on training in and experience with the use of various algorithms, computers, software, RD1.0 as well as RD2.0.
 
So make the actual comparison vetween RD 2.0 and buhlmann, showing they're similar ascents, instead of saying they are similar? Unless you expect us to take training just for the sake of getting 3 mathematical rules which are, so far, not likely to be the best available...
 
Well no, it's also a set of (questionable) rules that give an ascent. At best it then tells you to "oh just guess your deco you'll be fine", but it's not like it actually has value in adjustment that other algorithms wouldn't have in terms of how to shape your ascent.

An algorithm is by definition is a set of rules that provide you with an ascent profile as well. Again, compare a profile generated from Buhlmann GFs and one UTD RD 2.0 suggest; there is no practical difference. UTD RD 2.0 adds value because it uses bubble models to treat fast tissues and Buhlmann models to treat slow ones. No other algorithm or method does this that I'm aware of other than a Buhlmann model mimicking bubble models (by setting lower GF-low numbers) or a bubble model mimicking a Buhlmann one.

The value of RD has been beaten to death and reiterated time and time again in this thread and others on here. There will always be a community [ScubaBoard/internet divers] who will be vehemently against it, yet have either never used RD of any kind or have used it so little they have no basis to speak for it. They are always the first to speak out about it but the last to ever try it.

To summarize the benefit of UTD RD 2.0:
- Allows thoughtful development of awareness of ascent and decompression obligation
- Allows forward-looking practical estimations on how to change your profile, which no computer can do. Changing your computer's GFs mid-dive is not the same as determining how long you can stay down for at various depths for various times without having to perform those parts of the dive to see the results.
- Addresses fast-tissue off-gassing by applying deep stop theory to the ascent

I'm not opposed to using Buhlmann GFs; I dive with people all the time that use them. We adjust our profile to allow for short deeper stops and we've never had a problem with someone not clearing their computer. The practical difference just isn't there.

Finally, using Buhlmann GFs but adjusting an ascent manually based on other factors is in essence creating your own ascent strategy and not following an algorithm.

So make the actual comparison vetween RD 2.0 and buhlmann, showing they're similar ascents, instead of saying they are similar? Unless you expect us to take training just for the sake of getting 3 mathematical rules which are, so far, not likely to be the best available...

I did this last year in another tireless thread and even showed pretty graphs.
 
Here you go @mikeny9 and @Patoux01 :
image.png

So make the actual comparison vetween RD 2.0 and buhlmann, showing they're similar ascents, instead of saying they are similar? Unless you expect us to take training just for the sake of getting 3 mathematical rules which are, so far, not likely to be the best available...
I also made a plot that illustrates the profiles we've been discussing for a dive to 170' for 20 minutes using 18/45 and 50% O2 for deco:
View attachment 412330
 
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https://www.shearwater.com/products/perdix-ai/

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