UTD Ratio deco discussion

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Right, the ratio deco 2.0 is the result of the changes that came out of that study and puts the time from the middle of the curve on the shallower side. Take a look a thing the samples profile I posted.

As far as altitude diving, it's not built into ratio deco. My instructor told me to look at the standard ratio deco profile, then run it in a computer, compare the difference and make an informed decision.
 
All the UTD divers I know use computers on all non-training dives. Not a massive sample but still.

My understanding is as follows: In training, there is a (deliberately) high workload. Everything is geared toward emergencies and failures, including issues where a mental deco map may be required. Since using a computer is (or should be) a no-brainer by the time you get to tech training, the focus during training is on the other methodologies.

When I train (and examine) flying students, I don't allow them to use autopilot or many of the other automated systems after they are familiar with their use, purely since they will be using them on every routine flight after that. What I want to see is whether they can deal with the situation when those systems go all pear shaped.

From a training methodology side, I can see the principle of "train hard, fight easy".

Whether this is the original intent or not I couldn't say. I do know that UTD training philosophy is VERY much in line with aviation training methods, to the extent that the primary reference for instructional techniques is the FAA Flight Instructor's handbook.
 
As far as altitude diving, it's not built into ratio deco. My instructor told me to look at the standard ratio deco profile, then run it in a computer, compare the difference and make an informed decision.

I've taken their Tech 1 program and do deco dives on gauge mode. All the UTD trained divers I know doing tech profiles do the same (also a small sample too, about 8).
Can you put those two together and help me to understand how it works on an altitude dive?

You say they use computers in gauge mode (Or, I assume bottom timers) for their dives. That's what we did. We planned our dives ahead of time and had a written schedule using RD. If we had to stray from our plan, we would use RD to adjust on the fly.

So what happens at altitude? Do you compare the RD schedule and the computer program for altitude for your plan, make a personal judgment, and then write that plan down and follow it? If so, what do you do if your actual dive strays from the plan?

What software program is recommended? When I took my Ratio Deco class from Andrew (for which, BTW, he never gave me the card), every time we calculated a schedule using RD, an instructor in the room would make the same calculations using one of several desktop software programs, including V-Planner, DecoPlanner, and Gap. The schedules would always be different, and the message was that it showed why you should never use desktop software programs. Since ratio Deco gave the "proper" ascent profile, the differences between it and the commercial programs showed that the commercial programs were all wrong.
 
My experience with UTD (having spoken to the founders and instructors) is they promote "thinking divers" by telling them what to think. Their ratio deco concept is based on junk science and their rebreather program (if it still exists) was downright dangerous.
 
This could easily get off-topic into yet another discussion about ratio deco. However, I believe the main argument for ratio deco is that there's a big difference in trusting factual things, like depth, time, average depth, current temperature, etc. and trusting something which is computationally precise but questionably accurate like decompression. How you feel and other conditions of the dive may play a role in how much or how little deco you do using a UTD ratio deco approach (I make specific mention of the "UTD ratio deco," because the GUE ratio deco is terribly incomplete and only used in emergencies).

Also, you may think ratio deco is complex math, but to me it's really not. It's fairly simple arithmetic, not complex algebra or anything like that. I recently had a discussion with someone about a dive profile, which initially resulted in them running the profile in their program and it determined they needed to spend 55 minutes at 20' on 100% O2. They didn't realize until I told them that there's something terribly wrong with that plan, and it turned out to be a bug in the software (software was set to calculate last stop at 20'). Computers have their issues as well, as much as I hate to admit it (I'm a software developer by day).

Finally, if you compare ratio deco profiles to 30/85 Buhlmann profiles they are strikingly similar, so I wouldn't let ratio deco be the reason that one should avoid a UTD advanced class.

There is a difference between trusting facts like time and depth, and doing math in your head on the fly to come up with an ascent schedule, compared to trusting a device that is computationally precise, and does its computations using the same facts? Yeah. One has all the hard math done by a human. The other has all the hard math done by a computer and the human only has to apply their judgment to modify the results if and as conditions warrant.

I am also a software developer by day. If you think that it is a bug when a piece of software calculates an ascent schedule that is too long because it is set for a last stop of 20', all I can say is that I am glad we don't work together.

Producing results that are "close to" a Buhlmann ascent using GF30/85 is one very good reason I would avoid that, *ahem*, "strategy. I use GF50/80. GF Lo of 35 is too low (in my opinion), producing a first stop that is too deep. And GF Hi of 85 is not as conservative as I choose to be on deco dives. Further, having asked a couple of respected people in the field, it seems to me that a GF Lo that is even higher than 50 might even be better. So, GF Lo of 35 is just really too low.

Ah yes, that study. I think everyone is pretty much in agreement these days that strict VPM isn't so safe. From what I understand, the ratio deco approach maintains some deep stop theory to avoid too large of bubble sizes, much less than a strict VPM. For example, if you shape your O2 window from 70' to 30' and determine you need 1 min stops, but the deep stop table has you maintain 3 min stops, then you'd have to keep 3 min there to avoid too much bubble growth. That's where the "ascent strategy" comes from: they use deep stop theory to get to the O2 window and shallow/slow tissue zones. The approach aims to keep on-gassing of the slows to a minimum but also tries to control the bubble size to some extent.

The deep stops used to start at 75%, but now they are 66%. There is a 75% stop if you exceed NDL by 30 min, but haven't exceeded it by more than 45 min. However, those profiles are impractical for a Tech 1 student because you'd end up with too much deco time and would need a 50% and 100% O2 bottle. Also, when shaping the O2 window, ratio deco 2.0 prefers to add the "stolen" time from the middle to the shallowest (30') stop. So for example, a BT of 30 min at 150' using 50%, your ascent would look like:
Ascend to 100' at 30 FPM
100': 1 min (deep stop theory)
90': 1 min (deep stop theory)
80': 1 min (deep stop theory)
70': <switch 50 %> 3 min (O2 window)
60': 3 min (O2 window)
50': 2 min (O2 window)
40': 2 min (O2 window)
30': 5 min (dissolved gas theory)
20': 12 min (dissolved gas theory)
10': 3 min (dissolved gas theory) (or 20' 10 min 10' 5 min, etc)

I've compared a lot of profiles to my GUE friends and it's very similar to what they come up with in DecoPlanner that I wouldn't have a problem using their profile and everyone I'ved talked to (about 4 people so far) wouldn't have a problem doing the UTD profile either.

Well, at least there was no complex math to do in your head to get to that answer...

I got an email warning me that if I ever wrote anything like that again in a public forum, my name would be turned over to PADI for violating the member standard against making derogatory statements about other agencies. I would thus face disciplinary action from PADI, possibly expulsion, for making such a statement.

Did you really mean to say PADI there? It seems like you might have meant UTD.
 
My experience with UTD (having spoken to the founders and instructors) is they promote "thinking divers" by telling them what to think. Their ratio deco concept is based on junk science and their rebreather program (if it still exists) was downright dangerous.

Yes, dangerous with ZERO incidents as compared to other safer alternatives.
 
Thank you for your candid response. Just a quick question: when you said using Ratio Deco, does that include using the standard gases that goes with Ratio Deco or was other gases used? I did a couple of tech dives at altitude with my group and we were high from the whiskey after the dives.
We almost always used standard gases--at least we tried to. Mixing trimix out of the back of a van with no booster on the open prairie can lead to some compromises.
 
How many UTD rebreather divers are there? Active? I know a few who have returned to OC.

Doesn't matter. Zero is Zero. Anyway you spin it, its still Zero.
 
https://www.shearwater.com/products/perdix-ai/

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