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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.
Can you put those two together and help me to understand how it works on an altitude dive?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).
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.
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.
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.
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.
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.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.
How many UTD rebreather divers are there? Active? I know a few who have returned to OC.