Differences Between UTD and GUE
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Blackwood
Contributor
Sorry for the sarcastic comment, BTW.
The Ratio Deco setpoints were meant to envelope the total decompression obligation for specific gas combinations (e.g. 21/35 + 50%) as determined by DecoPlanner (Buhlmann and VPM).
Discussions here about 'feel' have to do with how we shape our curves, not which how much deco we need to do or how we determine that quantity.
Example:
110ft, 40mins, 25/25 + O2
1:1 version
110ft is 40ft shallow than 150 = minus 20mins
40-20 = 20mins deco (requires using O2 in the proper range)
split time above and below 20ft
profile looks like this
10-5
20-5 (any combo of 20&10ft stops adding up to 10mins is close enough)
30-3
40-3
50-2
60-2
70-1 (add deep stops)
80-30sec slide
fibonacci-like version
110ft MDL with -10% EAD for 25/25 = 20mins
40min is 20mins over plus 6min MDL ascent = 26mins backgas deco
rough backgas shape (cheater version of a fibonacci sequence takes 1/2 of total and puts it at 10ft, 1/2 of remainder at 20ft, 1/2 of remainder at 30ft and so forth until you add up to total time), so:
10-13
20-6
30-3
40-3
50-1
60-1 (add deep stops)
70-1
80-30sec slide
account for 50% time credit on O2 and reshape the shallow stops to address O2 window, 19mins at 10+20ft = 9.5mins total O2 time, rounded up to 10mins (same as 1:1 method).
revised profile
10-5
20-5
30-3
40-3
50-1
60-1
70-1
80-30sec slide
Pretty similar profiles, the fibonacci-like sequence method using backgas with O2 time credit gives you slightly less time in the deeper portions of the deco. Although once you fill down the deep stops to 70-75% of depth its pretty much a wash.
Disclaimer: don't learn to deco dive on the internets
You need to be careful in when you say "50mins of deco" for a 180ft RD dive as that is typically only the time on the deco gases (EAN50 and O2) and does not account for deep stops. As you get into bigger and bigger dives the RD lingo suggests more and more aggressive deco because the deep stops are integral and assumed, but when we talk about the "total time" here on the internets we rarely include that backgas time.
E.g.
decoplanner might say 50mins of deco which is starting at 50ft
while
RD says "40mins of deco" but there's 9-11mins of deep stops on backgas that most of us don't add into that total.
Its a terminology thing.
BTW, as far as I can tell, GUE does not have clear guidance on how to apply RD to shallower O2 only deco dives. They didn't when I took GUE Tech1 and they still don't seem to. In fact its gotten a bit more confusing since the MOD for 30/30 moved up to 100ft.
A 110-120ft dive for GUE would use 21/35 and EAN50 for deco. Personally, I have done 21/35 dives in the 115ft range with EAN50 & 15-20mins of deco and I felt awful. I prefer O2 deco for these slightly lengthened MDL-ish dives.
A 110-120ft dive for GUE would use 21/35 and EAN50 for deco. Personally, I have done 21/35 dives in the 115ft range with EAN50 & 15-20mins of deco and I felt awful. I prefer O2 deco for these slightly lengthened MDL-ish dives.
Blackwood
Contributor
Try 55 minutes at 100 feet on 32%.
The additional 5 minutes of MDL added to the time-over method is eaten up by the reduced credit (100 is 25 minutes away from 150, whereas MDL is 30 minutes).
So,
100 for 55 @ 1:1 = 55-25 = 30 minutes deco
Something like 70/1, 60/1, 50/2, 40/4, 30/6, O2: 20/8, 10/8
100 for 55 @ time-over = 55-30 = 25 minutes deco + 5 minutes min deco = 30 minutes
Something like 70/1, 60/1, 50/2, 40/4, 30/6, 20/8, 10/8 all on backgas
Per the ratio document, going to oxygen could halve the 20-0 segment, bringing the total deco down to ~ 23-25 minutes (depending on how you split and shape it). It's not a lot of time (magnitude), but as a percentage it's fairly significant.
I emphasized the word "could" because that was the response I got when I posed this question to Jeff and Andrew. "You can adjust, but you don't have to." But it still seems weird to me that you're 'penalizing' helium in a system which promotes it as not contributing much to deco due to insolubility.
Agreed. The entire system is meant to envelope DP obligations. Ignoring the deep stops isn't ratio deco.
1:1 is only for:
25/25 & O2
or
21/35 & EAN50
Not for 32%, 1:1 does not account for -20% EAD.
Thus this:
is a massive overestimate of required O2 deco. Since 32% is used to a max of 100ft and 1:1's upper end is 100ft there's really little or no overlap in ranges.
Down to 100ft, 32% & time over MDL is really the only method.
1:1, 150ft setpoint
100-130ft, 25/25 & O2, or for
120-170ft, 21/35 & EAN50
by a quirk of the math the -10% EAD of 25/25 and the modest MDLs in the 100-130ft range are quite similar to the a 1:1 which is otherwise using -0% EAD 21/35 and a null time MDL. This doesn't happen with other gases, depths, choices.
1:2, 200ft setpoint
170-210ft 18/45, EAN50 & O2
1:3, 250ft setpoint
220-260ft 15/55, EAN50 & O2, possible 35/25
Below 250ft, Cascade deco.
Bottom line, they all have required gases and don't work outside their ranegs/gases. You can find new curves if you'd like, there are for sure relationships between depth/time/deco/gas reagrdless of gases or setpoints used. These are just the RD "standards"
Blackwood
Contributor
Can you point to that somewhere? It wasn't what I was taught, nor was it brought up to address my question.
It makes sense*, but I'm surprised that this is the first I've seen it.
*though it still seems weird to me that +25% He - 7% O2 is penalized within the UTD concept of gas dynamics.
Rainer
Contributor
That's because you're not "doing it right". Per GUE R3, you should be decoing on 32% for these dives. Your buoyancy standards are also probably too high. Try bouncing around more. It helps too if you're worried the whole time about what to do in case you have a "dynamic" valve failure. The stress will increase off-gassing.
LOL.
Rainer
Contributor
The above is pretty much what I do as well. 100' and less is 32% and time over MDL (credit O2 if you bring it). For 100-120' I prefer 25/25 and O2, but have done and will do 21/35 and 50%. For both, I do time over MDL (not 1:1). For me, 25/25 is a 10% credit (not the 20% UTD seems to be teaching now). 21/35 dives like air. For 130-170' I'll usually bring 18/45 (more flexible gas if getting blown out). It basically dives the same as 21/35.
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