mikeny9
Contributor
Thanks Kev 
My Journey into UTD Ratio Deco
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I don't really know how you do this. On this profile at runtime minute 30 I would be up somewhere around 40ft. You would be down around 70ft on RD - 1 ATA below me.
So if you shorten up the deep stops for buhlmann diving buddies and you are up around where buhlmann is, why not do it all the time?
I fell off the RD bandwagon about 5 yrs ago. But on CCR, diving 40/80 matching up with an RD OC diver is pretty much a joke. 20mins at 170ft with 15/55 dil and a setpoint of 1.3 I don't often even have a stop until around 60ft. And that stop might even clear before I get there. So I am twiddling my thumbs through all your 100-40ft time. My deco doesn't even really start until you are halfway through. That's because 1) you have an inert gas switch and I don't and 2) your consistently too darn deep to really be anything like Buhlmann.
mikeny9
Contributor
I don't shorten deep stop times. For a 170' dive, the additional stop time is 3 minutes between 110' and 90'. Three minutes in that range isn't anything to fight about practically; anyone who thinks one is going to have a significant slow tissue problem in the shallows by spending an additional 3 minutes between 110' and 90' is likely an expert internet diver. My buddies' computers always clear on these profiles so they don't mind. Besides, 170' is probably the most extreme example. A more typical profile for us is a 110' dive using O2 for deco. The deep stops are at 70' and 60' for 1 min each; again 2 minutes is nothing to shake a stick at.
In the scenario you mentioned, your computer isn't telling you to stop at 60' because it's using a Buhlmann-based algorithm; of course it's going to want to push you shallower than any UTD RD 2.0 profile. The UTD 2.0 ascent strategies are designed to address bubble growth in your fast tissues, which a Buhlmann model won't do.
I'd rather address potential bubble growth in my fast tissues than get shallower quicker just so I can get out of the water quicker.
In the scenario you mentioned, your computer isn't telling you to stop at 60' because it's using a Buhlmann-based algorithm; of course it's going to want to push you shallower than any UTD RD 2.0 profile. The UTD 2.0 ascent strategies are designed to address bubble growth in your fast tissues, which a Buhlmann model won't do.
I'd rather address potential bubble growth in my fast tissues than get shallower quicker just so I can get out of the water quicker.
That's not what I asked.
If you aren't shortening the deep stop + the first ~5mins on 50% times then your buddies aren't following a buhlmann profile - they are doing your profile. You cant do both RD (as UTD teaches it) and a buhlmann ascent at the same time. Admittedly for a 20minute dive its pretty much a wash. I don't really care about a grand total of ~2-6 extra minutes which are "too deep". However, once you step past the squareish wreck type dive with the ~15-30min BTs RD diverges more and more from an efficient ascent. The setpoints no longer work for 60-120+min BTs and instead of a mere ~5mins which is "too deep" (in the example graph) you end up with a way too much time at intermediate (90-40ft) stops and far to short of times in the 10-30ft. I.e. making these big 2+ hours of deco curves with arithmetic no longer works - they are algebraic power functions (square and or cube functions not multiple add/subtract)
I recommend reading the NEDU threads again (if you can put up with them), and focus on the HEAT graphs. Yes you are keeping the fast tissues further below their overpressure points. In the process you are actually continuing to load intermediate rate tissues. Post-dive intermediate tissues end up with high gas burdens to offgas at the surface and increase your probability of DCS. The spisi study demonstrated that there is measurably greater decompression stress despite the fact you are doing more deco time with RD.
mikeny9
Contributor
What depths/BTs are you referring to? UTD RD 2.0 has "cascading ratio deco" for certain depths and times which might match more of the schedule you're looking for. You definitely can't perform a Buhlmann-based ascent on a UTD RD 2.0 profile, as UTD RD 2.0 is not Buhlmann; it incorporates it but it isn't the same. My buddies who set their computers to Buhlmann GFs usually end up clearing their computers anyway when we are on the shallower stops but we are doing UTD RD 2.0 profiles. Forgive me but I'm still not sure what you're asking.
This is why more time is spent in the shallows with UTD 2.0 than a standard Buhlmann-based profile. Also, it's important to understand what type of decompression stress we might be exposing ourselves to. I'd rather be more exposed to Type I DCS than Type II.
PfcAJ
Contributor
mikeny9
Contributor
You’re entitled to your opinion AJ. It’s more of a slowing of the ascent. Thirty second pause and 30 second roll up.
Perhaps a look at the actual supersaturation pressure patterns might help, and stop some of the "blame it all on deep stops" nonsense arguments from developing.
Here we see that the RD profile is a bit of a mess for supersaturation: The initial ascent is 20% improved over the 30/85. The supersaturation comes to a stop in the mid ascent phase, so RDS really does protect the middle ascent from injury. The last stops and surfacing pressures are about the same for both.
Note also (not shown) is that both profiles finished and surfaced with less than the ZHL-C max value (for this dive) of 0.65 ATA.
So let me make some point relevant to the last few posts.
The "slow tissue on gas problem", did not actually cause a problem, and is insignificant to the result (just like all deep stops in real use).
The surfacing off gas is near identical in both, and a 5 minute change to bottom time would be far more significant than the small differences seen above.
Enjoy.
Here we see that the RD profile is a bit of a mess for supersaturation: The initial ascent is 20% improved over the 30/85. The supersaturation comes to a stop in the mid ascent phase, so RDS really does protect the middle ascent from injury. The last stops and surfacing pressures are about the same for both.
Note also (not shown) is that both profiles finished and surfaced with less than the ZHL-C max value (for this dive) of 0.65 ATA.
So let me make some point relevant to the last few posts.
The "slow tissue on gas problem", did not actually cause a problem, and is insignificant to the result (just like all deep stops in real use).
The surfacing off gas is near identical in both, and a 5 minute change to bottom time would be far more significant than the small differences seen above.
Enjoy.
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