My Journey into UTD Ratio Deco

[rjack321]

It does not put it at rest for me.

From whom do you seek this training? From someone from another agency?

Does UTD not teach anything about altitude diving?

Do UTD divers never dive at altitude on their own?

Why has this changed from the time I was in UTD and we were told very specifically and very emphatically that altitude does not matter and nothing different needs to be done when diving at altitude?

But the course has (conclusively/obviously) changed. Maybe they said that back then, mistakes have been made by all agencies over time. Curricula change and adapt over time. GUE doesn't offer an altitude course either, and my TDI and NSS-CDS courses have not addressed altitude either. UTD is not obligated to provide altitude training unless they are still teaching and doing official class dives at altitude (maybe they are, I dunno)

 

[rjack321]

Yeah, what victorzamora said. I think you may be confusing 100% or GF100 with the point where you start off-gassing; GF100 is experienced where a tissue is so supersaturated compared to the instantaneous ambient pressure that it has hit 100% of the maximum 'allowed' in the Buhlmann model at that point in time, or 100% of the M-value. Buhlmann says you cannot safely off-gas faster than this..)

I think you're right on this, even if I have never really liked those graphs, appreciate your correction.

Still think 100/70 is crazy to try and apply in the real world - but that opinion has about as much science behind it as RD's approach to allocating deco time across the ascent (none).

 

[victorzamora]

I think you're right on this, even if I have never really liked those graphs, appreciate your correction.

Still think 100/70 is crazy to try and apply in the real world - but that opinion has about as much science behind it as RD's approach to allocating deco time across the ascent (none).

Picking those GFs has no scientific backing, that's correct. However, Buhlmann ZHL16-C w/ GFs applied is a much more scientifically-backed approach than UTD's RD. So, picking specific GFs is a bit of witchcraft....but at least there's serious backing of the underlying principles.

 

[rjack321]

Picking those GFs has no scientific backing, that's correct. However, Buhlmann ZHL16-C w/ GFs applied is a much more scientifically-backed approach than UTD's RD. So, picking specific GFs is a bit of witchcraft....but at least there's serious backing of the underlying principles.

The original RD used 30/85 as a baseline to derive the total deco times. i.e. 150ft for 20min = 20mins on 50%. +5mins = +5mins 50%, +10ft = +5mins. Hence it is no surprise to me to see RD and 30/85 looking pretty comparable (in the Spisi thread) with RD having slightly higher gas loads as a consequence of the time shift deeper.

Back then (early 2000s) 30/85 GFs and Yount's bubble work were all the rage. Moving some of the 30/85 time deeper made "logical" sense absent any evidence that bubble models were actually riskier. Its sad to see people still holding onto the "protect the fast tissues with deep stops" paradigm. GFlow of 100 is perhaps swinging the pendulum a bit too far the other way, but its hard to know since again we have no real evidence for that aggressive of an initial ascent.

 

[mikeny9]

Why has this changed from the time I was in UTD and we were told very specifically and very emphatically that altitude does not matter and nothing different needs to be done when diving at altitude?

He said... she said...

 

[Dan_P]

What @mikeny9 said.

On another note, if one learns about RD formally, or just reads "the book", one will be informed of what it's based on.
One can say that one doesn't agree with the basis of it, and that's perfectly fine, but it's not witchcraft

That said, in fairness, it doesn't look like it's optimal either "out of the box", so I understand that some are dismissive of it - I guess the only thing I can say to that is a reiteration that it's really not an algorithm.

And, perhaps that, if I were using a PDC, I wouldn't add the "out of the box"-RD framework into it as an algorithm.
There are others which are in all probability closer to optimal by some degree.

To me, it's less about what the correct deep stop emphasis is, and more about whether I want to use a PDC or a "standardized deco framework".
I choose "Standardized Deco Framework", and can adjust towards what I believe to be the correct deep stop emphasis within it, just like another diver can choose PDC and adjust towards what they believe to be the correct deep stop emphasis within that. I don't have a problem with that.

 

[rjack321]

He said... she said...

Well I heard what @boulderjohn heard about altitude too at one time. And friends of mine were diving in Lake Tahoe with minimal altitude adjustments, so for a time I believed it as well. So it was (incorrectly) taught that way IMO. Times change, I am glad they dropped postulating about how altitude is not relevant even if it took awhile to get there. Provides some hope that the current shift RD has towards more time at depth will eventually shift as well.

 

[dmaziuk]

Still think 100/70 is crazy to try and apply in the real world ...

Rumour has it typical "NDL" implementations do not check GF low, which effectively makes it 100 on every no-stop dive. Whether a tissue compartment can theoretically get anywhere near "100% of M-value" on the "low" end on a no-stop dive is another question.

 

[rjack321]

Rumour has it typical "NDL" implementations do not check GF low, which effectively makes it 100 on every no-stop dive. Whether a tissue compartment can theoretically get anywhere near "100% of M-value" on the "low" end on a no-stop dive is another question.

Yes which is perhaps why some squarer rec profiles end up being pretty provocative DCS wise.

 

[boulderjohn]

He said... she said...

I assume by this that you are publicly accusing me of lying.

Here is a thread I started in March of 2011 in which I talked about it.

Differences in Ratio Deco

In that thread I mention a conversation I had via PM with Jarrod Jablonski of GUE on that topic. Jarrod said that a GUE diver should not use RD at altitude because it was not devised for altitude diving. I have preserved that conversation but will not print it unless Jarrod were to agree to that.

I was still a UTD member than, although that ended pretty quickly after that. I was threatened by UTD because of the thread. I was told that if I started a thread like that again, I would be reported to PADI for violating their standard against disparaging another agency, and I could be expelled. That pretty much finished off our relationship.