Slow tissue on gas from stops

[PfcAJ]

AJ is talking about using a depth time relationship to guesstimate how changes to the dive profile will affect the overall deco obligation. He's definately not talking about using RD as taught by UTD.

I'm a bit surprised that diving a CCR you seem unaware that with deco there is a relationship between time and depth. This is part of the simple basics for deco algorithms.

Unfortunately for everyone, UTD has taken a handy tool (ratio deco) and totally ditched the idea of using a real algorithm as a baseline. That’s where things went sideways. The “ratio” became the standard instead.

 

[Jack Hammer]

Unfortunately for everyone, UTD has taken a handy tool (ratio deco) and totally ditched the idea of using a real algorithm as a baseline. That’s where things went sideways. The “ratio” became the standard instead.

I try to call it a depth time relation instead of ratio deco to more clearly separate it from what they do.

 

[PfcAJ]

I try to call it a depth time relation instead of ratio deco to more clearly separate it from what they do.

That offends my delicate sensibilities.

 

[leadduck]

A certain algorithm (gradient factors of your choosing, this is hypothetical) gives you 30mins of time on 50% after spending 30mins at depth. You adjust your bottom time and see that 25mins at depth results in 25mins of deco, and 35mins results in 35mins of deco. That “ratio” is 1:1. You verify it across a range of times and see the limits of that ratio. That’s it.

(...)

It’s not some crazy thing PROVIDED you’re using an algorithm as your baseline (like buhlmann 40/85, for instance).

I think one problem with using one algorithm as a baseline is, that the relation between deco time and bottom time is nonlinear; the limits of that ratio are not well defined.

Let's start with a dive that fits your example, to 42m for 30min bottom time with Tx21/35 and Buehlmann 60/80, which gives me 30min deco time on 50%; like in your example, a ratio of 1:1. I adjust my bottom time to 25min and get 23min of deco; I adjust my bottom time to 35min and get 37min of deco.

Can I ignore that deviation of 2min extra deco time? Let's say I stick with 1:1 and do only 35min deco for 35min bottom time, that's like increasing GFhigh to 85. For 45min bottom time (+15min), doing only 45min deco as suggested by my ratio (instead of the 51min of the exact algorithm) is like increasing GFhigh to 90.

The RD practitioners I know (some of my GUE trained buddies) in my experience do not think about it in such detail. They apply it like a rule as they learned it, did not adjust it to some algorithm, do not think about how the gradient factor grows significantly even for +5min bottom time and how narrow the range is.

 

[elmo]

I think one problem with using one algorithm as a baseline is, that the relation between deco time and bottom time is nonlinear; the limits of that ratio are not well defined.

Let's start with a dive that fits your example, to 42m for 30min bottom time with Tx21/35 and Buehlmann 60/80, which gives me 30min deco time on 50%; like in your example, a ratio of 1:1. I adjust my bottom time to 25min and get 23min of deco; I adjust my bottom time to 35min and get 37min of deco.

Can I ignore that deviation of 2min extra deco time? Let's say I stick with 1:1 and do only 35min deco for 35min bottom time, that's like increasing GFhigh to 85. For 45min bottom time (+15min), doing only 45min deco as suggested by my ratio (instead of the 51min of the exact algorithm) is like increasing GFhigh to 90.

The RD practitioners I know (some of my GUE trained buddies) in my experience do not think about it in such detail. They apply it like a rule as they learned it, did not adjust it to some algorithm, do not think about how the gradient factor grows significantly even for +5min bottom time and how narrow the range is.

So in your example it looks an awful like the ratio by which you would adjust your deco time relative to bottom time is 1.4min/min (or 1:28/min). This ratio holds for the entire range of bottom times (25-45min) you specified. Just because the ratio isn't a round number doesn't mean it doesn't exist or isn't helpful. Of course your ratio differs from the ratios taught/observed in GUE classes (I have no experience with other DIR organizations so won't comment on them), because you've adopted different gradient factors, and perhaps a different definition of where "deco time" starts (i.e. does it include the time to ascend to the first stop).
In your case, I'd write down and remember the plan you'd worked out, as well as the 7min difference in deco time per 5min differrence in bottom time. I'd do something similar with variation in depth too.
As an aside, the Subsurface planner can calculate the bottom time and depth variations for you as +/-min/min and +/-min/m.

 

[Dan_P]

I've summarized a snack list of misunderstandings from throughout this and other discussions online and off.

For my part, I'm surprised to see how often divers who seem to have a strong opinion against an aspect of other people's/organization's diving, land on a misconception because they either don't understand the topic altogether or aren't aware of key elements.

This seeks to address some such elements in relation to this discussion and Ratio Deco.

1) "UTD forces people to use Ratio Deco"

Absolutely not. UTDs standards have (I believe) always been, and remain, open to let instructors or divers make the choice for themselves. UTD offers Ratio Deco, but instructors/divers can choose whichever option they prefer.
With most organizations, I believe, it's only "instructors/divers choose", and that's pure CYA.

2) "Ratio Deco is a written in stone"

We have seen from UTDs procedures that it is not written in stone, but in fact is very open to personal adaptation.

3) "Ratio Deco is an algorithm"

We have seen examples of differences across an algorithm and a distribution pattern-style framework. UTD describes RD as "not a scientific formula", but rather an ascend strategy that the user can adapt. Some of the organization's goal with it appear to be making divers engage in their decompression, developing their working knowledge, and creating thinking divers. It cannot then be said to work in the same way that an algorithm does.

4) "Ratio Deco is dangerous"

We have seen how science-based knowledge available at this time, does not support a view that RD is dangerous, unsafe or irresponsible.
Suboptimal? Sure, "standard" is suboptimal compared to "optimal" in either case. It is not controversial.

5) "UTD is a personal cult"

I'm increasingly gaining sympathy for a notion that anti-UTD is a personal cult gravitating towards AG and disregarding facts, including occationally some of the above.

 

[rsingler]

...the Subsurface planner can calculate the bottom time and depth variations for you as +/-min/min and +/-min/m.

Where is this function, please?

 

[leadduck]

So in your example it looks an awful like the ratio by which you would adjust your deco time relative to bottom time is 1.4min/min (or 1:28/min). This ratio holds for the entire range of bottom times (25-45min) you specified. Just because the ratio isn't a round number doesn't mean it doesn't exist or isn't helpful.

You're making a difference between the ratio (30min deco time / 30min bottom time = 1:1) and the sensitivity (+7min deco time / +5 min bottom time = 1.4:1). That's good, but that's not how ratio deco is taught. Ratio deco is meant to be calculated by the diver on the fly; it's usually taught with fixed integer ratios 1:1, 2:1, or 3:1, for certain depths. To interpolate between these depths, the diver adds or subtracts numbers, but doesn't use non-integer ratios.

 

[PfcAJ]

I think one problem with using one algorithm as a baseline is, that the relation between deco time and bottom time is nonlinear; the limits of that ratio are not well defined.

Let's start with a dive that fits your example, to 42m for 30min bottom time with Tx21/35 and Buehlmann 60/80, which gives me 30min deco time on 50%; like in your example, a ratio of 1:1. I adjust my bottom time to 25min and get 23min of deco; I adjust my bottom time to 35min and get 37min of deco.

Can I ignore that deviation of 2min extra deco time? Let's say I stick with 1:1 and do only 35min deco for 35min bottom time, that's like increasing GFhigh to 85. For 45min bottom time (+15min), doing only 45min deco as suggested by my ratio (instead of the 51min of the exact algorithm) is like increasing GFhigh to 90.

The RD practitioners I know (some of my GUE trained buddies) in my experience do not think about it in such detail. They apply it like a rule as they learned it, did not adjust it to some algorithm, do not think about how the gradient factor grows significantly even for +5min bottom time and how narrow the range is.

If it’s close enough is up to the diver to decide.

For me, on short ocean bottom times, it’s definitly close enough.

 

[UWSojourner]

This seeks to address some such elements in relation to this discussion and Ratio Deco.

1) "UTD forces people to use Ratio Deco"
Absolutely not.

I'll take your word on that.

2) "Ratio Deco is a written in stone"
... in fact is very open to personal adaptation.

I'll take your word on that too.

3) "Ratio Deco is an algorithm"
UTD describes RD as "not a scientific formula", but rather an ascend strategy that the user can adapt.

A bit definitional. I get that you want to position your business a certain way. On the other hand, once it's a set of rules that leads to a schedule, it's an algorithm. But hey, not a big deal. If UTDers picture themselves as decompression generals strategically moving the stop minutes, I'll play along.

4) "Ratio Deco is dangerous"
We have seen how science-based knowledge available at this time, does not support a view that RD is dangerous, unsafe or irresponsible.

This misrepresents the scientific picture. All the scientific information we have says that deep stops add risk to profiles. One study specifically studied UTD-RD and, although it was granted 44% more stop time, the profile generated higher decompression stresses than a GF30/85 profile without the additional time. As such, we can conclude that the UTD-RD profile tested was at least 44% inefficient by the study's test criteria.

Current research would support the idea that UTD-RD is more dangerous, and less safe than readily available alternatives that don't emphasize deep stops. In my view it IS irresponsible to downplay this research and the potential that it could be indicating levels of risk unknown to us due to lack of study that a diver might not want to assume if known.

5) "UTD is a personal cult"

I've seen some of the online UTD videos. This cult seems very impersonal to me.