Ongoing discussion of Ratio Deco

[limeyx]

Noone has really answered the criticism that DOTF is inconsistent in its "conservatism-settings" thru-out the same range ie T1 or T2 (or maybe I missed it). Do you agree but don´t care (perhaps because you modify the "output" in the less conservative parts of the range) or disagree?

I dont see anything that needs answering honestly

1) Plenty of people do T1/T2 dives using all kinds of deco planning s/w or even dive computers and most get out of the water without incident
2) The claim was that ratio deco was "inconsistent" with DecoPlanner, BUT you have to understand that
- the people using DecoPlanner are actually doing something essentially almost just like ratio deco but using DecoPlanner for part of the task (but not all)
- Ratio Deco makes use of deep stops, O2 window, treating Helium in theory in a more modern/understood way then DecoPlanner, so yes you can say it is "different" but in this case that does not necessarily mean "wrong" It is just that -- different, and that's one reason *why* it is used -- because certain people believe it gives better deco results than straight decoplanner

 

[ScubaMilo]

Agreed.

I am however, somewhat surprised at your take on RD, given who I think your instructor for tech was ???

Your right again,
But just because I'm taught something by someone even though I think they are a great diver and Instructor I don't have to blindly follow their path.
I have through trial and error found ratio deco to have a place in my diving, but I do not rely on it for my sole means of deco planning.

This is the only point I have been trying to make.

Milo

 

[cool_hardware52]

The two are kind of different concepts.

"Deep Stops" attempts to reduce bubble growth by slowing the ascent at a deeper depth than traditional deco algorithms suggest. In theory since the bubbles are really small at these depths, they are easier to crush/eliminate than when they get big (as they would on a straight DecoPlanner profile).

The theory is, that the reasoning against deep stops that goes like "let the bubbles grow a bit bigger and do more time shallower" doesn't really work well because by that point the bubbles are much much harder to get rid of, and this leads to fatigue.

Also, the theory (I think) is that allowing those bubbles to grow, could lead to a higher chance of a typeII hit.

Min deco is simply the least amount of deco you can do for a given dive profile and exit the water safely (more deco is always allowed

Min deco is a bit confusing because we usually use it to refer to MDL/NDL type diving, but really we do calculate a "minimum deco" for every dive we do, which we can then pad if we see the reason (cold water, stiff current etc.)

I am aware of the concerns about bubble size and the benefits of keeping the bubbles small, but the first tissues to load on the dive and the first to unload during any ascent are the same, i.e. the fast tissues. Deepstops treat fast tissues. Doing the stops deep improves the efficiency via the reduced bubble size, but it's still the fast (Type II) tissues that are of interest. Treating the tissues likely to cripple vs the tissues that generate the Type I problems is part of the overall philosophy. If circumstances force a reduction in the shallow deco times (cold, current, etc.) you have improved the chances of surviving without permanent injury.

If your dive is short / shallow (MDL or NDL) do you have any significant load in the "slow" tissues?

Min deco is treating the fast tissues, as there is no meaningful load in the slower compartments.

Consequently min deco = "DeepStops" even if the stops themselves are in shallow water.

Any dive will require "deepstops". As the dive gets deeper you need to use more of the segments of the curve. As the dive gets longer the horizontal axis gets longer, meaning the time in each segment will increase. I've found that a handy way to picture where I might be on the curve and why.

Deepstops are so named because of their origin, but I find it easier to think of them as "fast tissue" stops.

Tobin

 

[limeyx]

...
Deepstops are so named because of their origin, but I find it easier to think of them as "fast tissue" stops.

Tobin

I agree 100%. In fact if you look at the "min deco" and then look at "collapsing" a ratio deco profile to 40,50,60 etc. feet up to 100, you see that you do essentially get the same thing

i.e. that min deco for a 100 foot No deco dive, is essentially the "deep stops" you would get for a deco dive for say 30-60 mins at 100 feet.

This was one of those "ah-ha" moments for me in tech1 -- where I got to see the relationship between deep stops/min deco on a tech dive, and the MDL/min deco rules we learned in DIR-F

From what I understand, there are similar "ah-ha" moments in Tech 2 also, but thats a long ways off for me.

 

[rjack321]

Law of primacy in effect...I guess they just don't care.

Chris

Actually I do care, but missed the earlier post.

The fact is that nobody (at least who I know) dives 100/100 decoplanner (straight buhlmann) or even 30/85 profiles. They are always "tweaking" things. Why is that?

Because decoplanner (nor any other currently available program IMO) isn't the whole story. Another way to think is that "its wrong". Human bodies don't work like a bag of M-values. Richard Pyle and others figured this out decades ago.

If you accept that decoplanner is not the voice of god for deco, i.e. its fundementally wrong before you even get to your gas switch, there's no sense in arguing that other aspects of its profile are somehow "correct".

In other words...
I don't accept decoplanner as a benchmark against which to rate other types of profiles.

From what I gather, some of you accept decoplanner total deco times as a benchmark against which to compare other methods. Fine, no problem, go for it. VPM is at least getting better than Buhlmann. But I still don't think its a coherent planning approach by itself. (I will actually use GF decoplanner for "what if" scenarios, that's about it.)


So, what do I accept as a benchmark?

The collective experience of myself and more experienced divers. Ratio deco is a framework which encapsulates this collective experience for me. Fundementally: deep stop bubble control, O2 window offgassing, and gradient/dissolved offgassing. I now have enough deco experience to start to tweak my ratio deco approach based on my own experiences. In other words, to start going beyond just using other's experience and incorporate my own.

These newish personal rules for typical 140-160ft T1 dives are:
add time (~3 mins) shallow on 21/35, ratio doesn't give me enough.
use 18/45, its way better than 21/35 for post-dive energy levels.

I hope this clarifies my approach and esp. why the entire concept of defining a "validated scientific" approach is missing the point. Real deco divers are where the rubber meets the road, we are the ones doing the validating. If nobody can or wants to actually dive a decoplanner profile, I think that says alot about its validity.

 

[limeyx]

Actually I do care, but missed the earlier post.

The fact is that nobody (at least who I know) dives 100/100 decoplanner (straight buhlmann) or even 30/85 profiles. They are always "tweaking" things. Why is that?

Because decoplanner (nor any other currently available program IMO) isn't the whole story. Another way to think is that "its wrong". Human bodies don't work like a bag of M-values. Richard Pyle and others figured this out decades ago.

If you accept that decoplanner is not the voice of god for deco, i.e. its fundementally wrong before you even get to your gas switch, there's no sense in arguing that other aspects of its profile are somehow "correct".
...

Hear hear. The voice of reason

 

[Clare]

Seems to me that we are arguing which is the best flavour of ice cream here*

Ratio deco has it's uses - and when I dive within a certain window it is a pretty good tool to use. The question is where is the window?

A 45 metre (150ft?) dive for half an hour is perfect for Ratio Deco. Push much longer or much deeper on one deco gas and it starts to get cumbersome and inaccurate (around the depth we would change the set point). Longer deco is not always better - particularly in deep stops and care must be taken on dives which are particularly short (deep) or long (shallow) to get these in the right region. It can be done with good understanding of the desired outcomes but for this Ratio deco must not be used as a blunt instrument - it requires more refinement that this.

To inform yourself whether the dive you are planning is within the window you can either rely on previous experience or use as much information from as many sources as possible to get ideas of loadings prior to the dive.

I dive very regularly in the 40 - 70 metre range (130 - 230 feet) and operate Ratio Deco in water (with a few tweaks) but prior to a new dive profile I use every bit of information that I can lay my hands on to play with deco, run scenarios, look at various failures and study loadings, gas use etc.

For this I use Decoplanner but I can also use V planner, peer experience and my own experience when looking at planning a dive. GUE does not ask me to be wedded to one way of calculating deco - far from it - it asks me to be a thinking diver who takes my safety and that of my team very seriously indeed.

Checking plans for dives which are on the edge of our experience curve in as many ways as possible is one way that I can try to D.I.R.

Good debate though guys - interesting reading.

*although everyone should know that is always chocolate

 

[cool_hardware52]

Nicely put Clare.


Tobin

 

[grazie42]

I re-read the RD-paper (threads like this one make me revisit my reasons for my way of doing things).
It suggests that you compare the RD-profiles with V-planner (+2), here is my comparison (mins are total deco time), I did this in metric so the figures in feet are rounded:
T1-range(?) 21/35 with 50%______V-plan +2__________RD______Diff
35m/120ft_________________________18mins_________15mins_____+3
40m/135ft_________________________25mins_________25mins_____+/-
45m/150ft_________________________32mins_________30mins_____+2
50m/170ft_________________________39mins_________35mins_____+4

T2-range(?) 18/45 with 50% +O2____V-plan +2_________RD_______Diff
55m/180ft_________________________45mins__________45mins_____+/-
60m/200ft_________________________56mins__________50mins_____+6
65m/220ft_________________________65mins__________ 60mins_____+5
70m/235ft_________________________74mins__________ 65mins_____+9
*I didn´t reset all my configs for this so the numbers on V-planner vary a bit depending on different descent/ascent-rates, last-stop depth etc but not significantly

Assuming I haven´t made a mistake somewhere or misunderstood something fundamental the above numbers seem to indicate that RD is a "bit" less conservative than V-planner (+2). In the "grand scheme of things" this is, IMO, not likely to make much of a difference though it does look like it gets continously more agressive the deeper you go which may be something to keep in mind if this is your tool...

I don´t think(/hope) this is anything new to those using RD but I thought it might help those "on the other side" see the actual differences to put this into context...

Another thing to keep in mind is that this is just the "bare-bones approach", I think everyone tweaks things a bit here and there (I know I do)...

P.S I agree about the chocalate

 

[rjack321]

I dive very regularly in the 40 - 70 metre range (130 - 230 feet) and operate Ratio Deco in water (with a few tweaks) but prior to a new dive profile I use every bit of information that I can lay my hands on to play with deco, run scenarios, look at various failures and study loadings, gas use etc.

So what would you consider a "new profile"? 5 mins longer? 30ft deeper or shallower?

For me, I am running ratio within the following boundaries:
21/35 or 18/45 BG
<30 min deco on 50%
130-160ft max

For 30/30 with real O2 deco (anything > than a 5 min cleanup) I start pulling out other tools. I still know the ratio approach for these dives, but: 1) I'm not as confident about doing the math in my head and 2) I don't have the personal experience with these dives to know my own boundaries.

Other tools =
buddies experience
decoplanner
Gap
my T1 notes
the ratio method pdf