What is Ratio Deco?

[Kevrumbo]

That's an old wives tale. Put in 12/65 bottom gas and 21/35, 35/25 50%, and 100% as deco gases into decoplanner and run it. Then do the same with no helium. Deco time with no helium is always longer.

No "wives tale". Classic Buhlmann algorithm while it did first address potential precursor bubble nuclei/seeds/micro-bubbles, it does not not take into account the relative solubility/diffusivity of He vs N2. Another corroborating hypothesis:

From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:
Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.

Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.

(Oite Destroyer wreck today in Truk planned 60m ave depth for 50 min --last dives with storm/high winds coming this PM 21 Nov Fri here).

 

[Dr. Lecter]

anecdotal. and based on findings from friends who are decompression researchers. none of them use VPM

ask around friends who have taken hits and find out if they were using VPM or a schedule approximating it

I and most of the guys I do a lot of 80-100m CCR diving with out here are in the same situation. We were all using VPM and as our dives got longer and deeper, we increasingly found it didn't leave us feeling great without cranking up the conservatism way up past what our age/fitness levels would suggest (to at least +3 with a 70 or 75 GFS for me), and even then we'd get the occasional niggle.

After reading some of the newer research on GFs, especially the epic thread(s) on RBW about the NEDU deep stops trial, I think we've all gone to some flavor of shallow stop-biased GFs for what we do. I'm running 50/80, while others are doing stuff like 70/75 or 85/90...so far, so good.

 

[LiteHedded]

No "wives tale". Buhlmann algorithm while it did first address potential precursor bubble nuclei/seeds/micro-bubbles, it does not not take into account the relative solubility/diffusivity of He vs N2. Another corroborating hypothesis:


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(Oite Destroyer wreck today in Truk planned 60m ave depth for 50 min --last dives with storm/high winds coming this PM 21 Nov Fri here).

how do you account for the fact that if you run a buhlmann table with helium the deco time GOES DOWN?

 

[PfcAJ]

No "wives tale". Buhlmann algorithm while it did first address potential precursor bubble nuclei/seeds/micro-bubbles, it does not not take into account the relative solubility/diffusivity of He vs N2. Another corroborating hypothesis:


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(Oite Destroyer wreck today in Truk planned 60m ave depth for 50 min --last dives with storm/high winds coming this PM 21 Nov Fri here).

Put the gases in the program and see for yourself.

 

[boulderjohn]

I am very interested in the VPM discussion but feel it is a bit off topic. I am therefore going to start a new thread in the Tech area. I hope those who participated in it here will participate.

 

[Kevrumbo]

That's an old wives tale. Put in 12/65 bottom gas and 21/35, 35/25 50%, and 100% as deco gases into decoplanner and run it. Then do the same with no helium. Deco time with no helium is always longer.

how do you account for the fact that if you run a buhlmann table with helium the deco time GOES DOWN?

Put the gases in the program and see for yourself.

Post the results of your "programs" -and let's take a look. I don't use DecoPlanner or any other software nor what LiteHedded claims/believes are "Buhlmann Tables" (GF's/fudge factor on Classical Buhlmann implementation tables??)

---------- Post added November 20th, 2014 at 10:52 PM ----------

[Oite Destroyer, 57m ave for 50min on Air (max depth 62m in the Engine Room and down at the Screws); RD1:2 so 50min Eanx50 deco time -linear (no S-curve) 10min deco stops from 21m to 9m; 50min O2 deco time at 6m -10min O2 breathing with 5min backgas break, with a slow 1m per 2min ascent to 3m and an additional 20min O2 deco before finally surfacing. Deep Stops started at 42m for 2min and 2min every 3m up from there until 30m =>2min; 27m => 3min; 24m => 5min. Total run time over 3-and-a-half hours. Twin 11L conventional backmount doubles, and three 11L deco/stage tanks (all AL80's) for Air Bottom Mix, Eanx50 and O2. Also utilized UTD's wetsuit "cummerbund" waistbelt heater as needed because you get chilled hanging on deco for over two hours even in tropical 30deg C waters. . .]

 

[Taliena]

http://techdiving-network.de/wp-content/uploads/2014/05/Ratiodeco_et_al.pdf

I have not read all, but maybe do some german speakers like this link.

 

[LiteHedded]

I ran 270 for 60 minutes with and without helium. I assume you've tried this before you started pontificating about helium in buhlmann




dive is 100 minutes longer without helium

 

[Slamfire]

1. What is the basis for utd rd dictating deeper stops than most out there? I've always gotten a broad stroke answer that lacks any detail. The answer goes somewhat along the lines that it is to control bubble formation and growth. Then they go ahead and mention Wienke's and Yount's (vpm) work on bubble models as backup. Yet utd rd ends up having deeper stops than vpm and nobody can tell me why.

You say you're based on Yount yet your results don't comply with Yount. I know both Yount and Wienke have a vastly more robust scientifically analytical work behind their models than utd. So what is the basis for utd to claim superiority over them? The previously quoted utd journal has an entire section about the "the science of ratio deco". I see no evidence of the scientific method used to produce rd anywhere in that section.

2. Using vpm, if I do go ahead and start the stops as deep as utd rd dictates, I will have to do a few more mins of shallow stops than utd dictates. This is the "fundamental disadvantage" of buhlmann gf-- "unfairly" penalizing helium. But I am not using buhlmann gf. This is vpm. Why? Again, a detailess broad stroke answer. Helium is not soluble therefore you can ignore helium. Great! let's use heliox without any nitrogen and ignore shallow stops altogether.

 

[Kevrumbo]

I ran 270 for 60 minutes with and without helium. I assume you've tried this before you started pontificating about helium in buhlmann


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dive is 100 minutes longer without helium

For your hypothetical "Hypoxic 10/00/90 Bottom Mix", you better have 100 min more (!) . . .

Let's just compare "apples-to-apples" on the 10/65 Trimix profile above which shows over 300 min deco time IIRC:

RD1:4 schedule for 10/70 mix at 81m/270' for 60 min comes out to 81min for the O2 & Eanx50 (or 50/25 deco triox) =>round to 80 min. So the 35/25 triox stops total 40min, and the 21/35 stops total 20min. Total Deco Time: 80+80+40+20 equals 220 min, plus 3 min Deep Stop at 60m and 2 to 3min to go 9m-per-min ascent from 81m to 60m.

So comparing Ratio Deco to your DPlanner 10/65 deco times: 225 to 308 minutes respectively. So yes I would claim ("pontificate" as I was taught in AG's RD Class over eight years ago) that Buhlmann Algorithm penalizes you with extra deco time with the use of high Helium mixes -roughly 35% more deco time.

(But I would now use the Buhlmann total deco time with additional O2 time as needed if I did this dive here in Truk on Deep Air [PPO2/CNS & END/narcosis/CO2 retention Work-of-Breathibng would be extremely harzardous & dangerous] and Eanx36, 50 and O2. . .)