What is Ratio Deco?

[lowviz]

... sweet spot for gue's two versions of RD ...

Thank you, now I understand. Yes, works just fine that way. The same thinking would work for any depth range, or even any bottom time, if you limited the range that you are approximating [-]by changing[/-] and change the ratio to fit that range.

 

[Kevrumbo]

Plug the numbers into your deco software of choice and fiddle with it till it doesn't line up. It certainly diverges from 30/85 at around 40mins at 300ft (to the tune of about a half hour of o2 time).

For shorter BTs, it works fine. For longer stuff, not so much.

For 90m/300' @40min, use the Ratio Deco 1:4 schedule; The O2 segment is 36% of the adjusted Bottom Time multiplied by four (RD 1:4 schedule), so 36% of 40min multiplied-by- 4 equals 57.6 => round it up to 60 miniutes for the O2 segment.

So the Eanx50 (or 50/25 triox) deco stops from 21m to 9m would also total 60min; the 35/25 triox deco stops from 36m to 24m total 30min; and the 21/35 triox stops from 57m to 36m total 15min. If you add an additional intermediate deco trimix 18/45 for the 72m to 60m range, this would total 8min.

First deep stop for 1 min at 69m, and every 3m above that to 45m where it becomes 3min until you reach your intermediate deco gas switch ranges above. . .

 

[PfcAJ]

Did you pull that out from the text you linked or somewhere else? Because Buhlmann calls for almost 90mins of o2 time for that dive.

 

[Kevrumbo]

Did you pull that out from the text you linked or somewhere else? Because Buhlmann calls for almost 90mins of o2 time for that dive.

From AG's original article linked above. Also again remember that classic Buhlmann penalizes you with extra deco time for high Helium mixes (in this case either 12/60 or 10/70 trimix for 90m/300' working depth) because the algorithm doesn't take into account the greater diffusivity and lower tissue solubility of Helium compared to Nitrogen.

 

[abnfrog]

Interesting! So are you able to get as much bottom time per dive with Ratio Deco as you get with a conservative dive computer? And ... does using Ratio Deco involve significant task loading in terms of mental calculations? There must be a reason why it is not the most popular way to dive across the industry.

as dr lecter says its really no the be all end all .........plus even gue doesnt totally stand behind it

 

[LiteHedded]

From AG's original article linked above. Also again remember that classic Buhlmann penalizes you with extra deco time for high Helium mixes (in this case either 12/60 or 10/70 trimix for 90m/300' working depth) because the algorithm doesn't take into account the greater diffusivity and lower tissue solubility of Helium compared to Nitrogen.

and AG doesn't take into account the growing number of folks getting bent on VPM...

 

[boulderjohn]

and AG doesn't take into account the growing number of folks getting bent on VPM...

Do you have any links to info on this? (I am not challenging what you said---I am interested.)

 

[PfcAJ]

From AG's original article linked above. Also again remember that classic Buhlmann penalizes you with extra deco time for high Helium mixes (in this case either 12/60 or 10/70 trimix for 90m/300' working depth) because the algorithm doesn't take into account the greater diffusivity and lower tissue solubility of Helium compared to Nitrogen.

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.

 

[LiteHedded]

Do you have any links to info on this? (I am not challenging what you said---I am interested.)

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

 

[PfcAJ]

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

Can confirm anecdotes and deco researcher friends' recommendation to use Buhlmann.

I'd really like to get my hands on the NEDU probabilistic model, but I don't think that's in the cards