What is Ratio Deco?

[lowviz]

I had the pleasure of chatting with a UTD instructor yesterday. A very knowledgeable fellow. He said that UTD/GUE divers do not use dive computers. They use a bottom timer and follow a method called "Ratio-Deco." ...//...

Please suffer me just one question. Is this actually a true statement IRL on "big" dives? I mean for real, who does this?

All "DIR" types I've been exposed to dive electronics. Yes, they all can bail on RD. RD seems a bit "edgy" to me. I bail on the most effective use of ALL my remaining gas. I almost never have any issue. Big whoop, so when I *think* I do, I spend way too much time in the "think about it chair" recovering from a problem.

 

[PfcAJ]

Please suffer me just one question. Is this actually a true statement IRL on "big" dives? I mean for real, who does this?

I've never once used a computer for a deco dive. Bottom timer, avg depth, and tables only.

 

[ktomlinson]

I've never once used a computer for a deco dive. Bottom timer, avg depth, and tables only.

Why do you think that is the optimal configuration for you to conduct deco dives? Do you believe carrying a computer is a hazard or just unnecessary?

 

[lowviz]

Ah, the exception that proves the rule.

Pretty much figured that of you. But how many others?

 

[Diver0001]

Oh... believe me, I get it.



R..

 

[PfcAJ]

Why do you think that is the optimal configuration for you to conduct deco dives? Do you believe carrying a computer is a hazard or just unnecessary?

I'm not going to do what the computer says anyway. I'm going to redistribute stops, put in gas breaks, start counting bottom time when I switch to bottom gas, all sorts of stuff. I can glance at a table and know "alright, if I spend another 20mins at depth, what kind of deco am I looking at" and compare different depth/time profiles super fast and easy. No need to remember to switch gases on the computer, either.

 

[Kevrumbo]

That's the whole point . . . RD ought to give you almost the same profile as Buhlmann with gradient factors and an oxygen window kludge, because that's how it was derived. It doesn't do that on really extreme dives, but within the boundaries of the "typical" staged decompression activities divers do, it works pretty well. UTD RD has some very deep stops that DON'T show up on a DecoPlanner or Gap profile, which is one of the differences. In addition, the 50% deco on UTD RD is S-shaped, whereas GUE has gone to linear pragmatic. I personally doubt it matters.

I watched the video on the Italian project, and although the details of the experimental protocol aren't discussed, the broad outline of the experimental design seems sound. The one thing that was unclear was whether all divers in the project would dive both profiles, which is very important, as we know there are significant individual differences in the tendency to bubble after dives. The video says the project will take (or has taken; it's unclear to me which) four years, which would suggest a good number of dives, which would be great. Many of the studies in humans suffer from very low numbers, which reduces the power to detect a difference.

I know that's the whole point Lynne -if the Petrel numbers agree what I calculate on the fly with RD, then I have a "checksum" so to speak (and won't come up 30% less than the optimal deco run profile like I did six years ago) -then apply the Deep Stops & S-Curve per RD and add extra O2 time as needed. (Also have enough O2 to do an IWR contingency for 30 to 60 minutes at 9m if with a very slow 0.1 m/min ascent to surface).

Again a disclaimer; diving primarily Deep Air and EANX30 bottom mix for two dives a day with minimum 3.5 hour surface interval for over 4 weeks is not within the parameters of the UTD requirements for implementation of RD.

 

[coldsmoke]

Ah, the exception that proves the rule.

Pretty much figured that of you. But how many others?

You'd be surprised I would guess.

I rarely dive with anyone using a computer - purely recreational divers and those needing a larger/illuminated screen aside.

Why do you think that is the optimal configuration for you to conduct deco dives? Do you believe carrying a computer is a hazard or just unnecessary?

Other than reconciling different profiles within the team because of different computers there's no real hazard in them, they're just completely unnecessary.

Find something else to spend $1,000 on.


Hunter

 

[TSandM]

Nobody I know is using a dive computer to run their staged decompression dives. Most people aren't using any kind of device that gives them that information -- most of my friends are using something like the Xen bottom timer. I use an X1 because I love the OLED display. When I first got it, I was using a demo device, and I was asked to allow the V-planner software to run. I found that it agreed quite well with what I was already doing, so I have never disabled it. But the rare technical dive I do is planned using RD (slightly different from UTD's) and executed that way.

 

[Slamfire]

I'm not going to do what the computer says anyway. I'm going to redistribute stops, put in gas breaks, start counting bottom time when I switch to bottom gas, all sorts of stuff. I can glance at a table and know "alright, if I spend another 20mins at depth, what kind of deco am I looking at" and compare different depth/time profiles super fast and easy. No need to remember to switch gases on the computer, either.

I use a Predator and very often I don't do what the computer says. As long as you stay below the deco ceiling, you can redistribute stops to your leisure. And even when if you break the deco ceiling it will not block you out. It might not be healthy to you, though. It will recalculate in realtime any deviation from the profile it is suggesting -- without hitting you with stupid, unpredictable penalizations that are outside the algorithm that you came to know in Decoplanner or Vplanner. Switching gases takes less than a second.

For inexperienced readers: I am not promoting deviations from a safe ascent behavior. Proper dive planning is more than just blindly following computer instructions. Refer to your training and instructor if you have any doubts.