What is Ratio Deco?

[CAPTAIN SINBAD]

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." I did not have the chance to understand this in great detail but from what I learnt, decompression times within recreational depths of 130 are calculated using average depth vs time for each dive?

Does anyone else have an idea what Ratio Deco is and how that works? I was extremely intrigued by this but I have not met a lot of people who will do away with dive computers and do math mentally for repeated multi-level diving.

 

[tbone1004]

wasn't there a Ratio Deco thread recently? like in the last few days?

Either way, it is relatively easy to understand, but the wikipedia article on it actually explains it quite well.

Ratio decompression - Wikipedia, the free encyclopedia

 

[CAPTAIN SINBAD]

Sure but I am interested in knowing what real divers think of it. Has anyone ever tried this and then decided, "No thank. I need to go back to my dive table or computer."

 

[tbone1004]

many go back to the computer for the convenience of it, but most of us do carry tables just in case and many of us do know how to use the ratio deco model. It is my contingency plan in case of a computer failure, or if the dive tables aren't agreeing with what I know to be the approximate deco obligations.

 

[decompression]

Min deco/ ratio deco are used by GUE and UTD. There was a large scale evaluation of ratio deco as an ascent strategy in comparison to a modified Buhlman algorithm last month in Spain.

 

[bradells]

Ratio/Min Deco (as per NDL diving) is used by technical organizations (UTD/GUE) for and easy way to remember how to get home safely (and to calculate your next dives NDL).

No remembering of tables (as long as you follow the rules ... Rule of 130 comes to mind with GUE)

In one of Dopplers books, he explains it fairly well, as well as going into Tech depths and decompression diving with examples using a version Ratio Deco.

There are also other DIR websites that can explain it as well (in the recreational realm).

In short, it's an observation of decompression theory, 'dumbed' down to easy to remember ascent profiles. MIN Deco is generally for 'NDL'/Rec diving, and Ratio Deco is decompression/technical diving.

Personally, Until I have a second computer/BT, I keep mine on a DSAT algorithm for recreational diving rather than diving it in Guage Mode, but still follow GUE MIN Deco based on my dive profile and use the more conservative ascent profile (which so far, has always been MIN Deco).


BRad

 

[CAPTAIN SINBAD]

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.

 

[Dr. Lecter]

It's a method that's only really reliable within a relatively short range of exposures and, as a certain mouthy Truk diving SB denizen can attest, a great way to bend yourself like a pretzel if you do the math wrong on ascent. It also requires standard gasses. Overall, it's good to know as a back-pocket resource and as a sanity check on plans, but it's not a universally applicable Jedi mind trick for deco.

 

[LiteHedded]

the problem with ratio deco is that it totally falls apart when the bottom times get longer. if you compare your ratio deco schedule to the algorithm and the algorithm wants more deco. your ratio deco table is WRONG

 

[PfcAJ]

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.

Ratio Deco isn't popular because the majority of agencies don't teach divers to use standardized gases. If you're flip flopping gases all the time, its tough to identify simple trends in deco times relative to depth and exposure.

Imo, it doesn't add much in complexity, and in same ways removes it since you kind of know what to expect before you even get into the water. Its quite easy, really, and it makes changing depths simple from a planning perspective. For instance, if the wreck I was planning on diving was at 150, but we moved sites because another boat was on it (whatever) and now its at 170, that's no biggie since with RD, I can easily replan the dive. It does break down as the dives get longer, however, so its not perfect.