Ratio deco

[Kevrumbo]

What is it and what does it look like when you use this method? Relying on your brain and being able to recalculate things on the fly sounds valuable

I haven't found any threads that do a good job describing what rd is and how it is done. Could someone give me the $0.25 explainer on this? Or just a link to some good materials. Thanks!

Take the online class at:
Ratio Deco - Unified Team Diving

Attached is an old monograph pdf on the method, and an Excel file of how to write your own program utilizing the algorithm.

 

[wrybosome]

Groups - Unified Team Diving

Why not pay $75 and learn it from the online classroom instead of the summary that someone might post on here?

Thanks for the link, though you're first bit of advice looked good too. What happened to that post???

 

[Reg Braithwaite]

Oh course, there are assumptions that go along with this, such as standard gases, proper familiarization with the decompression theory, ability to do mathematics underwater, and most importantly, knowing WHY you're doing what you're doing.

Great post, thanks. The only thing I'd question is whether Ratio Deco ("RD") necessarily implies Deco On The Fly ("DOTF"). I'd say that Ratio Deco uses a number of simplifying principles such that DOTF becomes possible, and then there is some larger set of practices such as certain flavours of DIR that teach divers how to calculate DOTF and not use a computer to plan the dive or dive the plan.

However, strictly speaking, I think it is possible to use Ratio Deco to plan a dive and then simply stick to the plan. Or use Ratio Deco with a computer as a backup. Or any number of other things. I guess I'm just trying to separate the concepts a little because to me it seems that Ratio Deco is just a piece of a larger set of practices that interlock and work with each other a certain way.

Does that make any sense? Or am I ranting and raving about nothing in particular?

 

[wrybosome]

Thanks kev i did want a look at the math!

 

[PfcAJ]

so you would use different baseline ratios for different depths and gas mixtures, then use rules of thumb to modify deco time? How do you what depths to do the stops at? I hope my questions aren't too stupid, just curious here.

These are good questions. Typically, you've got a 30fpm ascent speed to about 75% of your average depth, then it slows to 10fpm (or slower) to the first gas switch, then stops every 10ft for varying lengths of time (this is dependent on the bottom time, depth, and gas) till the next gas switch, wash, rinse, repeat. As you can see, dive planning becomes critical with these types of dives. Playing with some dive planning software will help clear this up.

I highly suggest a good decompression course before attempting any of this, as the consequences of botching it can be quite severe (nerve damage, paralysis, death, etc).

Great post, thanks. The only thing I'd question is whether Ratio Deco ("RD") necessarily implies Deco On The Fly ("DOTF"). I'd say that Ratio Deco uses a number of simplifying principles such that DOTF becomes possible, and then there is some larger set of practices such as certain flavours of DIR that teach divers how to calculate DOTF and not use a computer to plan the dive or dive the plan.

However, strictly speaking, I think it is possible to use Ratio Deco to plan a dive and then simply stick to the plan. Or use Ratio Deco with a computer as a backup. Or any number of other things. I guess I'm just trying to separate the concepts a little because to me it seems that Ratio Deco is just a piece of a larger set of practices that interlock and work with each other a certain way.

Does that make any sense? Or am I ranting and raving about nothing in particular?

No, you're on target. I don't use a computer, nor do a lot (all?) of the folks I dive with, so if you planned the dive and got delayed on the bottom by 10 minutes, you're back to DOTF or some sort of tables (this is why I don't use RD as a primary tool). I'm pretty shoddy at math on the surface, god knows what it would be like at depth! I feel that RD is a good piece of kit for my toolbox, but I reach for other tools first. However, I do reshape the ascent curve to one that favors more time at the gas switch stops.

 

[Sloth]

Take the online class at:
Ratio Deco - Unified Team Diving

Attached is an old monograph pdf on the method, and an Excel file of how to write your own program utilizing the algorithm.

Holy crap trying to use that spreadsheet made my brain explode! Is there a Video Professor CD I can order to figure that thing out?

I think I'll stick with my scuba math

 

[Doc Harry]

What is it and what does it look like when you use this method? Relying on your brain and being able to recalculate things on the fly sounds valuable

I haven't found any threads that do a good job describing what rd is and how it is done. Could someone give me the $0.25 explainer on this? Or just a link to some good materials. Thanks!

Thanks for asking this question, I had question, too.

 

[Kevrumbo]

Holy crap trying to use that spreadsheet made my brain explode! Is there a Video Professor CD I can order to figure that thing out?

I think I'll stick with my scuba math

Yeah well . . .just like anything, you get used to it when you get the hang of it. And this spreadsheet will only confirm your initial segment values for a particular Ratio Deco Schedule (i.e. 1:1, 1:2, min deco etc), as well as give you an estimate of your gas consumed: you have to shape the curve and enter in corresponding stop times of the dive profile on the spreadsheet for each depth yourself. . .

(In comparison, as much as the commercial/retail deco software like GAP, v-planner, deco-planner and others cost, of course you would expect a more user-friendly interface!).

 

[TSandM]

Ratio Deco is a curve-fitting exercise, born of the observation that decompression programs all generate a similar shaped profile, although the exact details may vary. A superb article about this (the one that initially piqued my interest in learning about decompression) is HERE, although you will have to register on TDS to read it. It was written by our own Doppler.

The rules are simple enough that one CAN utilize them underwater, but they are heavily dependent on assumed initial conditions -- i.e. standard gases, and dive times that don't exceed reasonable limits.

I highly recommend the online classroom on the UTD site, and also signing up for a webinar, when Andrew does another one. I did the RD seminar with him here in Seattle, and entirely apart from what I learned about RD, I learned a great deal about the history of decompression theory in general.

 

[LiteHedded]

I thought he meant of some sort of gue/dir/xyz fracas.

nah
I mean if you do it wrong you can get bent like a pretzel. some in this thread found out the hard way