Ratio deco #1

[limeyx]

Sure we do: the one that DecoPlanner assumes. That's what RatioDeco intends to envelope, no?

Whether or not that has anything to do with reality is a different discussion.

For some profiles it's close. For some way off.
For "The Pit" Buhlman I think wanted 1200 mins of deco (or 950 something if you moved the O2 stop to 25 feet which is where the habitat was)

The actual deco was less than 1/2 of that (admittedly the divers were on CCR, but thats not going to account for such a vast difference)

 

[Blackwood]

For some profiles it's close. For some way off.

Agreed, for reasons stated earlier in this thread. I still don't understand Andrew's Pit profile; it exhibits exactly the opposite of what I'd expect to see: ratio deco calling for way LESS deco for a long bottom time. Admittedly I've never run 5 hour profiles, nor CCR profiles (though I'm betting his was low PO2). I have run 2 hour OC profiles, though, and Ratio Deco gets obscenely punitive.



Richard disagrees and maybe he knows something I don't, but it has always my understanding (supported by at least one post-GUE/pre-UTD/in-person ratio deco class with Andrew and Joe) that the setpoints were originally derived to approximate the total deco obligation as computed by deco planner for dives using the standard gases.

Obviously not the profile, but let's not forget what the OP asked for (blah blah blah blah "spit up your deco time...").

 

[ucfdiver]

Richard disagrees and maybe he knows something I don't, but it has always my understanding (supported by at least one post-GUE/pre-UTD/in-person ratio deco class with Andrew and Joe) that the setpoints were originally derived to approximate the total deco obligation as computed by deco planner for dives using the standard gases.

It says it right in the UTD slides that it's a combination of VPM/Buhlman

 

[PfcAJ]

I love it. No one really knows what it approximates. I think one thing, you think another, and someone else thinks something different all together.

And this, ladies and gents, is why I use tables and remove the confusion.

 

[limeyx]

I love it. No one really knows what it approximates. I think one thing, you think another, and someone else thinks something different all together.

And this, ladies and gents, is why I use tables and remove the confusion.

I think you are making too much out of those comments.

I have used nothing but ratio deco for over 800 dives up to 270 feet deep, and never had a problem figuring out what to do.

On a recent trip, I used the time the other guys spent writing down their 8 contingency plans to study the photos of the wreck we were diving and make a plan of what we wanted to film.

When RJack and I showed up to a wreck that was 25 feet deeper than expected we said basically "huh, we'd better do a bit of a shorter dive and reserve some more gas to get our butts home safe" and then went diving.

This isn't rocket surgery, although I will freely admit I am still a novice in applying these techniques to these longer bottom times, mostly because I cave dive in Mexico where it's much less an issue so I don't need to worry about it.

 

[TSandM]

Read Steve Lewis's (Doppler's) essay on the shape of the curve on TDS. It really doesn't matter what software you use; all of them will produce a very similar shape to a profile. The precise values at each data point aren't important, but the shape of the curve is. Whether you use a Buhlmann-based program or a bubble model program, the shape will be similar, although the bubble model will ascend a bit more slowly and spend more time in the intermediate stops.

The fact is that they all "work", in the sense that there are people out there doing significant dives using any of them and coming home whole. RD is a simple computation that you can do in your head, that roughly approximates the general shape of a decompression profile generated by any number of programs. RD as currently taught heavily emphasizes the deep portion of the deco, and I think there are accumulating some reasonable data that that may not be desirable, after all. And not all users of RD start the stops as deep as Andrew teaches, or hold them as long as he says.

Rick Murchison has it right: Decompression is akin to measuring with a micrometer, marking with chalk, and cutting with an ax. Any time you do a staged decompression dive, you are experimenting with your own body; keep careful notes. RD is no better and no worse than anything else out there to plan deco, but it's considerably easier to use. My guess is that nobody's program really "knows" what to do with 5 hour long 50 foot dives.

 

[ucfdiver]

The fact is that they all "work", in the sense that there are people out there doing significant dives using any of them and coming home whole.

I think people marketing a lot of these classes realize that there's a certain amount of wiggle room and make mountains out of mole hills in an effort to exaggerate things and sell classes.

I wish a whole lot of these theories about modifying tables could be better addressed. I know there were a series of Doppler tests done at Ginnie where VPM/Buhl/Ratio showed no trends in bubbling post dive. Deeper/Longer dives would be better, but it's hard to find divers doing them who are willing to wait a few hours to have tests run.

 

[PfcAJ]

I think you are making too much out of those comments.

I have used nothing but ratio deco for over 800 dives up to 270 feet deep, and never had a problem figuring out what to do.

On a recent trip, I used the time the other guys spent writing down their 8 contingency plans to study the photos of the wreck we were diving and make a plan of what we wanted to film.

When RJack and I showed up to a wreck that was 25 feet deeper than expected we said basically "huh, we'd better do a bit of a shorter dive and reserve some more gas to get our butts home safe" and then went diving.

This isn't rocket surgery, although I will freely admit I am still a novice in applying these techniques to these longer bottom times, mostly because I cave dive in Mexico where it's much less an issue so I don't need to worry about it.

True, its not brain science. But everyone seems to have a different idea of what it really is. Just strikes me as odd. And everyone thinks they are right. Well that can't be, can it?

I don't write down anything, though. That would be silly. I made some tables with Excel and deco planner for a whole host of dives (everything from 80-210ft, with times from as low as 40mins to as much as 140mins at depth).

 

[ucfdiver]

True, its not brain science. But everyone seems to have a different idea of what it really is. Just strikes me as odd. And everyone thinks they are right. Well that can't be, can it?

I don't write down anything, though. That would be silly. I made some tables with Excel and deco planner for a whole host of dives (everything from 80-210ft, with times from as low as 40mins to as much as 140mins at depth).

I did the same. I cut tables that have required gas (in psi) for deco, so I know if I drop my bottle with 2200, __ is my max deco, no math, quick glance at the tables. I'm not doing deep stuff, but I would have room for it on a single page for most any dive I can really imagine.

 

[Blackwood]

And everyone thinks they are right. Well that can't be, can it?

Nope. But I can be right. :mooner: