Deco with too less air, options from the book

[crpntr133]

Thanks Rainer!! Discussing deco on the internet is just plain crazy. Yah, the basic idea is possible but other than that, not for me. From what I am seeing RD is more of a "tool" rather than a theory. Am I correct?

 

[Rainer]

Thanks Rainer!! Discussing deco on the internet is just plain crazy. Yah, the basic idea is possible but other than that, not for me. From what I am seeing RD is more of a "tool" rather than a theory. Am I correct?

It's NOT a theory about decompression. Before we were taught RD, we were made intimately aware of many true decompression theories. We played with a lot of programs and cut a lot of tables. Then RD was introduced. It's a formalized system of observations concerning decompression theories that has been formulated for use by divers in the water. It's definitely a sort of tool.

 

[Chatterton]

Guys,

It appears I do understand Ratio Deco, at least enough for me to know if it is for me or not. Thanks for taking the time to explain it. If it works for you, go with it. It simply won't work for me.

When it comes to decompression diving "cheaper" (or even expensive), are not my determining factors. I need utility. If I can't afford the right tool for the job, I don't do the dive.

Most of the time, I am trying to accomplish something while I am in the water, so I am already engaged in my dive and I don't need any added incentive. My dive computer can flood, fail, or otherwise crap out, this is true, but you are depending on a timer and depth gauge with "depth averaging", so we are both unfortunately somewhat dependent on technology that can fail us. As for the quality of tables in a dive computer, that depends on the computer, and the diver.

The fact that you educate yourself so thoroughly in decompression theory is admirable, and you undoubtedly know more about theory than the average Deco Joe. However, I don't understand why a table kept in your memory is superior to either a calculated written table (or set of tables) carried by the diver, or a dive computer? To me, it seems gimmicky? Sorry.

Ratio Deco does not do your dive for you. Neither does any table, or dive computer. We need to interpret the information these tools give us, and we are the ones who make the decisions on how, and when we ascend. I want as much info as possible, especially in an emergency.

For instance, let us say I am involved in the rescue of another diver from depth. I am going to have my hands full. The last thing I personally would want is the added responsiblity of an ascent profile that is kept in my head, which I expect would already be full. I also know I can't afford to screw up and get bent, as then the surface support has two divers in trouble, not just one, and then resources are unecessarily strained. I have already had this experience and know how it goes. If this sort of thing only happened to me every thousand dives or so, it would already have happened more than once.

As I have said before, we do not all dive for the same reasons. If you guys are happy doing what you are doing, I congratulate you for finding something that works for you. Not everyone does. As for me, my experiences underwater have shown me that I really need to have something more than Ratio Deco for myself considering the way I dive and to tell the truth, for those same reasons I would also want the same for my family and friends (which got us into this discussion in the first place).

Cheers

JC

Sorry if I misunderstood your earlier warnings against using RD. I had assumed you had some understanding of it before making these claims. As for your questions:

(1) Advantages: It's much cheaper (free), forces a diver to keep constantly engaged during the dive, won't lock me out, won't leave me high and dry in an emergency, is running what I consider a better algo than most computers, affords (along with standard gases) feedback about personal conservatism, has all similarly trained teammates running the same algorithm, and won't fail due to low battery or flood.

(2) My brain.

Again, I'd be happy to discuss any possible misunderstandings you have. You might not have any, I don't know. Why don't you go ahead and tell me what you understand RD to be?

Cheers.


Edit: Let me also just add, like orange_diver, I don't give one hoot how others choose to dive (as long as it doesn't affect me). If that means rocking five dive computers, go for it. That said, I *am* curious why people suggest others avoid certain strategies as you did earlier, John.

 

[Rainer]

Again, I'm sorry to see that you won't state what you believe RD to be. Sort of odd.

To clear up some misconceptions:

I assume ALL of us are diving with some incentive. I don't think that's a difference.

We also aren't using a gauge to do the depth averaging. We do that ourselves (yes, using the gauge to tell us our current depth). The point is, we're keeping a running total, so if the gauge were to die, we could still plan and execute our deco, no electronics needed.

Your concern of a "full head" is reduced with practice. I assume ER docs don't forget all of med school when someone comes in after an accident. That same doctor probably didn't have that bandwidth in med school. Using RD successfully does take practice. Many divers are successfully using it. Personally, I know many more divers bent on computers than RD. I'm sure that's the case for you, too.

Also silly to suggest any of us can afford to get bent. Weird.

Your "gimmicky" comment suggests you don't understand RD. About what I imagined. If you care to actually learn, take a look at link I posted earlier. If not, that's cool. Like you, I really don't care what others do if it works for them. Always nice to educate yourself, however, about alternatives.

Thanks for posting!

Guys,

It appears I do understand Ratio Deco, at least enough for me to know if it is for me or not. Thanks for taking the time to explain it. If it works for you, go with it. It simply won't work for me.

When it comes to decompression diving "cheaper" (or even expensive), are not my determining factors. I need utility. If I can't afford the right tool for the job, I don't do the dive.

Most of the time, I am trying to accomplish something while I am in the water, so I am already engaged in my dive and I don't need any added incentive. My dive computer can flood, fail, or otherwise crap out, this is true, but you are depending on a timer and depth gauge with "depth averaging", so we are both unfortunately somewhat dependent on technology that can fail us. As for the quality of tables in a dive computer, that depends on the computer, and the diver.

The fact that you educate yourself so thoroughly in decompression theory is admirable, and you undoubtedly know more about theory than the average Deco Joe. However, I don't understand why a table kept in your memory is superior to either a calculated written table (or set of tables) carried by the diver, or a dive computer? To me, it seems gimmicky? Sorry.

Ratio Deco does not do your dive for you. Neither does any table, or dive computer. We need to interpret the information these tools give us, and we are the ones who make the decisions on how, and when we ascend. I want as much info as possible, especially in an emergency.

For instance, let us say I am involved in the rescue of another diver from depth. I am going to have my hands full. The last thing I personally would want is the added responsiblity of an ascent profile that is kept in my head, which I expect would already be full. I also know I can't afford to screw up and get bent, as then the surface support has two divers in trouble, not just one, and then resources are unecessarily strained. I have already had this experience and know how it goes. If this sort of thing only happened to me every thousand dives or so, it would already have happened more than once.

As I have said before, we do not all dive for the same reasons. If you guys are happy doing what you are doing, I congratulate you for finding something that works for you. Not everyone does. As for me, my experiences underwater have shown me that I really need to have something more than Ratio Deco for myself considering the way I dive and to tell the truth, for those same reasons I would also want the same for my family and friends (which got us into this discussion in the first place).

Cheers

JC

 

[TSandM]

I think it's great that someone with Mr. Chatterton's incredible experience in decompression diving is participating in a discussion like this. I think there are very few people on this board who have done the amount of deep, staged decompression diving that he has done.

I also suspect (without any data, it's true) that the majority of people doing staged decompression diving are cutting tables and using some type of multi-gas computer as a synergistic strategy for managing their deco. People using Ratio Deco are in the minority, even among DIR divers, I suspect.

I don't do staged decompression diving, but I have read extensively on the subject, and I have taken the Ratio Deco class. Ratio Deco is a curve fitting exercise. Its biggest utility is its flexibility; it's easily adapted to dives where you don't quite end up where you wanted to go, or staying as long as you thought you would. It's far more easily amended than tables, where you may only have cut one or two contingency plans. Ratio Deco is valid, within the assumptions made (standard gases and certain setpoints) because it has been fitted to the curves produced by other decompression models, after those curves have been adjusted for certain beliefs held about the behavior of gases and bubbles.

It may well be that, in the world of East Coast wreck diving, where the objective is known, the profile is square, and best mix is a common approach, that using decompression programs and a computer works better for a lot of divers. There is nothing wrong with that. Ratio Deco is not revealed truth. It's a tool that works very well for a lot of divers. Mr. Chatterton does not need to adopt it to dive safely -- I think he's already proven that.

I don't idly give honor to people, just because they have been in the water more than I have, but I think John Chatterton is someone who has done some amazing diving, and I suspect there are very few of us on SB who have the credentials to chide him on his choice of decompression strategy.

 

[Rainer]

Yawn (again), Lynne. Your grand-motherly post aside, everyone here is an adult. No one is "chiding" anyone else.

I respect John's choice of how he dives (and he seems to do the same for others). I also have GREAT respect for the dives he's done.

That said, he seems to have some misunderstandings about RD. His "gimmicky" comment borders on plain silly. Plenty of people are doing some really big dives using RD. It's not a gimmick. That said, it's clearly not for everyone.

 

[Shearwater]

Since you are the one promoting RD, please tell us about it.

I have certainly heard of it, and I've seen three people dive it over the years.

My impression is that it depends on controlling some of the variables like gas or depth profile.

I dive rebreathers, and I can't find any information on the web about how to use it on a rebreather and how to use it for multi-gas bailout profiles that would allow me to deco out using any gases that a team member has with them.

So rather than someone who knows almost nothing about it talking about it, why don't you tell us how it works.

I'm always interested in learning.

Bruce

Again, I'm sorry to see that you won't state what you believe RD to be. Sort of odd.

To clear up some misconceptions:

 

[JeffG]

Since you are the one promoting RD, please tell us about it.

I have certainly heard of it, and I've seen three people dive it over the years.

My impression is that it depends on controlling some of the variables like gas or depth profile.

I dive rebreathers, and I can't find any information on the web about how to use it on a rebreather and how to use it for multi-gas bailout profiles that would allow me to deco out using any gases that a team member has with them.

So rather than someone who knows almost nothing about it talking about it, why don't you tell us how it works.

I'm always interested in learning.

Bruce

Ratio Deco is a rules based system used to generate a deco schedule. The one taught by GUE and UTD is based on using their standard gases. (Note: you could create a RD air schedule if you so wanted.)

There are no theoretical "compartments". The rules basically state..if you do X bottom time...you need to do X mins of deco. If you go deeper than depth X...add 5min of deco time...etc etc

That deco time is split into 10 ft stops.

It generates a curve that approximates the curve generated by most Deco software packages out there.

Advantages: Understanding the rules, allows the diver to adjust deco "on the fly".

(I went 10 ft deeper than my plan...due to the interesting part of the wreck being deeper)...so I need to add some time to my deco. I know this upfront and before I actually do it. Most computers don't give you the consequences of your extra depth/time until you hit the deco stop.

Disadvantages: Only works in a range of depth/time. The closer you get to the outer boundaries, the greater the difference between the RD curve vs a software generated curve.

 

[TSandM]

If anyone is interested, THIS article by Steve Lewis on The Deco Stop (note: if you aren't a member, you will have to register to read the article) is a very good discussion of the thinking that leads to a Ratio Deco approach to decompression.

 

[Rhone Man]

There is one thing I don't understand about RD. If you are spending about $20,000+ on Tec gear (see other thread here), and about $250 for a trimix fill, why try and save a few hundred bucks on a computer (or better yet, two) at the expense of extensive task loading and increased risk of human error? Isn't using personal arithmetic (with a huge amount of rounding up and down) rather than deco software and dive computers siding with Luddites? Everything I have read on RD admits it is not perfect for all scenarios, but works well in most scenarios. Unless you're wedded to a particular philosophy "works well in most scenarios" is probably not what you want.