Why do some agencies recommend using a bottom timer instead of a computer

[The Chairman]

Everyone has opinions and I am no one to say whether they are valid or not but people who do not dive ratio-deco normally over-estimate the complexity of the math involved.

No, that's not it at all. I believe you are over-estimating your ability to function while narced. As long as you stay within your comfort zone, you're fine. Get a little task overload and then mistakes, small/simple ones are made, which lead to larger issues and ultimately DCS. This isn't a 'hypothetical situation', but one that has played out time and time again. I know far fewer divers who use RD, but they comprise the bulk of the DCS incidents among my friends. Hubris tells you that you can do it, but reality tells a far different tale. Me? I'll stick with reality.

BTW, rather than telling us critics why we believe some protocol to be faulty, you should just ask us instead. I'll be glad to tell you why I think it's dangerous. No need to speculate there. Too many injuries over too few dives and divers. It's not a stable protocol.

 

[barth]

I also think using evidence of a Suunto Gekko going into error mode while on a decompression dive is simply beyond belief. That is exactly what you would expect when you use something for a task for which it was not designed. I would not argue against using a shovel to dig a hole by showing a picture of a teaspoon I bent while digging a hole with it.

You're missing the point. It was not a tech dive. There were 3 rootcauses for the gekko to be in error mode.

- I did analyse my tank at my car and set the right percentage of ean in my computer. When was in the water the software of my gekko had changed the% from 32 to 21 for safety reasons because the computer was already in the water it did not allow me anymore to change the %.

- I had the most aggressive setting at my gekko. But it is still conservative. A lot of people at scubaboard also tell not to buy a gekko because it's conservatism.

- The software thinks it is a safety or deco stop between 4,0 and 6,0 meter. If you do a stop at 6,2 meter it is not accepted. It also don't understand a stop at 3 meter depth.

We were doing a rec dive with ean32, max depth 30 meter, average depth 25 meter. Just like the hilma hooker at bonaire. We did plan the dive and we were doing stops at 3 and 6 meters of depth.


It was not possible to put the gekko in gauge mode because there is no gauge mode at the gekko. I decided to sell the gekko and to buy a uwatec tec 2g and put it in gauge mode.

At that point I already had hundreds of dives. It was in 2008 I think. Now ten years later i'm still using a computer in gauge mode.

But I don't consider myself as a tech diver. I'm doing dives with max 1 decogas and max 30 minutes of deco.

For that dives my software on my iphone is used for deco planning. My buddy is also planning that dive. We compare the plans and decide what deco we do. In my wetnotes there are tables, dives I did earlier that may also be usefully for my diveplanning.

Maybe when dives are getting more advanced I will use a computer. For now gauge mode is enough for me. But this thread was at basic scuba, my answer was just for rec dives and not for an advanced divecomputer. But just for a gekko or something like that.

 

[boulderjohn]

Everyone has opinions and I am no one to say whether they are valid or not but people who do not dive ratio-deco normally over-estimate the complexity of the math involved. I discussed RD with a few friends who are die-hard critics of RD and they had no clue how to actually do a dive on ratio decompression. Yet they were so opinionated and it made me wonder if you do not know a method then where is the criticism originating from?

So normally before talking about RD I like to give the critics a few parameters. Eg. You are diving U-352. The top of the wreck is 90 and the bottom is 115. How do you plan two dives a day using RD (or min-deco?)

A person who knows Ratio Deco will give you the answer in less than 5 seconds for both dives without consulting a table or a dive computer. Now if this person is also a critic of Ratio Deco then I will value that criticism as it is coming from someone who knows exactly what he is criticizing.

If the guy responds by saying WHA?? HUH???? Or "Let me get a computer so that I can spend not 5 seconds but 10 minutes to first determine the MOD of nitrox mix for that depth after which I will get my bottom time for the first dive and then I will need a computer to put in 60 minutes of a surface interval so that I can know my bottom time for the second dive and I cant believe the stupidity of people who try to do this mentally when computers can do this so much faster than the human mind and that is why I need 10 minutes while they do it in 5 seconds" then I am having this discussion with the wrong dude no matter how self-justified he feels holding a computer in his hand.

So what you are saying is that people should use an inferior deco plan because the math required to use it is not as hard as it seems and the potential to make a serious error using this inferior program is not as great as people think. Got it!

 

[boulderjohn]

As for doing math and other calculations while diving.....

deepadventurescuba.net/blog/detail/7

 

[barth]

As for doing math and other calculations while diving.....

deepadventurescuba.net/blog/detail/7

If you make 3 serious errors during a dive and you and your buddy don’t notice the errors you shouldn’t do the dive.

If you make 3 serious errors during a gas switch and you and you buddy don’t notice it there can also be a seriously problem.

Also when you and your buddy do a cave dive and make 3 serious errors with navigation.

I think it is wrong to ignore the fact that they shouldn’t do the dive. Training would be the solution, not buying more advanced equipment.

 

[boulderjohn]

If you make 3 serious errors during a dive and you and your buddy don’t notice the errors you shouldn’t do the dive.

If you make 3 serious errors during a gas switch and you and you buddy don’t notice it there can also be a seriously problem.

Also when you and your buddy do a cave dive and make 3 serious errors with navigation.

I think it is wrong to ignore the fact that they shouldn’t do the dive. Training would be the solution, not buying more advanced equipment.

They made errors that resulted in DCS. Without a computer in gauge enabling them to check the log, they would have sworn they had made no errors. These two had had a couple years of training prior to this. One of them was a few months shy of his Ph.D in computer science. They evidently did not have your Godlike diving skills, but how much training and mathematical education should they have had before attempting a decompression dive without a computer?

 

[The Chairman]

They evidently did not have your Godlike diving skills,

The real issue here is Nitrogen's effects on the cognitive process. It will amplify any tendency you have to forget and make mistakes. That you don't even realize it's happening is also attributable to excess N2. People expect a buzz from their "narcosis" and that's only in extreme cases. You start losing IQ points when you strap on the gear, more when you splash and you continue to lose them the deeper you go. You simply aren't on your "A" game mentally when you're below 66ft. Can you compensate? Maybe. Maybe not. Many people can "get away" with driving drunk. They are more lucky than skilled. Simple hubris is probably the one single biggest factor in DCS incidents. It's the "it can't happen to me" because syndrome.

 

[CAPTAIN SINBAD]

No, that's not it at all. I believe you are over-estimating your ability to function while narced.

See! That line alone in bold tells me that I am discussing this with someone who does not understand ratio-deco. The very reason GUE and UTD introduce helium in their standard gases shallower than mainstream agencies is so that you do not get narced. Diving while narced is a huge NO NO in their world.

So what you are saying is that people should use an inferior deco plan because the math required to use it is not as hard as it seems and the potential to make a serious error using this inferior program is not as great as people think. Got it!

Honestly? This is the criticism that I can relate to to some extent. When someone uses the term "inferior deco plan" then it shows that they have actually compared ascent curves with Buhlmann or VPM etc. Only two types of people will use the term "inferior deco plan" to refer to Ratio Deco.

1) Those who believe RD is inferior because of deep stops.

2) Those who believe that RD is inferior because it give you less and less decompression as the exposure time increases and after certain exposures you have deviated from all algorithms.

From our previous discussions on this issue John, I think you fall into both camps. Correct? As a skeptic of ratio deco, I have been in camp 1 but I had a discussion on deep stops with Dr. Simon Mitchell who you know is not a fan of Ratio Deco. I asked him how much more safer do you get when you skip the deep stop and add that time to the shallows? He said that the actual safety you create for yourself is so less that "it is not worth talking about." Isn't that what Dan_P wrote up there? To rephrase both Dan_p and Dr. Simon Mitchell let us put what the two of them agree upon this way.

"Ratio Deco enables you to instantly calculate bottom times and deco times in your head within a margin of error that is insignificant!"

Is everyone happy now? Also remember that RD can be personalized to your preferences so there is nothing stopping you from taking the time spent at deep stops and adding it to the shallowest stop.

2) Category 2 critics would be GUE's Bob Sherwood. I discussed Ratio Deco with him and his concern was not the deep stops. Just like Dr. Simon Mitchell and Dan_p, Bob Sherwood was also of the opinion that this deep stops vs shallow stops within the depths that we are talking about is not where any critic of ratio decompression should spend his energies. He mentioned that as exposure times progress, the ratios fall apart. Dude, this is where I stand on my own skepticism of ratio deco. If I have any fear of raatio deco then it is this one.

Is this a valid concern? So far the depths and exposure times at which ratios deviates from algorithms to the point where they would go from slightly less than optimum to "HOLY $H!T" are so long that you will run out of air before that becomes a concern. You are limited to 2 tanks and a single decompression gas at Tech 1 so it will be hard to stay down there in that configuration where ratios become an issue.

Having said all that, since computers have become so common, should we actually use ratio deco to REPLACE a computer or to SUPPLEMENT a computer? Tell me about it please

 

[The Chairman]

That line alone in bold tells me that I am discussing this with someone who does not understand ratio-deco.

Things I don't understand about ratio deco:

• Why bother?
  • There are better more effective tools
  • I don't dive to babysit my deco schedule
  • Too, too many hits
  • I've got better things to do with my life, like watch grass grow
• Why expose yourself to needless risk?
  • Too many cases of DCS among RD divers.
  • There is no study that condones RD
  • RD is based on anecdotal inferences and not science
• Why you feel the need to delude yourself and others?
  • Ratio Deco is a protocol that's based on inference not science
  • Ratio Deco presupposes that you can't make a mistake and get bent
    • ...and that computers are unreliable
  • Blindly following this protocol does not make you a better diver
  • Using more effective tools is not a bad thing
  • Hubris is not a good thing.

Here's what I do understand about Ratio Deco:

• It's defective
• It's dangerous
• It was born in arrogance
• There's absolutely no science behind it
• People get hurt using it
• It merits no further study when there are far, far superior protocols that work well.
  • No, I'm not going to drink your Koolaid with you!

 

[Diver0001]

If you make 3 serious errors during a dive and you and your buddy don’t notice the errors you shouldn’t do the dive.

If you make 3 serious errors during a gas switch and you and you buddy don’t notice it there can also be a seriously problem.

Also when you and your buddy do a cave dive and make 3 serious errors with navigation.

I think it is wrong to ignore the fact that they shouldn’t do the dive. Training would be the solution, not buying more advanced equipment.

"Barth", the point John is making here is that some ascent strategies are more prone to errors than others. Ratio deco has a large dependency on diver alertness, which is defacto more prone to errors than the calculations made by a computer. There have been many bends using RD due to "brain farts". One Scubaboard user, in fact, could have killed himself using ratio deco because of such a brain fart. His story is illustrative of the risks of "user error", as are the examples John mentioned in his blog.

Personally I can't even count the number of times I've been at the Albert Heijn and made a mental calculation of how much my groceries would cost only to be surprised at the cash register by how big the error in my mental math was. Granted, ratio deco doesn't require adding up long lists of numbers in your head but the principle is the same. A computer can quite simply do these things BETTER than we can, and not by a small margin. There is no getting around that.

Again I repeat what I said before, which is that ratio deco had a function in the time between -- let's say for the sake of argument 1990 and 2005 -- because in that period of time technical diving was becoming more popular but there were literally no adequate technical computers on the market. Since 2005, however, that has changed. The truly "faithful" RD users, have, in that time, not kept up with developments and are now arguing to apply a paradigm that is +/- 20 years out of date to a context in which it is no longer applicable.

R..