Riding Blind with your DSMB reel

[_Ralph]

'First time caller, long time listener'

Pete, John, AJ

I know which RD AJ is talking about.

Pete/John, are you talking about the 'algorithm must be wrong' RD or the 'follows/approximates the algorithm' RD?

Both are called "RD" but both are not the same ....

_R

 

[DevonDiver]

Your supposed scenario implies you can not read your bottom timer. Are you planning on counting each second?

"One-one thousand, Two-one thousand, Three one-thousand...".

Yes, I would if I had to. For shorter deco it's entirely achievable ... a bit like counting paces to measure distance when night navigating in the military.

Tedious, but workable... but nonetheless superceded by relatively cheap electronics.

 

[JohnnyC]

The idea that divers got bent "following" ratio deco, when they didn't follow ratio deco, is pretty tenuous. Ratio deco is a strategy for decompression, and it requires actually following that framework. If a diver is unable to follow that strategy, whether it's lack of mental acuity when doing calculations under the effects of nitrogen narcosis, lack of understanding of the system and employing it incorrectly, or being incapable of following the guidelines that make up the framework in which ratio deco works, is not the fault of ratio deco. In fact, every time I've heard someone who actually uses it regularly speak on the subject, they are very specific in pointing out that it was only designed for, and only works, in specific instances with controlled parameters. Once you start straying from the protocol, it all goes to hell and you're on your own. Blaming ratio deco for divers getting bent, when they don't actually follow ratio deco as designed, is like blaming a car for an accident because it's possible to exceed the speed limit, or blaming a computer when a diver ignores said computer....

That being said, considering the current market offerings I see no need to calculate deco on the fly. It's nice to understand the ratio for shallow deco dives, say 45m or less, for a half hour or less, and it works well in that regard using standard gases. However, again, it's a strategy that only works within the framework for which it was designed. Outside of that, it gets wonky. Trying to shoehorn wonkiness into a plan when there are better tools available is just asking for trouble. I have no problem running a "lite deco" dive with nothing but a bottom timer and ratio deco, and honestly probably over deco when it comes to it, but it is what it is. If i'm doing something long or deep, OC or CC, I'm definitely relying on my dive computer as a sanity check to the dive plan.

The nice thing about say, a Shearwater product, is that you can very easily adapt the technology to the type of diving you do, and realistically, if you can afford to do serious decompression dives, it's not outside of the realm of possibility that you will own a primary, and redundant, full fledged dive computer, for both. In the case of ratio deco, owning a computer (or two), sort of precludes the use of ratio deco in the type of diving I do. However, knowing that strategy is just another tool in the box that you can rely on if necessary.

That being said, I don't ever plan to lose two computers, two masks, my entire deco plan, my buddy, the dive boat, all my deco gas, and my knife while i'm being circled by a pack of ill-tempered sea bass..... I also don't plan on having to count minutes and knots on a spool as part of my dive plan, and I dive in such a manner that the odds of that actually occurring are probably less than being eaten by said sea bass.

 

[boulderjohn]

The idea that divers got bent "following" ratio deco, when they didn't follow ratio deco, is pretty tenuous. Ratio deco is a strategy for decompression, and it requires actually following that framework. If a diver is unable to follow that strategy, whether it's lack of mental acuity when doing calculations under the effects of nitrogen narcosis, lack of understanding of the system and employing it incorrectly, or being incapable of following the guidelines that make up the framework in which ratio deco works, is not the fault of ratio deco.

Look carefully at what was written. What was written is that it is too easy to make a mental mistake. If the system relies on the human brain to make the necessary calculations, and if people with mathematics related Ph.Ds do not have the "mental acuity" to use the system accurately, then the system is flawed.

BTW, of the 8 people I know who got DCS using Ratio Deco, those are the only cases in which we were able to identify a mental error. In the other 6 cases, we had no computer logs to see if they made mistakes. Maybe they did. maybe they didn't.

 

[The Chairman]

Pete/John, are you talking about the 'algorithm must be wrong' RD or the 'follows/approximates the algorithm' RD?

I didn't know there were two... the problem doesn't lie in the algorithm. It lies in the diver trying to keep up with that while dealing with narcoses and other distractions. It's also an oversimplified approach to decompression.

 

[JohnnyC]

Look carefully at what I wrote. If they are incapable of using the system as designed, it's not the fault of the system. Likewise, if they are incapable of interpreting the data on a dive computer, it is not the fault of the dive computer. If they got bent diving a Petrel would you say the same thing? Having a Ph.D does not preclude someone from making mistakes. Doctors do it all the time. You know they still leave things inside surgical patients? Even with checklists. You know what's never wrong, the checklists. You know why? Because they don't close the patient up until the checklist is complete. They STILL leave stuff inside of patients.

The idea that your friends are infallible is a TERRIBLE argument against a system. Literally the worst argument you could possibly make. Wes Skiles is a perfect example of the same type of argument. I also have a friend with a Ph.D in mathematics, in this case computational mathematics. He can't do multiplication in his head half as well as a 3rd grader, but he does fantastic work with data coming from satellites researching post-Kuiper Belt objects for the U of A... Your friends screwed up, they got bent. They did not utilize the system as designed. End of story. If they cannot use the system as designed, that's their fault, not the fault of the system. I get it, you'd rather blame a system than your friends, but if they went outside of parameters, how can you blame the system? If they aren't able to keep track of their average depth correctly (which you admitted they didn't), if they cannot perform a proper ascent correctly (which you admitted they didn't), if they miscalculated their decompression obligation (which you admitted they did), I'm still not clear on how their mistakes are the fault of a system that they were clearly using outside of the parameters of the design. If they can't do it correctly, they shouldn't be using it. That goes for ANY decompression strategy, whether it's ratio deco, a MultiDeco plan, a VPM-B deco schedule, or one of the VVal-18 tables from the USN Rev. 7 manual.

Let's be clear so I fully understand. If you exceed the speed limit, and you get pulled over, do you get the ticket, or does the car manufacturer? Same same.

How many cases of people getting DCS are there every year? I don't know (you'd have access to better information than I do, I'm honestly curious), but I bet most of them aren't getting bent by screwing up ratio deco. How many ratio deco-planned dives are made every year that result in DCS, I'm willing to bet the number is pretty darn small. Ask AJ, I'm sure he'd know since he's much more in that realm than I am. But considering the level to which AJ (and guys like him) have quite successfully used the system pretty much proves that the fault lies elsewhere.

I didn't know there were two... the problem doesn't lie in the algorithm. It lies in the diver trying to keep up with that while dealing with narcoses and other distractions. It's also an oversimplified approach to decompression.

Here's the problem though, as designed, being narked isn't an issue. If you can't do simple math at 75% of your max depth breathing mix with an shallow END, you've got other problems to begin with.

Just like the other thread where that Stuart guy was talking about doing a gas switch while upside down on an ascent like while crazy positive in a current with mermaids and other stuff. Guess what, you don't do the gas switch until you've got your sh*t sorted. You don't try and create a deco plan with you're distracted by a bunch of stuff. And considering the framework that the system was designed for, you SHOULDN'T be distracted because your ONLY job is figuring out the teams deco plan. You're not shooting an SMB, you're not trying to switch gas at the same time, you're ONLY running the deco plan. So again, problems arise when people try and fit their diving into the framework, instead of the other way around.

As far as being oversimplified, I don't know that that's actually the case. It seems to work pretty well when used correctly. But again, if used incorrectly, it can bend someone as easily as anything else.

 

[The Chairman]

Look carefully at what I wrote. If they are incapable of using the system as designed, it's not the fault of the system.

Once you descend past 80 feet, most everyone is incapable of using the system "as designed". People rail about the possibility of a PDC failure, yet the human brain fails all the time and consistently so with depth. Denial is not a good strategy in dealing with this. In short, the system can't be reliably used by the average diver. Ergo, the system fails regularly in it's execution. It's too much for the narced mind to deal with and keep up with all the other tasks.

You can contend that a bomb is safe as long as you can run fast enough when you set it off. But when people are regularly injured while trying to follow those instructions what do you do? Blame the people or stop using that bomb? Too many people are being injured with RD for me to ever feel comfortable with it's use. Playing Russian Roulette is not my idea of fun.

 

[PfcAJ]

Pete, do you have any formal training on ratio deco?

You're just mistaken on so many things about it, including how to use it in the water.

 

[boulderjohn]

If they are incapable of using the system as designed, it's not the fault of the system.

You are missing the fact that the human brain and their ability to do these computations is very much a part of the system, just as the processing unit in a computer is part of the system.

 

[Bennno]

Once you descend past 80 feet, most everyone is incapable of using the system "as designed". People rail about the possibility of a PDC failure, yet the human brain fails all the time and consistently so with depth. Denial is not a good strategy in dealing with this. In short, the system can't be reliably used by the average diver. Ergo, the system fails regularly in it's execution. It's too much for the narced mind to deal with and keep up with all the other tasks.

You can't think straight below 80' feet?

Lots of people do dives they shouldn't be doing... not everybody that managed go get a Trimix card is a competent diver. Have you considered that?