Skin Bends

[PeterNBiddle]

2) What happens if you battery dies during your dive? Do you cut it short and take your buddy to the surface with you? Maybe you keep going and just hope for the best so you do not look like you don't know what you are doing?

I dive with two computers. Duh.

---------- Post added March 17th, 2015 at 06:24 PM ----------

Id like to see some data as well. If dive tables are truly safer than computers, surely there must be a way to show that. Is there a study showing it?

Or can you show us 10 dive profiles where computers create clearly more dangerous dives than square profiles?

I'm a bit confused by the whole argument, actually. Diving a table is diving an algorithm - it's just a very crude algorithm done on paper and it does nothing to account for diver behavior - it assumes the profile is perfectly square.

But it's just an algo. Diving a comp is just a different implementation of an algorithm.

There's actually no reason I can think of that one is automatically better than another.

Neither knows if you have a PFO, if you are dehydrated, if you flew to recently or if you drank a lot last night.

Square is not better than a comp any more than a slide rule is better than a calculator. Given the same data they should produce the same results.

 

[Tunaman68]

This table argument is such ridiculous semantics and I (being the OP) doubt very much that diving tables with flat bottoms would have changed the outcome in what seems to be just plain bad luck. I feel the same about saying 'if he were diving nitrox, this would not have happened'. Maybe yes, maybe no. We can all be armchair quarterbacks and say if/then, but in reality this incident has really brought home the fact that anything can happen on any dive, even when you follow all the rules.

The information and experience I have gained during all of this will make me a better diver and I can take this knowledge and help myself and hopefully others too.

I will continue to dive my computer and be thankful that my favorite sport has progressed into the 21st century. I will take new precautions and take advantage of nitrox. It took 25 years and 1,500 dives before I had a problem, and I will hope that it will be another 25 before the next one.

Flew back to LAX today with no problems, and will be glad to sleep in my own bed tonight. Thanks everyone for your input.

 

[PeterNBiddle]

This table argument is such ridiculous semantics and I (being the OP) doubt very much that diving tables with flat bottoms would have changed the outcome in what seems to be just plain bad luck. I feel the same about saying 'if he were diving nitrox, this would not have happened'. Maybe yes, maybe no. We can all be armchair quarterbacks and say if/then, but in reality this incident has really brought home the fact that anything can happen on any dive, even when you follow all the rules. The information and experience I have gained during all of this will make me a better diver and I can take this knowledge and help myself and hopefully others too. I will continue to dive my computer and be thankful that my favorite sport has progressed into the 21st century. I will take new precautions and take advantage of nitrox. It took 25 years and 1,500 dives before I had a problem, and I will hope that it will be another 25 before the next one. Flew back to LAX today with no problems, and will be glad to sleep in my own bed tonight. Thanks everyone for your input.

You don't drive a car with a computer in it, do you? Or God forbid fly an airplane with a computer in it?

 

[Freewillow]

You don't drive a car with a computer in it, do you? Or God forbid fly an airplane with a computer in it?

Good joke, I amost fell in the trap. Well done mate

Airbus A320 Primary Flight Controls - DutchOps.com Powered

In contrast with the flight control system installed on conventional aircraft, the Airbus A320 is fitted with a fly-by-wire flight control system. This means that the mechanical linkage between control column and control surface has been replaced by electrical wires. Just like the Boeing 737, the Airbus A320 flight controls are divided into primary and secondary flight controls. Both the primary and secondary flight controls are controlled by a total of 7 computers. The primary flight controls fitted on the aircraft are controlled by sidestick inputs and digital processing by the Elevator Aileron Computer (ELAC), the Spoiler Elevator Computer (SEC) and Flight Augmentation Computer (FAC). When the primary flight controls on the Airbus A320 are being operated, electrical signals from the sidestick or Flight Management and Guidance System (FMGS) are send to the flight control computers before being passed to the flight control hydraulic actuator.

 

[TSandM]

I think it's fairly intuitive that, if tables calculate your nitrogen absorption on the assumption that you spend your entire time at your max depth, and computers calculate it based on the depth where you ARE at any given time, that for any non-square profile, the tables will result in less total nitrogen absorption, since they will send you up earlier than a dive computer will do. And I would be willing to accept that less nitrogen loading results in less DCS risk.

The difficulty with DEMONSTRATING that is that the DCS rate is already so extremely low in recreational diving, that it would take an enormous number of dives done by two groups to show a significant difference in risk. And since, except for technical diving (and slowly, probably even there) tables have essentially been abandoned, you would have a great deal of difficulty collecting those data.

We are probably down to where factors which are almost completely not understood determine the occurrence of most recreational DCS. I remember listening to Michael Powell (Dr. Deco here on SB) talking about the work they did on the PADI RDP. They found that some people bubbled almost all the time, and others didn't bubble no matter WHAT kind of profile they dove. Those individual factors are, as far as I know, a complete mystery, and may account for the non-zero incidence of DCS today.

 

[Freewillow]

Why am I so adamant on this issue? Simply because this could lead, rather unexperienced divers reading here, to believe that they would be better off saving their $$$ for something else than a computor.

I have been through a lot of tables myself but I know one thing. Recreational dives during a vacation are a succession of multi levels dives in succession ( 1 to 2 but can go to a crazy 5!) for several days. It is always possible to do it on tables. I remember the famous circular table from PADI . But the chance for error is very significant for successive dives and if you take all dives as square dives, you will end up with VERY SHORT dives at the end of the day.

To a point that you may ask yourself if you would not ne better off on the beach. Well, that for sure will seriously decrease your chances for a DCS hit .

 

[PeterNBiddle]

I think it's fairly intuitive that, if tables calculate your nitrogen absorption on the assumption that you spend your entire time at your max depth, and computers calculate it based on the depth where you ARE at any given time, that for any non-square profile, the tables will result in less total nitrogen absorption, since they will send you up earlier than a dive computer will do.

Hold on - you're comparing apples to oranges, aren't you? If you aren't diving square then you aren't following the table. If I go to max depth and then go 1 foot deeper I've blown the table, right? But my guess is most table divers would just shrug and not sweat 1 foot for 10 seconds... Why? Because it's no big deal. But as soon as i do that, I'm essentially acting as my own comp running an unknown algo on imperfect data.

To compare safety we have to compare a perfect square dive following the table to the inch and second with a perfect comp dive. Otherwise you have to say that any non-square table dive might include going past max depth or too slow of an ascent, at which point we can try to figure things out, but it's hard. If you deviate from the square you can also stay down too long.

With a comp, it is right there with you. I posit that a perfect square dive is just as safe as a comp dive when both the tables and comp are set to the same variables. An imperfect square dive can be safer or more dangerous than a comp dive set to the same variables, depending on the imperfection.

 

[TSandM]

Well, if you follow the rules for the tables, if you exceed the depth by one foot, you move to the next category. If you don't follow the rules for the tables, you aren't diving tables, and you can't say anything about the comparison of people breaking rules on tables with people following computers.

It stands to reason that if I do a dive where I swim downslope to about 90 feet, and then swim upslope to my entry point, I have spent the vast majority of the dive at a depth shallower than 90 feet. But the tables will consider that all of my bottom time was spent at 90, so my total dive time will have to be pretty short - about 30 minutes, if I was diving air. Diving a computer, though, I could probably do an hour's dive that the computer was entirely happy with. Since the computer thought an hour was fine, and the tables made me end my dive at 30 minutes, doesn't it seem clear that the tables are more conservative, and the DCS risk ought to be lower?

 

[Rich Keller]

Why am I so adamant on this issue? Simply because this could lead, rather unexperienced divers reading here, to believe that they would be better off saving their $$$ for something else than a computor.

Ah I see now, it is about their $$$ not their safety! So the computer is better because it costs more? Or you make more selling them? So you want to give the impression that diving a square profile is bad so they will need to buy a computer. The only real problem you have with a square profile is that it only requires a watch & depth gauge.

 

[Freewillow]

Ah I see now, it is about their $$$ not their safety! So the computer is better because it costs more? Or you make more selling them? So you want to give the impression that diving a square profile is bad so they will need to buy a computer. The only real problem you have with a square profile is that it only requires a watch & depth gauge.

I don't understand...................and I do not care. .