Are dive computers making bad divers?

[stuartv]

According to Baker's paper's the pressures are converted to fsw (or msw) before being used in the calculations. The type of water entered is used to modify the calculations. If this is the case your computer will not calculate the correct NDL/deco for diving in the Dead sea which has a much higher density than typical ocean water.

I believe that is incorrect.

See RonR's (from Atomic) post here:

http://www.scubaboard.com/forums/co...25-petrel-2-salinity-setting.html#post7516590

 

[Storker]

DC's can't measure depth directly. They measure pressure and given the type of water (fresh or salt) can calculate depth which is then displayed on your computer. Physiologically, inert gas loadings depend on pressure but this raises an issue: what does the algorithm actually use? According to Baker's paper's the pressures are converted to fsw (or msw) before being used in the calculations. The type of water entered is used to modify the calculations. If this is the case your computer will not calculate the correct NDL/deco for diving in the Dead sea which has a much higher density than typical ocean water. If the calculations are done in pressure units then it doesn't matter what the medium is.

I'm not with you.

Let's say my computer believes I dive in salt water (1.025 kg/dm³), but I dive in freshwater (1 kg/dm³). At 30m physical depth, my pressure is 1.013 + 3*1.0 bar = 4.013 bar, which is what my computer thinks is 29.3m. If my computer knows I'm diving in freshwater it'll understand that I'm at 30m and tell me so. However, my on- and offgassing depends on pressure. No matter what my computer thinks (and tells me) is my physical depth, it should use 4.013 bar as my effective pressure. Not that it matters much, though, a 2-3% error in depth estimation means roughly nada WRT bubble formation and DCS, particularly on a rec dive.

You can take this into the extreme: Let's assume I dive in a medium with a density of 2 kg/dm³. My pressure at 15m would be 4 bar, just as it would be at 30m in freshwater. Does it matter that my computer thinks I'm diving in freshwater and tells me I'm at 30m? I sincerely hope not, because the meters are irrelevant, it's the bars that determine my on- and offgassing.

Bottom line: fsw/msw isn't a physical depth. It's a pressure.

 

[FinnMom]

Why would you equate not knowing/remembering how to use tables with being a bad diver? If you never find practical need for a skill (Algebra, High school French or diagramming sentences are examples for many people) you will forget most of it in a few years, certainly in tens years or so. Almost everyone learns how to use tables, and many, many of them never find a need for the skill after the last time they did it in class. This might be an indication of middle-aged memory skills, but it doesn't make them bad divers. It is definetely an indication of how useful the skill is for the average diver -and there is nothing inherently wrong with that.

Computers are much easier and flexible, don't have to be laminated to stay dry, understand perfectly well Nx % like 27 or 31, often give you a longer bottom time and many save fun & useful data like water temp, average depth, etc. You need a depth gauge and timer anyway, and you often can't find these items much cheaper than in a computer. It's also true that many boats require all recreational divers to have computers nowadays.

Frankly I've never understood the fuss: I thought use of the tables was fairly obvious even w/o instruction and I'm sure most reasonably intelligent persons can re-learn or the learn the skill if they ever have the need. Obviously a trimix student training for a 100m dive needs a completely different skill set and level of competence, but the average diver is a world away from people who can knowledgeably discuss decompression models, M-values etc.

 

[bergersau]

I wonder if that particular issue is down to whether it was reading the right "type of water" ie was it set for the wrong type (ie fresh water when it should have been seawater or vice versa). This would possibly explain it reading the wrong depth for the pressure due to the density difference.

AFAIK all computers will base the loadings on the pressure so will always give the correct NDL/Deco.

No, That model computer does not allow for setting the salinity.
I soaked the unit in luke warm fresh water and replaced the battery. The next dive the computer reset to surface mode 1 minute into the dive.
I've replaced the computer, the mosquito was 13 years old (though under 100 dives) when it failed.

 

[NAM001]

I don't think your point is the issue. I learned pn junction theory in electronics. I have never knowingly used it again cause when I learned it, I proved the basics in school, which then turned in to givens so to speek. In algebra you don't think about the communitive or distributive theory's. You just know they work because of prior proof's you did when you learned in school. In speaking you diagrammed sentences till you understood the relationship of sentence structure and you don't use them again. You say bob and I went to the store. because broken down it is bob went to the store and I went to the store,,,, the and combines two thoughts into one joint thought. and you don't say "me a a bob went to the store". because..... bob went to the store is good but me went to the store is just plain use of words. Yet how many talk like that ? This is what diving with a computer is when you don't learn the basics of tables. The tables are the foundation. If you cant recognize a bad result the computer is no longer a tool it is your enemy. I really don't have any idea how a diver, as ignorant as so many are, renting a computer knows when it was last used. You have to just take the word of the shop it was reset from this mornings rental or has not been used for the last 24-28 hours. Most do not even know to ask the question. That is one reason i have always owned my own. As long as everything goes right. turning your dive over to a computer is OK I guess.

Why would you equate not knowing/remembering how to use tables with being a bad diver? If you never find practical need for a skill (Algebra, High school French or diagramming sentences are examples for many people) you will forget most of it in a few years, certainly in tens years or so. Almost everyone learns how to use tables, and many, many of them never find a need for the skill after the last time they did it in class. This might be an indication of middle-aged memory skills, but it doesn't make them bad divers. It is definetely an indication of how useful the skill is for the average diver -and there is nothing inherently wrong with that.

Computers are much easier and flexible, don't have to be laminated to stay dry, understand perfectly well Nx % like 27 or 31, often give you a longer bottom time and many save fun & useful data like water temp, average depth, etc. You need a depth gauge and timer anyway, and you often can't find these items much cheaper than in a computer. It's also true that many boats require all recreational divers to have computers nowadays.

Frankly I've never understood the fuss: I thought use of the tables was fairly obvious even w/o instruction and I'm sure most reasonably intelligent persons can re-learn or the learn the skill if they ever have the need. Obviously a trimix student training for a 100m dive needs a completely different skill set and level of competence, but the average diver is a world away from people who can knowledgeably discuss decompression models, M-values etc.

 

[phoenix31tt]

This is what diving with a computer is when you don't learn the basics of tables. The tables are the foundation. If you cant recognize a bad result the computer is no longer a tool it is your enemy.

Why do you keep saying that...

Tables are not the foundation, they don't teach you anything about deco theories... They do just about the same thing that computers do (a little less actually)...

They tell you how long you can stay down on a first dive... And how long you can stay down on a repeat dive after a certain surface interval...

As was mentioned by me and others in this thread that information can be sought from a number of places including a computer, dive simulator, dive planning tool etc.


It's all about in the teaching of decompression theory... you can teach the same theory, table or computer doesn't matter...

I believe when you were thought tables your instructor thought you some level of deco theory along with it so you assume that "teaching tables" = "teaching deco"...

That's just a misconception on your part... he illustrated the theory using tables... which you can easily do with a computer as well



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[stuartv]

Why do you keep saying that...

Uhhh.... because if you learn the tables, you can potentially recognize a bad result from a computer? Without learning any decompression theory?

If you know the tables even modestly well, and you've been diving on air for 40 minutes at 60 feet and your computer says you have 50 more minutes of NDL, you would have a good shot at realizing that something is wrong with your computer. Without knowing ANYTHING about deco theory.

 

[spectrum]

Uhhh.... because if you learn the tables, you can potentially recognize a bad result from a computer? Without learning any decompression theory?

If you know the tables even modestly well, and you've been diving on air for 40 minutes at 60 feet and your computer says you have 50 more minutes of NDL, you would have a good shot at realizing that something is wrong with your computer. Without knowing ANYTHING about deco theory.

How likely is that failure mode? You have established that it is sensing depth and the display is operable, in other words it operating and not detecting an internal fault. After that it's algorithm execution. Are you saying it might make a mistake?

 

[packrat12]

Tables are about useless. They are great for calculating the rare Square Dive profile but that is about it. I did my first 500+ dives on tables. The moment I bought a computer, my tables went into storage. I can honestly say I have had 1 computer failure for my family since 1997. It was due to a pressure sensor hang from flying. Reset before the 1st dive and did not have further problems. Considering the odds of having a computer failure, I would suggest that my watch failures - which were common including a Heuer dive watch, bumping the max depth indicator on the depth gauge, bottom timer failures, forgetting to set the watch etc, I had a lot more failures when doing tables! If my computer has failed, exactly how will I know MY bottom time, MY max depth and maybe MY surface interval????? If I do not know these, how can I determine by table information? These was a common mistake when we used tables.
Maintain your computer. Change batteries before they get low. Change them at the beginning of every season. Replace if any issues are observed. This will reduce computer failures to really just noise.

If I need a backup, e.g. critical dives, I will carry a second computer with me. If not, I will blow a dive if I have a computer failure. I have yet to have to do this though so a second computer for recreational diving would not be cost effective.

Understanding Decompression theory at least to a rudimentary level is much more important. Then you will understand what the computer is doing. You will understand what excursions and settings will really mean to you.

stuartv - Exactly how would you know your times and depths? You have a computer failure... Did you set your watch and recalculate based on tables if this is a repetitive dive? Did you have an alternate depth gauge as your computer is now considered failed? Your dive has probably been multilevel.... Simple table NDL has little correlation to a computer NDL in many dives as they are multilevel. Are you going to pull a table and calculate it on the spot including for the multilevel profile??? I have had dives where my second dive was deco and my third dive 'started' in deco if on tables but on the computer they were all within NDLs - How can I pull a table for these??? For a recreational diver the option is simple, monitor the computer and end the dive if a failure is noted. When I dove tables, I would bring them down with me on every dive to recalculate for deviations. For a recreational dive, I remain in NDL on the computer and in a failure mode - I end the dive. Period. I have yet to need to recalculate using tables because of a failure. In fact, I would just blow the next dive if I had one and was pushing NDLs.

 

[USdiver1]

It is becoming more and more frequent that I find myself with divers who are extremely computer dependent. For those senior divers who have been diving since before the computer revolution, do you feel that the new generation has been idiotized by computers, or no.

I've been certified for nearly 40 years, and I didn't use/purchase a computer until 2012, so the vast majority of my experience is on self calculated tables. Yes, I have noticed a dependency on computers from divers trained in the last 15 - 20 years, especially those joining our sport within the last 10 years. A good area to see this lack of knowledge is in a DM course where what had been very basic table calculations (from my initial training back in the 1970s) was treated as a whole new area of training. IMO, PADI (and possibly other agencies) has been too lax in teaching the tables since the 1980s on, what with their multi-level "wheel", electronic dive planners, etc.

Tables are not hard to learn, and once mastered, provide an additional level of self-confidence to the recreational diver. While I dive with an air integrated computer now, I always have my back up analog depth and pressure gauges, dive watch and a waterproof copy of the Navy tables and repetitive dive tables on my dives. Just like old times.