Dive Computers & O/W

[scubabunny]

hmmm...thought these were called "watches". If a person can't time themselves using a watch, then that person has no business being underwater. (Not to mention watches are ALOT cheaper than computers!)

Seriously, I see your point O2, but I think you have to understand the "concept" first, before you should move into using a computer. Its like math class...you had to learn to do long division using your own brain power first, before you were allowed to use a calculator, right? (That IS still the rule, right? Or am I really showing my age??)

I agree that students should be shown the benefits of computers, and what they are telling you. But I don't think it should be during open water. It is the easy way out.

 

[Iguana Don]

Scubabunny,

Now you've gone and done it, busted my bubble. Please tell me you don't remember Howdy Doody?

:devilish:

 

[turnerjd]

Originally posted by don
Mario,
I am not discounting the use of computers in O/W diving. I am advocating not using them until you have mastered the tables.
We all agree that computers in diving are the future. But you need to know the basics of diving before using one. How do you know if it's working or not.

<snip>
How does an individual make an informed decision as to which computer to use if they can't use the tables to compare it to.

At the stages in their diving careers they are buying computers, they can't even make an informed decision. They have no idea of the different tables that the computer is based on. Sure you can go on recomendations, but you and I know that isn't always the way to go. I am learning still.

<snip>
IMHO I think it would be better if O/W divers waited until they have made 30-40 dives on tables before purchasing a computer.

Personally I don't think wearing an extra computer is the answer, but then again you & I don't always see eye to eye on every topic.

Brothers usually don't

Don

Another vote for spell check

I suspect that you are both approaching the diver safety point of view from opposite ends.

Mario thinks that diving with a computer will stop inexperienced divers doing stupid things - especially the aladin computers which moke SO much noise under water it is unbelievable.

Don is approachin it from the opposite poinbt of view, Divers ARE safer with computers, if they know how to use them properly, and what they are based on, untill that point they are LESS safe, simply because they are sheep following what the computer sais.

I've thought about this for a while, and some time ago, the dive club I was a member of introduced a simple 2 hour course on computers, which was done free, there was a whole load of extra info, different algorithms, different time till fly calculation methods, but also about other more practical computer features. This was made compulsory for all dives done using a computer, and the only requirement for going on it was 20 table dives.

Almost every one that did it appreciated the extra information, bacause if they did it before they bought their computer, they went into the shop armed with a much better idea of what diving they did, what features they wanted and what level of conservatism they wanted. We also had people that had not used a table after their o/w course do it, and they too were amased at what they DIDN'T know about computers.

Obviously in a club situation this works, however, I suspect that a course that is mandatory for computer use out there in the comerial world would not work. In many ways it would be nice to see some-one put thik kind of material into a more advanced course. - one of the other posters (scubabunny) relied that they introduced students to computers on the AOW course. I think that mebe doing one dive of the AOW as a computer dive, and the knowledge development section and review could then nicely cover this extra theory.

Any thought on that?

Jon T

PS for the business side of things there is obviously the perfect oportunity for the instructor to take the students into the shop and play aruond with all the different computers AFTER explaining the extra theory.

 

[o2diver]

The tables are a great tool for planning your dives. I have and do use the tables. I feel though that the computer is a lot safer to use as it takes into account all the variables when giving you your NDL's. It will also help the new diver get use to NDL's based on depth because it is shown on the computer screen. I have a computer but also use bail out tables just incase of a computer crash at depth. Would this be a better way to teach the students since they would have the bennifit of both systems?
Just an idea
o2diver

 

[turnerjd]

Originally posted by o2diver
The tables are a great tool for planning your dives. I have and do use the tables. I feel though that the computer is a lot safer to use as it takes into account all the variables when giving you your NDL's. It will also help the new diver get use to NDL's based on depth because it is shown on the computer screen. I have a computer but also use bail out tables just incase of a computer crash at depth. Would this be a better way to teach the students since they would have the bennifit of both systems?
Just an idea
o2diver

Unfortunately, the vast majority of people have no idea about how to use these extra variables.

The easiest way to visualise how the majority of computers work is to take your tables, and plot a graph of Time (NDL) vs depth (best if you have Depth along the x, and time on the y axis). everything below that line is the safe zone, and everything else is mandatory decompression.

When the computer takes into account all the different variables what it is actually doing is changeing the position of this safe line.

Now, if you immagine a square profile table dive (right up to the NDL) what you do on the diagram is draw a nice line from the max depth, upto the curve, and then across to give you you NDL time in mins. Now, there is at this point a fair ammount of the safe zone outside this dive (the area between the lines just drawn, and the safe curve).

So, now with our multi level dive we do the deep part first, with a NDL, BUT, we have a safe part above this, but below the NDL-line, so we can now put in the second shallower level, and get our time available at the next level up, using up a large area of the safe area.

Computers on the other hand don't work quite like this, they re-calculate every 20 seconds or so. Now, immagine on our diagram that (provided our profile is the correct one, deep first, and gradually ascending), what it is doing is calculating the NDL all the time, so, we end up with thousands of little square profile dives drawn under the curve. Obviously the safe area is now almost infinitessimally small (a good analogy would be calculus, and the idea of delta x).

So, whilst the computer does take into account all these other variables, the changes in the position of the NDL line, are very small in comparison the the large areas pf 'safe zone' available from the square profile table dive, or even the multilevel dive (as you would do with the PADI wheel for example).

No matter what any-one sais, for non-decompression dives, there is a greater margin of safety on the tables, simply because you do not get the benefit of the extra 'safe zone' that is obtainable from multi-level, or computer diving.

Now, the question of wether in application they are safer is a different topic, that is more down to dive discipline, did you plan your dive, and dive your plan.

I couldn't work out a way of putting diagrams in the answer, so if you are interested I can let you have copies of the diagrams I am talking about (I have them in powerpoint, and can save as jpg etc..) mail me, and I can send them to you.

Hope this helps.

Jon T

 

[gozumutti]

So this is already costing me 0.04

My instructor is all for computers, feels we should all get one, but thinks we should be comfortable using the tables first. I agree.

If the computer tells me something, I want to know WHY it is telling me that, and only a working knowledge of the theory can help me there.

gozu

 

[Walter]

.........back in the mid 80's. Of course by then, I had large portions of the tables memorized. They are great tools, but a good working knowledge of the tables is an excellent workbench on which to use that particular tool. I'm very much in favor of holding back on getting a computer until you have quite a bit of experience with tables. My brother just got a computer, but then he's logging in 3 digits now.

There is a misconception about multilevel diving and dive tables. Multilevel diving was invented using dive tables. I was making multilevel dives before my first computer and long before the wheel was developed. Just because you haven't learned the technique doesn't mean it can't be done.

Walter

 

[o2diver]

With all the work that is being done on the algorithims in computers to make them safer, why would we want to use tables that are based on the US Navy tables from the 19???
I would have thought that we would be promoting the use of the latest information and tech. to ensure that we played safe.
????

 

[VegasDiver]

IMHO - Tables should be learned first. It is a good and safe practice. Do I own a computer - yes. Do I trust it explicitly, no. Here it is again, plan your dive and dive your plan. While computers give a diver constantly adjusted NDL's the "get bent" safety factor appears diminished.
I use an air intergrated computer (Oceanic Datamax Pro Plus) which constantly shows "therotical" nitrogen tissue loading and remaining no deco time / remaining gas time. The problem between the tables and computer is that by strictly diving on the computer it would be easy for a diver to "push the limits"
For instance Making a 60 foot dive for 25 minutes (using SSI tables) with a surface interval of 1 hour 30 minutes yealds a repetive goup "pressure group" of "D"
a repetive dive to 60 feet for 25 minutes (SSI tables, 24 minutes residual nitrogen time + 25 minutes of dive time) puts the diver at total bottom time of 49 minutes - the 60 foot NDL (SSI) is 50 minutes.
I did dive this profile on Monday. While I knew on paper that I was at "the limit". However as I did not enter the water from a boat and decend "immediately" to 60 feet (I swam out from shoer w/buddy - 12 minutes to depth) my computer had been happily re-computing my NDL's and nitrogen loading. Once we surfaced a check of my computer revealed that I could make yet another dive on this profile to 60 Feet after a 1 hour surface interval. This profile if done by the tables (SSI) would allow me only 6 minutes at 60 feet before going Bend-O-Matic.
By the way The SSI tables were updated in 1999 and are imprinted with (Doppler No-Decompression Limits Based on U.S. Navy Dive Tables.
How do these add up - see the NDL sample,
SSI Computer Navy
Depth 40 130 260 no data
50 70 80 100
60 50 57 60
70 40 40 50

Just my .02

VegasDiver

 

[Bob]

Have read the the discussions on the use of dive computers during basic certification. I am AMAZED that some instructors promote the use of computers during the certification process. I am PADI AOW and my instructor never mentioned a dive computer during basic instruction that I can remember. He did however see to it that every student in his class was proficient in the use of the dive tables. I am Nitrox certified now and I use a computer, but every dive I set my watch and time my dive just as if I don't have a computer. After surfacing I check my computer against the tables just to make sure there hasn't been a computer malfunction. This just makes me wonder what kind of instruction many new divers are receiving. Makes me wonder just how competent the level of training actually is if all we're worried about is selling a dive computer to a student! Scuba Bob