learn from tables or dive computer?

[BIGSAGE136]

I apologize for any hurt feelings. I just cant imagine how people dived before the computer. I guess they are all dead.

 

[halocline]

Wow, this thread has gotten a little heated! Anyhow, two things stand out to me about some of the arguments:

1. Many people post about "when your computer fails..." okay, how about a real life experience of a dive in which the computer failed and the dive was finished on table, including your exact procedure for doing so. No "what ifs", let's hear from experience. I have an idea how I would handle a dive if my computer failed, depending on how it all happened, but I'd like to know how many of the people that are so concerned with the possibility of computer failure have experienced it.

2. Those who are arguing against the value of ascent rate indicators in buoyancy training, saying "that should happen in initial training" are not seeing this from the student's point of view. Regardless of initial training, when students venture into the ocean for the first time and are in blue water with no reference for depth, it will be MUCH easier for them to control their buoyancy if they have a sensitive ascent rate indicator. This could just as well be on a bottom timer as on a computer, but the point is, when you can look at an instrument that tells you precisely when you're going up and how fast, you're going to learn quicker and better how to control your depth. What could possibly be wrong with that? This is especially true because I would be willing to bet that the vast majority of DCS cases in single tank rec diving, particularly among new divers, are due to factors like rapid ascents, poor buoyancy control, maybe some dehydration and ancillary factors like obesity, exercise, etc... and NOT by blowing NDL. The simple fact that among most new divers air consumption is pretty high and the capacity of an AL80 (by far the most common size tank) makes it less likely that new divers will exceed NDls by a large margin.

I'm not arguing against the knowledge of tables and their use in dive planning or as a contingency. But, where does it say that computer use means you have to be ignorant of dive tables, DCS causes, etc? I'm in agreement that the original post describing the OW course has a vibe that smacks of "easier, less responsibility" and many experienced divers find that offensive. But computers can be a valuable tool for new divers, along with learning dive tables.

 

[Trainwreck]

We seem to have gotten out of context. I believe that the original thread started with someone saying that his course taught NO TABLES, just computer. I haven't, and no one else I have read has ever said computers were bad. WE SAID teaching ONLY computers was bad. Computers are certainly a valuable tool. I use mine extensively but not to the exclusion of the tables when teaching.

 

[MikeFerrara]

Wow, this thread has gotten a little heated! Anyhow, two things stand out to me about some of the arguments:

1. Many people post about "when your computer fails..." okay, how about a real life experience of a dive in which the computer failed and the dive was finished on table, including your exact procedure for doing so. No "what ifs", let's hear from experience. I have an idea how I would handle a dive if my computer failed, depending on how it all happened, but I'd like to know how many of the people that are so concerned with the possibility of computer failure have experienced it.

I've been around a few computer failures. The first catagory were when they failed out of the water. These were winter dives, some of them ice dives) and the computers just didn't work. The dives were just done on tables or with a barrowed computer.

We've had several computer failures in the water. My wife just had a computer die during descent on what was planned as a staged decompression dive. No biggie, since we had planned the dive with decompression software and weren't relying on the computer in the first place. She pulled an analog depth guage out of her pocket and we just kep on going.

On several occassions (the same computer) went into surface mode while I was at depth. Fortunately those dives were in a 25 ft deep quarry where I didn't need a computer, table or depth guages. You just can't get deeper in that place without a shovel.

We have had computers read depth wrong. I've seen them off more than 10 ft. We noticed it because we knew the site and the depths. I don't know how often it has happened when we didn't notice. Again, in those instances we weren't relying on the computer for decompression information.

Note that all the failures that I've mentioned other than those that involve a computer that just dies or never comes on, were all intermittent...not working right one minute or on one dive and fine on the next.

I suppose that most of these failures could also happen with an electronic bottom timmer. The only difference is that when we use a bottom timmer we aren't ever relying on it to calculate decompression.

2. Those who are arguing against the value of ascent rate indicators in buoyancy training, saying "that should happen in initial training" are not seeing this from the student's point of view. Regardless of initial training, when students venture into the ocean for the first time and are in blue water with no reference for depth, it will be MUCH easier for them to control their buoyancy if they have a sensitive ascent rate indicator. This could just as well be on a bottom timer as on a computer, but the point is, when you can look at an instrument that tells you precisely when you're going up and how fast, you're going to learn quicker and better how to control your depth.

A depth guage works just fine for an ascent rate indicator.

What could possibly be wrong with that? This is especially true because I would be willing to bet that the vast majority of DCS cases in single tank rec diving, particularly among new divers, are due to factors like rapid ascents, poor buoyancy control, maybe some dehydration and ancillary factors like obesity, exercise, etc... and NOT by blowing NDL. The simple fact that among most new divers air consumption is pretty high and the capacity of an AL80 (by far the most common size tank) makes it less likely that new divers will exceed NDls by a large margin.

Yes, there are lots of rapid ascents in recreational diving. In my observation they are due to poor skills and not knowing how to ascend, poor buoyancy control and lack of ability to manage problems midwater which lead to unintentional ascents. ok, maybe some divers just ascend too fast but some if not most of those divers need more than a beeper. They need some schooling into how to ascend and how to judge ascent rate.

 

[Swan1172]

My take on the whole matter is that you need to first you learn to dive using tables and then you learn to dive using computers. I think it is important to learn tables if for no other reason than it gives you a better perspective on how a dive computer actually works. I also see dive tables as providing a certain amount of redundancy in dive planning.

 

[Blackwood]

tables... gives you a better perspective on how a dive computer actually works.

Not sure I can agree with that.

 

[halocline]

Mike, those are the sort of experiences I'm looking for, thanks. In each case you described, using tables to finish a dive started with a computer did not happen; the one deco dive you described was planned and executed with planning software, not the computer. The others were shallow enough so that you had no decompression concerns. Right?

 

[Blackwood]

Mike, those are the sort of experiences I'm looking for, thanks. In each case you described, using tables to finish a dive started with a computer did not happen; the one deco dive you described was planned and executed with planning software, not the computer. The others were shallow enough so that you had no decompression concerns. Right?

That's what it seems like.

Using tables to continue after a computer failure is do-able so long as you know what's going on.

I won't use the term "turn off their brain," but many people when using computers don't keep a running log (mental or written) of what they've been diving. If your computer craps out after a couple of dives and you don't have any idea what your profiles were, you can't just look at a table and continue. Many of the recreational computer divers I've encountered simply don't have the situational awareness to use tables to continue after computer failure.

 

[halocline]

That's what it seems like.

Using tables to continue after a computer failure is do-able so long as you know what's going on.

Right, I was thinking about this. You'd have to:
1. Have a back up timer and depth guage, with a max depth indicator
2. Have table with you
3. Have knowledge of prior dive BT/depth and SI, and ability to figure pressure group for current dive.
4. Hope that you weren't already past NDL limits on the table

I don't usually dive with a back up depth guage, but if were diving solo I'd sure have one. I also don't take tables with me on a dive; they're in my reg bag on the boat. So if I were caught with a computer failure mid-dive, I'd have to be pretty cautious about continuing. Since I'm usually pretty aware of my profile, if I was in a familiar situation, like a shallow reef in Cozumel, I'd continue the dive at a depth of 30 ft or so and do a long 10ft stop. If I were on a wall though, let's say down 60-70 ft, I'd head for the surface.

 

[Matthew]

1. Many people post about "when your computer fails..." okay, how about a real life experience of a dive in which the computer failed and the dive was finished on table, including your exact procedure for doing so. No "what ifs", let's hear from experience.

Good question, I wonder about that myself because I hear it said very often.

My computer once died in the middle of a night dive (because I stupidly ignored the low battery warning) luckily it was a very familiar site and the conditions were ideal. I was leading 5 other divers and I was able to finish the dive, closely approximating our usual profile for that site. Nobody even noticed and none of the other computers even came close to their limits. In other situations, I may simply abort and ascend and do my stop using my buddy's gauge.

What I'm trying to say is that I was able to continue the above dive because of my familiarity with the terrain and my usual profile, such that even my SPG reading helps me determine where I am in my profile. But I dont see what information a table can provide that will help in that situation. IMO a computer should be backed up by depth gauge and watch or a bottom timer (or another computer), but not by a table.