Wisdom of trusting one's dive computer?

[NAM001]

Who defines "minimum needs for recreational diving"? Even the major training agencies, which have been the subject of criticism (deserved or not) for setting their standards at the bare minimum to keep basic recreational divers safe, appear to have been upping their game in recent years. If I recall some prior discussions correctly, PADI now teaches basic gas planning and has students plan a complete dive on their own. That says to me that dive planning is getting more attention than it did when I took the basic OW class 20 years ago. I was woefully unprepared to plan dives. Many of us suspected that we should be doing a little more than just jumping in and hoping for the best using the information available from our instruments, but few of us did anything to rectify that. I don't know exactly what PADI requires in the basic OW course these days with respect to dive planning, but I am guessing the instructors who take it seriously teach more or less what has been suggested in this thread (aside from the discussion on gradient factors).

IMO OW courses recommend no deeper than 60 ft. So why train beyond teh skills you need for 60 ft? Ritgt or wrong I am viewing this as an admission that after finishing OW they know divers are going beyong the recommended 60 ft depth and are trying to head things off with dive planning, Under the current structure with Ow being what it is i would expect the most appropriate place for planning of any extent would be AOW for dives to 100 ft. Planning is there to define limits and prevent becoming a statistic. would anyone plan a dive in a pool? The only reall dive planning in shallow water is how not to run out of air. that does not need planning. There is no planning to avoid deco in shallow water. If I were a student I sould say that any phase in OW is a waste of time other than laying the basic planning concepts for further traing to build on. Here is what I envision planning to be for an OW outside the training environment. my tank has x gas i use it this fast , i have x minutes at 45 ft of gas. NDL is say for argument 90 min so no deco threat. That is all moot because you should have a SPG or other like device. The most you can realistically plan is what you are going to do and define the buddy pairs.. Though tasking enough for a new OW its really just jumping through hoops with out gain.

 

[Lorenzoid]

@KWS , I don't disagree. In my opinion, the most important aspect of "dive planning" is simply to go through all the issues one by one and determine which are significant for that dive and which, if any, are not. If from your anticipated dive profile you determine that running out of no-deco time is not an issue, great. At least you gave it a couple of seconds of thought before splashing. Making it a habit to hit each point before every dive may not be important at first, but as you point out, divers can be expected to keep advancing their limits as they gain experience, and there is no bright line between a dive for which "it's okay to just splash" and a dive for which "I ought to do some real planning."

 

[NAM001]

Why would you want to do something incorrect like this? I understand its value for air consumption, but it is not correct for nitrogen uptake.

what is wrong with average depth. other than trying to average teh entire dive. if you do a dive to 60 ft and you varry from 62 to 58 you average it to 60 for calculaton purposes. RD is not erven that critical. and again in rec diving you are not concerned per se about N2 intake becasue you do NDL dives.

 

[NAM001]

@KWS , I don't disagree. In my opinion, the most important aspect of "dive planning" is simply to go through all the issues one by one and determine which are significant for that dive and which, if any, are not. If from your anticipated dive profile you determine that running out of no-deco time is not an issue, great. At least you gave it a couple of seconds of thought before splashing. Making it a habit to hit each point before every dive may not be important at first, but as you point out, divers can be expected to keep advancing their limits as they gain experience, and there is no bright line between a dive for which "it's okay to just splash" and a dive for which "I ought to do some real planning."

agree totally. You need to do it to institute the routine of planning. The deeper you go the m ore there is to consider when planning.

 

[tursiops]

in rec diving you are not concerned per se about N2 intake becasue you do NDL dives.

Nonsense. What NDL means is that you have not exceeded an allowable N2 intake. Of course you are concerned about it.

 

[NAM001]

Nonsense. What NDL means is that you have not exceeded an allowable N2 intake. Of course you are concerned about it.

Your concern ends when you get the NDL time. Tech tracks gas onload and off load not rec divers. Thats why REC has tables and computers to do the job for them. If you want to conduct a rec dive like a tech dive that is another story. When a rec diver doea a dive thay look at a table adn it says 20 min at 100 ft and the computer keeps track of the remaining time. No where is there a thought about onload and off load of N2.

Ndl doesn't say you have exceeded intake per se. it says you have exceeded the allowable level to get you to the surface with in your conservative setting. Just becassee your computer says you are in deco it does not mean you are in fact in deco. It means to get to the surface in hte conservative setting youcan not do it at the perscribed ascent rate. It means that if you surface you will arrive with a higher residual N2 level than you planned for. This his the crux of 2 computers on the same diver one in low and the other in high one has a NDL of 12 minutes and the other has a NDL of 20. you are at minute 13 are you or are you not in DECO. NDL reflects a condition to aadhere to in order to yeild a desired result that may or may not be a hazzardous one. GARBAGE IN GARBAGE OUT. There is so much lacking in our training when it comes to topics like this that could be included in the AOW class.

 

[tursiops]

Your concern ends when you get the NDL time. Tech tracks gas onload and off load not rec divers. Thats why REC has tables and computers to do the job for them. If you want to conduct a rec dive like a tech dive that is another story. When a rec diver doea a dive thay look at a table adn it says 20 min at 100 ft and the computer keeps track of the remaining time. No where is there a thought about onload and off load of N2.

Ndl doesn't say you have exceeded intake per se. it says you have exceeded the allowable level to get you to the surface with in your conservative setting. Just becassee your computer says you are in deco it does not mean you are in fact in deco. It means to get to the surface in hte conservative setting youcan not do it at the perscribed ascent rate. It means that if you surface you will arrive with a higher residual N2 level than you planned for. This his the crux of 2 computers on the same diver one in low and the other in high one has a NDL of 12 minutes and the other has a NDL of 20. you are at minute 13 are you or are you not in DECO. NDL reflects a condition to aadhere to in order to yeild a desired result that may or may not be a hazzardous one. GARBAGE IN GARBAGE OUT. There is so much lacking in our training when it comes to topics like this that could be included in the AOW class.

If I am understanding what you are saying, you are not understanding what you are saying.

 

[Stoo]

The GUE has their own way of doing things. Is it the right way of doing it? I don't know, it seems to work for them, but it isn't how I would want to dive.

Same. I hosted a GUE bunch in Tobermory and they wouldn't dive a couple of our best dives because not everyone in the group was trimix certified. These are dives that everyone else coming to town does on air or nitrox without problem.

As for trusting your computer... I also dive Shearwater computers. I figure Bruce and his team know a heck of a lot more about decompression stuff than I ever will. Almost all of my dives are "deco light"... 5 - 15 minutes deco usually on O2, but some are "bigger"... 200' plus on mix with an hour or more of deco. I plan the dives, cut tables and ignore them in my pocket, relying on my two Shearwaters to do the job they were designed to do.

I might add that we rely on all sorts of technology when we dive... our regulators, inflators on our BCDs and suits etc. We don't second guess those things, why would we doubt a solid computer with a a proven record of reliability. (And which can easily be doubled up for redundancy if you REALLY want to be sure.)

 

[AfterDark]

Both my PDCs are for reference or backup/second check. I do not "trust them" or any other piece of consumer grade hi-tech for that matter. I plan my dives with US Navy tables as I have for 50+ years and more than 2080 dives, without a sign of DCS. I've only owned PDCs for >10 years and bought them more to placate charter operators than for my own use. I do find them useful for logging dive data and as a depth gauge to use with my watch. Those are my 2 main tools for monitoring NDL a depth gauge and a watch.

 

[Stoo]

Both my PDCs are for reference or backup/second check. I do not "trust them" or any other piece of consumer grade hi-tech for that matter.

So you don't trust the computers that run your car at 70 mph? Or the ABS system in your brakes. How do you bypass those? Or your regulators? How do you analyze your gas without using technology? Does your fill station test for CO in their air with something other than a digital monitor?

I'm sorry, but your argument makes no sense. Like you, I've been at this for 45 years. logged 5500 dives, and have never been bent on recreational/technical dives... neither in the olden days of USN tables, or DCIEM tables... or, wait for it, using computers. I have been bent in a commercial environment when our profiles were cut using tables.

All I know is that I wasted countless hours of in water time when I ran tables in profiles that weren't square. The computers allow me to maximize my down time in a way that no table ever will.