What to do when you no longer trust your computer ....

[Rick Inman]

I dive four computers at the same time, and follow the one that lets me stay down the longest and come up the fastest.

I'm kidding, of course. But if on a dive your primary computer failed you, just as it was reading, say, 10 mins NDL, and you switched to your backup, and it said, say, 13 mins NDL, what would you do? Go with the new, longer time? Unless they were the exact same computer, they are going to have different NDLs. What if you had, say, 3 mins of NDL when your computer shut down, and your backup had you in deco? Do the deco that you would not have done it your computer hadn't failed? Skip the deco? The point is, if your computer fails, you'll be forced to start using your brain - to at least choose which computer to follow. But what information will your decisions be based on? Best guess? A feeling? The most conservative? The most liberal?

"Hal, open the pod bay doors."

 

[WarmWaterDiver]

Really?! Probly should have sent them back to Oceanic for their excellent customer services. My nearly 4 year old Date Plus does just fine with its once a year battery changes - still have the old ones as spares, still with good charges on a tester.



???? I'm missing something here? That's not much bulks or money, and there's a lot to be said for comfort level.

Maybe I'll feel different with 500+ dives, but I like carrying a lot of back-up safety equipment as I continue to experience new challenges. And I have had and/or seen failures with computers, etc.

I guess we did something we considered far more sensible DD - passed the Oceanic Data Plus units along to someone who could make good use of them - beginning divers living in St. Croix we can visit for housing there. And as I had previously posted, the Bikini operation and Pelagic brand dive computers don't mix - in fact most folks would agree that repetitive deco diving and use of the Haldanean algorithm employed in these units don't mix. Maybe there's something you can discuss with your tech classes instructor if & when you take those classes (or now if you're already taking them).

So, there was and still is no sense to send them to Oceanic in our minds - however the relative battery consumption rate is higher than the Buhlmann based dive computers that are recommended for use at Bikini. In my judgement, the fact that the Oceanglo lighting is activated every time the button is pushed underwater, even in broad daylight, to see the alternate screen display likely has more to do with this - just my semi-technical evaluation. I have enough dives on the original single CR2032 in my TUSA IQ-700 (near 50) with no indications of low battery on that unit that would usually cause a low battery symbol display on the Oceanic Data Plus which uses 2 CR2032 batteries.

Can you post a link to statistics on what most divers do with their dive computers DD? I'd like to see the data firsthand.

 

[WarmWaterDiver]

I dive four computers at the same time, and follow the one that lets me stay down the longest and come up the fastest.

I'm kidding, of course. But if on a dive your primary computer failed you, just as it was reading, say, 10 mins NDL, and you switched to your backup, and it said, say, 13 mins NDL, what would you do? Go with the new, longer time? Unless they were the exact same computer, they are going to have different NDLs. What if you had, say, 3 mins of NDL when your computer shut down, and your backup had you in deco? Do the deco that you would not have done it your computer hadn't failed? Skip the deco? The point is, if your computer fails, you'll be forced to start using your brain - to at least choose which computer to follow. But what information will your decisions be based on? Best guess? A feeling? The most conservative? The most liberal?

"Hal, open the pod bay doors."

well, one way of using one's brain before arriving in this situation would be to

1. Use 2 computers with similar or preferably the same algorithm (back to the 2 watches running at 2 different speeds otherwise).

2. Follow the most conservative of the two as your primary, use the less conservative as your secondary.

No forcing at all on using the brain - completely voluntary and done above the surface. In my case the TUSA IQ-700 is primary and the DR NiTek3 is secondary.

And the way I most remember Hal is, "I'm losing my mind Dave . . . I can feel it". I've known plenty of folks not to own up as well as Hal did when this was happeining.

 

[Charlie99]

But if on a dive your primary computer failed you, just as it was reading, say, 10 mins NDL, and you switched to your backup, and it said, say, 13 mins NDL, what would you do? Go with the new, longer time? Unless they were the exact same computer, they are going to have different NDLs. What if you had, say, 3 mins of NDL when your computer shut down, and your backup had you in deco? Do the deco that you would not have done it your computer hadn't failed? Skip the deco? The point is, if your computer fails, you'll be forced to start using your brain - to at least choose which computer to follow. But what information will your decisions be based on? Best guess? A feeling? The most conservative? The most liberal?

Ummmm, Rick, the computer doesn't force you to dive to the limits, nor does it set your profile. Except for a very deep dive, either 10 minute or 13 minutes of NDL is basically just telling me "very heavily loaded", and my response would be the same.

There is a lot of room for intelligent use of computers between the two extremes of "got to turn of the deco calcs and dumb it down to a bottom timer" and "I just do what the computer tells me".

 

[Rick Inman]

Ummmm, Rick, the computer doesn't force you to dive to the limits, nor does it set your profile.

It doesn't for you, Charlie. But I would submit that for most recreational divers, it does.

 

[Darnold9999]

Rick:

I am curious what you base the comment "that most recreations divers use their computer to set profile and limits". So far I have not seen that behaviour with anyone I have been diving with. A very limited sample, but so far not one dive since I started using a computer has been defined by the computer - and I am pretty flexable in diving any profile that my buddies want as long as I view it to be safe. Have not yet had to veto a dive because it approached computer limits or any other limits. I find most people dive pretty conservativly and use the computer as a safety device that they look at at the end of the dive to see if the dive went according to plan, rather than diving to the limits of the computer. I personally use it as a depth guage and watch until I get out of the water.

The only time I consider I even came close to "diving the computer" was on a liveaboard and we went deeper than we initially planned on a dive and found that we were getting close to the no deco limits so headed up sooner than we really wanted to. But I view this as a good thing, without the computer we would not have wanted to even contemplate changing the plan on the fly.

Re what to do if your computer fails - dive your buddies computer. If that fails - time to call the dive. You should know your depth pretty much all the time, and know where you are re deco. The only issue is your safety stop and figuring out when to stop and do it as you surface. If the vis is less than 15 feet you are going to have a problem, but otherwise look up, when you get within 15 feet of the surface stop - count off 180 seconds and then surface.

If you are in a situation where you can't do this safely - vis is very limited or you are in deco and need multiple stops, call the dive as soon as your computer fails and surface on your buddies.

You can't take a backup of everything, if you do your buddy has one of everything too so now you are taking four of everything "just in case". You become a walking dive shop. Starts to be silly IMHO. I don't take two of anything except I take a backup light at night because lights have a high failure rate, and an octo because others expect it now(a good thing) - no other backups. (I do have two fins, but I don't consider one a backup to the other ) If something essential fails you call the dive - no big deal.

Wrecks and caves etc. would cause me to rethink this, but for purely rec diving I don't think so.

 

[bradshsi]

Rick:

I am curious what you base the comment "that most recreations divers use their computer to set profile and limits". So far I have not seen that behaviour with anyone I have been diving with. A very limited sample, but so far not one dive since I started using a computer has been defined by the computer

www.scubaboard.com/showthread.php?t=124299

In this thread at least, the evidence suggests that the diver in question did exactly that. I'm not aware of any study that gives the absolute % of divers exhibiting this behaviour, so we're left with anecdotes which may or may not be representative of average diver behaviour.

1. Use 2 computers with similar or preferably the same algorithm (back to the 2 watches running at 2 different speeds otherwise).

2. Follow the most conservative of the two as your primary, use the less conservative as your secondary.

With all due respect, you didn't answer Rick's question which was what do you do if your most conservative computer fails ? To me the answer would be to call the dive since your plan would require following the most conservative computer. In which case, having 2 computers isn't really helpful since it doesn't improve your overall system reliability.

Another point is that just because the 2 computers have the same algorithm, does not mean they will agree particularly well. A lot depends on how the computer extrapolates (and how often).

Re what to do if your computer fails - dive your buddies computer. If that fails - time to call the dive.

This goes against PADI's recomendations regarding computer use. Quoting from my copy of their OW manual:

"You and your buddy should not attempt to share a single computer....If your computer malfunctions while diving, ascend immediately according to the instructions of the computer manufacturer....Always back up your computer by calculating with tables".

I would submit that this is quite sensible advice. Say for example your computer failed with 10 minutes of NDL remaining. But your buddies computer showed 25 minutes. It would seem very foolish to share a computer in that situation.

 

[DandyDon]

With all due respect, you didn't answer Rick's question which was what do you do if your most conservative computer fails ? To me the answer would be to call the dive since your plan would require following the most conservative computer. In which case, having 2 computers isn't really helpful since it doesn't improve your overall system reliability.

Another point is that just because the 2 computers have the same algorithm, does not mean they will agree particularly well. A lot depends on how the computer extrapolates (and how often).

Yeah, having 2 different computers with greatly different readings does seem kinda worthless. I dive 2 Oceanic's and the only differences seem to be from one being on my console, one on my wrist - other than on altitude dives, where they may activate with different + 1,000 feet altimeter readings.

On a recent Florida Keys trip, I did 14 dives with 4 Oceanics - testing for downloading capabilities, etc. They essentially read the same, except that I didn't bother setting the Nitrox levels on the 2 in my BC pocket. It was interesting to see the same depths and diving downloaded on Nitrox with one and Air on the other 2. (The oldest one doesn't download.)

Originally Posted by Darnold9999
Re what to do if your computer fails - dive your buddies computer. If that fails - time to call the dive.

This goes against PADI's recomendations regarding computer use. Quoting from my copy of their OW manual:

"You and your buddy should not attempt to share a single computer....If your computer malfunctions while diving, ascend immediately according to the instructions of the computer manufacturer....Always back up your computer by calculating with tables".

I would submit that this is quite sensible advice. Say for example your computer failed with 10 minutes of NDL remaining. But your buddies computer showed 25 minutes. It would seem very foolish to share a computer in that situation.

Yep - very foolish to dive your buddy's.

 

[Jason B]

It doesn't for you, Charlie. But I would submit that for most recreational divers, it does.

So is the problem the computer or the user?

 

[Diver Dennis]

I dive a Suunto Cobra and Mosquito. Last month doing deep wreck dives in Chuuk, the deco times varied my a minute or so but I just do the longest, plus 2 minutes. The only time my buddy Kim, different brand "dove" my computers was during deco, when her deco time was up to 8 minutes less than mine. She stayed for the time on my computers.