Computer Deco Algorithm Freezes

[DeepBound]

This experience underscores the importance of always thinking about what your computer is telling you.

I planned to do three dives this day. The plan for the second dive was to end the dive early if either of us got down to 5 minutes or less of NDL, to make sure we would have time for a good third dive. Near the end of the second dive, my computer still said 20 minutes to NDL, so we turned it based on gas consumption instead, then had a long surface interval before the third dive.

On the third dive, I started paying closer attention to my NDL about half way into the dive. It said 20 minutes until NDL. I checked it again in a few minutes, and it still said 20 minutes. That seemed odd, but I reasoned that possibly we had ascended a bit (we were following a bottom contour and I didn't remember exactly what the depth had been before). After a bit we started heading back to the entry point, and our depth changed, and the computer *still* said 20 minutes until NDL. I knew something had to be wrong, so when we got back, I told my buddy that my computer was not working properly, and we both did a long safety stop.

The computer was permanently stuck at one point in the deco algorithm, but the depth and time were still being displayed correctly, giving the impression that it was still working. I brought it to the company that made it, and it turned out that a component had broken off of the circuit board, causing the NDL function to stop working, but leaving the depth and time still working! The computer was 10 years old, so maybe I shouldn't have been too surprised, but I always assumed that if a computer failed, it would turn off completely, not just give bad deco information. If I hadn't noticed the problem when I did, this could have resulted in going into deco without knowing it, and skipping a necessary deco stop.

 

[jeckyll]

DeepBound:

Thanks for posting this. I think it underscores a very important point: you should have your dive planned before going into the water. Hopefully it will be a reminder to some folks to do that

 

[Charlie99]

I treat ALL of my gauges as suspect.

Before checking time, depth, gas pressure, and deco status I always have a number in mind as to what I should see. Hopefully, that will alert me relatively early to a computer failure, stuck SPG needle, etc.

A wise diver does like you did, and keeps their brain engaged rather than turning it off and letting the computer do all the thinking. It does sound like you skipped one step in your pre-dive checks before dive #3 though, ----- a look at the computer and see if what it is calculating for NDL at the depths of interest for the upcoming dive, and doing both a sanity check in your head and comparing against your buddy.


Thanks for the reminder that not all gauge failures are immediately obvious.

Charlie Allen

 

[Nitrox50]

Always have a maximum bottom time before you get in the water - and after that a 20 dollar watch can save your *** the day your computer dies. The computer always fails at depth - never when you are sitting playing with at the boat.

So a back up time device can save the day and maybe even more. And does not have to be something fancy - just a cheap dive watch.

 

[Scuba-Jay]

yup a great reminder. Nothing can replace the tables and common sense. Im glad you recognised the problem and took that extra long safety stop!

 

[jeckyll]

...The computer always fails at depth - never when you are sitting playing with at the boat.

...

Mine failed on land

Seriously, I agree that having a spare bottom timer is a smart move. I'd bring a decent dive watch though. If you need it, something already went wrong and at this point the last thing I'd want would be to realize the cheap watch failed

 

[mikerault]

I dive with a spare computer (Cochran Commander, Citizen CYber Aqualand NX) and a bottom timer (on my depth gauge) as well as a dive buddy...can't be too careful!

Mike

 

[DeepBound]

I dive with a spare computer (Cochran Commander, Citizen CYber Aqualand NX) and a bottom timer (on my depth gauge) as well as a dive buddy...can't be too careful!

Mike

I want to get a watch-size computer now, to make it easier to keep two on my wrist and compare them. I still can't believe that the computer kept working as a guage but the NDL got stuck at 20 minutes left.