Are dive computers making bad divers?

[boulderjohn]

I had a watch who’s minute arm started swinging freely during a dive.

I used to use a dive watch when teaching pool classes so I could keep track of the time while doing the deeper parts of the classes. On two different occasions, I had something far worse than a swinging minute arm. On those two occasions, I was feeling that things were going remarkably well in terms of getting done in a timely fashion, but when we came up from that portion of the class and I saw the clock on the wall, I saw that my watch had suddenly gone wrong. In each case, it was at least 10 minutes slow. It had apparently stopped for a while and then restarted. It was working just fine when I looked at it, but it had somehow lost that much time.

The only problem for me on those days was a slightly messed up class schedule, but if I had been using that watch to time a dive while using tables, I could have been seriously screwed.

I have been using a computer since about my 20th dive a quarter century ago, and I have never had a failure while I was diving. I did own a very defective Uwatec for a while that would kill its battery while it was being stored between dive trips, but I never used it for anything other than a backup. It was later recalled, but I was never notified and did not find out until after the allowed period for replacement, and so it just became a paperweight.

 

[boulderjohn]

I never or still don't carry 2 watches, but on complex deep working dives we had the safety of a standby on the surface who would also have your time. Stops were done on a fixed cradle so you could complete the dive without watch or depth gauge. How would you rate the reliability of modern computer in your experience.

As I wrote while this post was being made, I have used computers for a quarter century. I had a defective Uwatec that was recalled without my being notified. It was my original backup computer, and it did not last long. I have never had any other problem with one. As I also just wrote, I have had more dive watch failures than computer failures, and I only used dive watches while doing pool instruction.

 

[Celt]

As I wrote while this post was being made, I have used computers for a quarter century. I had a defective Uwatec that was recalled without my being notified. It was my original backup computer, and it did not last long. I have never had any other problem with one. As I also just wrote, I have had more dive watch failures than computer failures, and I only used dive watches while doing pool instruction.

Thank you.

 

[EFX]

Big difference is that it is not recommended to follow your buddies computer.

Erik

Why? For newbies it's good advice because their likely to go deeper than their buddy or worse, stray and loose their buddy. As an experienced diver I would dive my buddy's computer making sure I stay close and at the same depth or slightly shallower. If I was really concerned I'd come up to 30 ft where I'd get more NDL than l would have gas. For the second dive I would fire up the backup and set it for more conservatism. I would never let a failed computer ruin a dive or a day of diving. My $0.02.

 

[BRT]

Why? For newbies it's good advice because their likely to go deeper than their buddy or worse, stray and loose their buddy. As an experienced diver I would dive my buddy's computer making sure I stay close and at the same depth or slightly shallower. If I was really concerned I'd come up to 30 ft where I'd get more NDL than l would have gas. For the second dive I would fire up the backup and set it for more conservatism. I would never let a failed computer ruin a dive or a day of diving. My $0.02.

Why not just carry the backup with you and not worry about conservatism?

 

[RIHappyDiver]

Why? For newbies it's good advice because their likely to go deeper than their buddy or worse, stray and loose their buddy. As an experienced diver I would dive my buddy's computer making sure I stay close and at the same depth or slightly shallower. If I was really concerned I'd come up to 30 ft where I'd get more NDL than l would have gas. For the second dive I would fire up the backup and set it for more conservatism. I would never let a failed computer ruin a dive or a day of diving. My $0.02.

Your question and your statement are two different things. I stated what, as far as I know, every agency would recommend to any diver of any level. If your asking why they state that, you answered the question when you discussed newbies. If your asking why I made that statement, the answer is because 1) it is what's recommended, 2) as this is the Basic Scuba forum, there are many newbies reading it.
My local diving is rarely over 40', and usually closer to 25', so I'll dive all day without a computer if it comes down to it. Trips, on the other hand, are generally 4-5 dives a day for 6 days. I'm taking a backup computer on each dive, unless one of them goes belly up, then I'm diving with one that has my history for the week.

 

[Belzelbub]

How would you rate the reliability of modern computer in your experience.

Modern computers are very reliable. As with everything, there are sometimes teething problems. Scubadada probably has the most detailed records. In his case, the computer is over 99% reliable. But, as I recall from previous posts, the majority of those failures were due to user error, or dead/bad batteries.

I don’t have nearly that many dives, but haven’t had a single in-water computer failure. I have had two failures out of the water. One was a computer that just died. Dead battery, and didn’t wake up after the battery change. One was a bad transmitter. I bought it used, and it just didn’t fire up.

Electronics tend to fail on startup, so if it fires up and works, there is a very good chance that it will continue to work during the dive.

 

[Belzelbub]

Why? For newbies it's good advice because their likely to go deeper than their buddy or worse, stray and loose their buddy. As an experienced diver I would dive my buddy's computer making sure I stay close and at the same depth or slightly shallower. If I was really concerned I'd come up to 30 ft where I'd get more NDL than l would have gas. For the second dive I would fire up the backup and set it for more conservatism. I would never let a failed computer ruin a dive or a day of diving. My $0.02.

I would say it depends. Diving without a computer has much simpler calculations. You are really only worried about max depth, and time. Knowing that the entire dive is not spent at that max depth, there is a significant buffer built in.

A computer, however, is tracking more real time, so relying on a computer that is not with you is less safe. How much so depends on the dive. If the buddy’s profile is riding the NDL, relying on that computer is much more risky.

For me, using a backup computer that isn’t on all the dives is asking for trouble. Most dive computers don’t have enough conservatism to account for that.

 

[Stoo]

I'm guessing that is why Stoo thinks computers should be sold in pairs.

However, even if computers don't match up exactly you are OK to follow one and keep the other as a backup. T

Because I used to dive solo most of the time, wearing two computers was pretty normal. When I had various TUSA/DIVE RITE/ETC pucks, they had a pretty high failure rate, and even though they were the same model computers, they rarely matched.

Mrs Stoo and I own three Shearwaters currently. They are never more then 2 or 3 seconds different, but whan I used mismatched computers, I'd just keep favouring the most conservative. NDLs aren't something that I run into much. All of our diving is decompression diving. Even on vacation, we routinely go in to a bit of deco on most dives. But we dive very conservatively. If the computers say 5 minutes of deco. we'll do 10 or even 15, then a few more for good luck. I will hang out in 15' until my tank is mighty low.

 

[Wibble]

It's actually very hard to make a mistake of an entire group as when you're planning dives consistently with tables a mistake jumps out, but there has to be a reason people carry backup computers. Unless of course its to sell 2 computers instead of 1. I don't recall a recommendation to carry 2 watches or depth gauges.

It’s not the planning, it’s the reality you find when you’ve descended to the dive site. You plan for a scenario but then discover the site is nothing like that.

Computers give you huge flexibility compared with tables. If you’re diving a rebreather then this basically removes gas limits (given the right diluent and bailout). Your dive plan then becomes the max dive time, using your computer’s TTS as the guide.

Thus if you’ve been lurking 10m/33ft deeper it doesn’t matter.