Forgetting to turn on computer before the dive

[Hoyden]

Actually, you still need to check it’s on prior to submerging as some computers will time out and turn off if no activity detected in a set period - my Teric does that.

Your Teric should wet activate even if turned off. I just went and tested mine and it wet activates even if not turned on,

 

[Gandalf-the-Diver]

Both my computers turn on by themselves. Zoop backup in a console, which I never turn on; does it by itself, and my Peregrine on my arm. It will turn on by itself if I do not turn it on.

 

[Joneill]

Your Teric should wet activate even if turned off. I just went and tested mine and it wet activates even if not turned on,

Yes - it will, but I still like to make sure it’s on before I submerge.

 

[Belzelbub]

Your Teric should wet activate even if turned off. I just went and tested mine and it wet activates even if not turned on,

Correct, though it's technically not a wet activation. The Teric and Perdix (and I assume the rest of the SW line) don't have wet contacts. The activation is done based on an increase in pressure.

Yes - it will, but I still like to make sure it’s on before I submerge.

And that's a good idea. All the computers my family uses have some sort of automatic activation (Oceanic, Garmin, and Shearwater). Though I'm pretty sure all of them don't recommend relying on it. If only diving air in the same mode, probably not a big deal, but if you change gas and use different modes, you'll at least want to confirm mixes and settings.

My Garmin will activate automatically, and will use the most previously used dive mode and settings. So, if I used Apnea previously, that's what will launch. Plus, there is another negative with relying on this with the Garmin. Dive entry location won't be saved. When you start the watch in the appropriate mode, it takes a few seconds to find the satellites and get a position. No signal underwater, so no entry location. On those dives, only exit will be saved.

 

[RobPNW]

What's the thing on some computers you want to avoid where they may lock you out for the day? Is it gauge mode?

 

[boulderjohn]

What's the thing on some computers you want to avoid where they may lock you out for the day? Is it gauge mode?

In some computers, if you go into deco and do not follow their guidance, they will go into what is sometimes called error mode. In error mode, it will function as if it is in gauge mode. It will just give you the basic information (depth, time, etc.) with no algorithm-based guidance.

Here is an example from my own history.

My first computer was a Suunto Cobra, an air-integrated (by hose) computer with that feature. It also did not automatically adjust for altitude. You had to set that manually. I stopped using it and went to a wrist computer instead. I went to Florida for an extended stay. I decided to pull that Suunto out of storage and use it as a combination backup computer and pressure gauge. On the second dive of a 2-tank trip in Florida, my mind wandered to how long it had been since I had used that Cobra, and I recalled that my last usage was in the Denver area. Oh, crap! It's set to high altitude! I looked and, sure enough, it had me in deco, while my wrist computer, with an accurate altitude reading, had me well within NDL. If I didn't follow the Suunto's guidance, it would go into error mode, and it would not function as a computer for a couple days. It would still give me the pressure readings, and that was all I needed it for, so I went ahead and surfaced when it wanted me to be doing a deco stop. Sure enough, it went into error mode, but that was fine with me.

 

[SlugLife]

I suppose it's a very basic question, but although I've searched for the answer on the forum, I haven't found any. The closest thing is having a computer which fails in the middle of a dive, but I don't know whether the situation would be exactly the same.

It's never happened to me, but yesteday, I suddenly asked myself what should be done if you forget to turn on your dive computer before jumping into the water. Should you turn it on immediately as soon as you realise? Is there a time or depth lapse when you can ignore its not having recorded data? Or would it give an error message as it notices it's not the beginning of the dive? Should you abort the dive? Trust your buddy's computer, as long as it's your first dive that day and also his? Cancel any other dive you intended to do on the same day?

Thanks if you can clarify this for me!

(I'm probably repeating most of the responses.)

The vast majority of modern dive-computer auto-turn on when you hit the water. The few that don't tend to be older dive computers, and they turn on fairly easily by hitting a button. If it's off, just turn it on.

As far as deco:

I assume your normally do no-deco recreational diving? If you're mostly sticking to 60ft (20m) or less, single-tank dives you have practically nothing to worry about. Just do your dive as normal, do your safety stops. If you're concerned, do additional or longer stops. Taking a somewhat worst-case kind of scenario, where you do a 1-hr 60ft dive, ascend 30ft/min, and skip your safety stop, you might feel light-headed on the surface. Not saying I recommend skipping safety stops, etc, but if your computer was off for 15 minutes during a 60ft or less dive, it's not a big deal.

If you're diving 90ft+ (30m+), you should REALLY have a dive-plan. With that dive-plan, you should also have a plan for about how long you intend to be at depth, and what stops you intend to do on the way up. You might also consider a better/newer computer that auto-turns itself on, if you're doing deeper dives.

 

[ElizaDoolittle]

Yes, it's no-deco diving. And all my dives are short (I don't think I've ever gone beyond 40 minutes), as I'm not good enough yet not to run out of air. My maximum depth is around 30, tough most times I stick to the 18m most diving centres assume an OWD should be doing (being an ACUC OWD, and having now over 30 dives, I could dive down to 40m or whatever the maximum depth according to the place's law is, but since I don't need to boast of going deep to massage my ego, I'm perfectly happy going to PADI's maximum depth of 18m, as most people seem to believe it's PADI who sets the rules for all divers). But even for a 18m dive, I always ask the guide or whoever is in charge of the dive to explain to me the planning in depth, because I believe that knowing what I'm doing will help me make my own decisions whenever I feel I'm prepared to plan my own dives.

I haven't tried my Leonardo yet to see whether it automatically turns on when I start a dive (funnily, the two or three times I've dived since I posted my question, I forgot not to turn it on before!), but from all you've said, I think it'll do so.

 

[Blackcrusader]

What's the thing on some computers you want to avoid where they may lock you out for the day? Is it gauge mode?

No, it is exceeding NDL and going into Deco then not doing the required deco obligation.

 

[Blackcrusader]

I'm perfectly happy going to PADI's maximum depth of 18m, as most people seem to believe it's PADI who sets the rules for all divers). But even for a 18m dive, I always ask the guide or whoever is in charge of the dive to explain to me the planning in depth, because I believe that knowing what I'm doing will help me make my own decisions whenever I feel I'm prepared to plan my own dives.

PADI and other agencies have stated that the recreational limit for OW outside of the training environment is 40m. 18m only applies to OW student divers during their courses. No agency can decide your dive depth limits once certified. Staying shallow if you have high gas consumption is always a good thing. You should have been prepared to plan your own dives during your OW course.