Back up dive computer

[g1138]

+1 to the comments made by vladimir. I also like what Charlie99 had to say (as usual).

@g1138: Eh? Computers only lock-out (if lock-out is incorporated into the design) when the user surfaces with an unfulfilled deco obligation.
If one computer dies, then you use the other one. No conflict at all.
Diving two computers which use different algorithms only "works" if the user ensures that the dive profile doesn't violate the more conservative computer.

Yup that is true. I was speaking in a worst case scenario; perhaps lockout wasn't the best choice of words. It'd be my preference, if I had 2 different dive computers, to dive the more conservative one as my primary.

Edit: I was re-thinking about this example carefully before posting.
You're nearing deco and your primary comp goes out. You're conservative backup is already into deco. You weren't planning on going into deco and you don't have the air to do a deco stop (cause you're an idiot). So you ascend, safety stop, and skip deco (as your liberal primary computer would have just listed a safety stop).
Now you have a dead primary and locked out back up.
Unlikely, but possible?

PS Not meaning to imply anything by using the word "you"

 

[Tortuga68]

You should have ascended before putting your backup into deco; doing so negates the point of having a backup

 

[Spazzy]

Most recreational divers only carry one computer.

Most deco divers carry a second computer and/or a gague with tables/run slate.

 

[EastTNDiver]

First of all, I would like people's opinions on when a second dive computer is absolutely necessary and is it a good idea for most situations (within rec limits)? I know you would have to wear it on every dive for it to correctly calculate everything. What about two different brands? They would most likely use different algorithms and therefore have different no stop times among other things. Would this be ok? Or is this not recommended. I am new to diving and am trying to learn as much as I can. So I am looking at computer failures and what to do.

You don't necessarily have to "wear" it. My backup is a puck style where the computer can be removed from its wrist mount. I keep it in a pocket so that it records the same profile as my primary. I'm not so worried about having it so that I can continue any given dive if my primary fails. I take the backup so that I can continue diving uninterrupted while on a week's worth of repetitive diving...especially when on liveaboards. If my primary were to fail, I would probably just end that dive, put the puck back in its wrist mount during my SI, and pick right back up with the next dive.

Also, while it's not mandatory to use the same brand for your backup, IMO it's preferable to at least pick a backup that uses the same algorithm...and, that's probably just easier if you stick with the same brand.

 

[Tortuga68]

I think we can take 'wear' as meaning 'take it along'... although personally I would wear it, if you do have a failure you don't have to fiddle around/thumb the dive, plus you can make sure you keep both of them out of deco - and lastly it's interesting to see/know what the differences (if any) are in depth reading, NDL, nitrogen loading & other data

Might be worth mentioning here that if you use EAN you should set both computers, if you choose to use two, to the correct mix or your backup isn't going to track your nitrogen loading correctly

Agree about your second point, since there are other advantages to using the same brand and/or model - same battery kit, screen protector, strap/mount etc not to mention not having to remember two sets of operating instructions, display layouts, warning sounds/symbols and so on

 

[Kenny13]

My son-in-law ended up getting 2 computers when he recently purchased all his gear. That wasn't his original plan, as he was only going to get a wrist model. However, when he was at the LDS putting together his package he found out that they offered the SPG/depth gauge console he wanted with the identical computer to the wrist model he was getting for only like $40 more than just the SPG/depth gauge alone so he decided to spend the extra $40. Also, he's got 2 of the same model so he doesn't have to worry about one being more conservative than the other and he still only has one on his wrist.

I think I probably would have done the same thing if I were in his shoes. Although we don't get to dive as often as we'd like, at 200+ miles one way I'd hate to have a trip end due to computer failure. Eventually as I accumulate more gear and hopefully get to log considerably more time underwater I'll probably add a second computer, but it's not high on my list of priorities right now.

 

[Straegen]

For most rec diving, carrying one is very acceptable and as some have mentioned carrying zero is fine too. The only time I have seen a computer die, the other diver piggy backed off the groups computers. I think he did his own table calculations but only as a double check. I cannot outright recommend this as circumstances differ from dive to dive and boat to boat. I personally carry an extra SPG, watch with a depth gauge and a set of tables just in case.

 

[tbone1004]

was doing a dive at little river with my cave instructor and for some reason we forgot to set the second gas on our computers and they assumed we were on 50% or something weird so we're at our deco stop with 20 minutes deco left. Should have had 5. After 7 we both looked each other, shot ourselves in the mouth, pulled tables out, saw we were fine and left the computers to decompress without us. Not ideal but our tables were happy so we did a surface decompression for 15 minutes and chilled out talking to another dive team.
That being said, I rarely use my computer in computer mode unless i'm doing a lot of repetitive dives with non square profiles i.e. cave weekends and open water training.
No backup computers needed for most of my stuff so I don't have one. I have 3 computers, all nitrox and all will do deco, but one is a different algorithm and I don't really like the other one all that much... Text is too small If you're competent with tables though it's really not practical to have two for most dives especially if they're different algorithms. Take tables, analog depth gauge and a watch with you as a backup. Small enough to stick in a pocket somewhere and no worries

 

[fdog]

If you are on one of these

Take two computers. It's cheaper than missing a day of diving.


All the best, James

 

[cloudflint]

Over winter the cold actually killed the battery in my dive computer which was a bit annoying. Considered setting myself up with two computers but figured if the cold could kill one it could kill two so I now have a watch and analog depth gauge and a single computer. I use the analog gauges since I dive tables most of the time anyway so my computer functions as a backup depth and bottom timer. I think if i was on a diving holiday or something though i would take two computers so i wasn't having to calculate everything on square profiles