Should I carry a backup computer?

So I had been shopping over the last couple of weeks to get a complete set of gear together for me and my step dad so we don't have to rent equipment that often.

One of the steals that I got was an Oceanic Prodigy Imperial Dive computer which had 4 dives logged on it with a ton of other stuff including fins, bag, tusa mask, boots, 2 gauges with compass and one set of 1st and 2nd stage regulator.

Since the Oceanic is not nitrox capable and we plan on diving with nitrox while in FL we got some Dacor Darwins the other day.

I did replace the battery in Prodigy and regreased the o-ring and took it diving with me at the local quarry, works like a charm and has the same info as the other computers that we were using that day.

Question now is:

Should I keep the Prodigy as a backup air computer incase the Dacor Darwin fails me (doubt it) or gets somehow lost damaged while underwater?
I would need to buy a wrist or hose boot to get the thing mounted to the gear somehow. I did have it with me inside the BCD pocket which was velcroed closed.

What does everyone think?

It can't hurt to have one, but if the first one fails underwater, the dive is thumbed anyways

After I bought a Nitrox computer, I dove with my old air computer as a backup for awhile. I pushed the air computer when diving Nitrox (like I wouldn't have done if I were really diving air) and occasionally sent it into a bit of deco. I would do the stops to keep it happy and useful as they were never a problem to do anyway. (After awhile I got tired of doing that and bought a second Nitrox computer, for my diving the backup is worth it to me.)

Scubastud16:

It can't hurt to have one, but if the first one fails underwater, the dive is thumbed anyways

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I understand where you are coming from with this thought...but it would also depend on how the computers are used.

Myself and a number of divers I know that are, shall we say, advanced in years, dive nitrox but dive our computers in a normal air mode. That gives an additional safety factor we prefer. It may not be what you want to do, then ok, dont. But, I dive two computers both set on "air" and if one dies that is no problem and it isnt the end of the dive. If both die on the same dive, then it is probably the end of the dive.

An air computer used for nitrox dives will misreport CNS Toxicity and OTUs, perhaps making it more dangerous than it would otherwise be. If you want a backup computer, get one that can track what you are actually diving.

The backup computer *should* be the one strapped to your wrist. Your primary should be between your ears.

Scubastud16:

It can't hurt to have one, but if the first one fails underwater, the dive is thumbed anyways

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since there's a smiley I'm assuming this was a joke. If your backup computer goes you're no worse off than someone who didn't have a backup computer to begin with.

PerroneFord:

An air computer used for nitrox dives will misreport CNS Toxicity and OTUs, perhaps making it more dangerous than it would otherwise be. If you want a backup computer, get one that can track what you are actually diving.

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well no, they won't misreport it, they're not going to report it at all. But generally you would be using the Nitrox computer. And I'm talking rec diving here, you'd have to be doing some rather intensive rec diving for accumulated toxicity to ever be the controlling factor. The rest is taken care of by knowing your MOD and doing reasonable surface intervals. This stuff is also trivial to figure out from previous depths and times and continue diving with no extra time sitting out or anything, if you're worried about it. Unlike NDL, which is not so convienient when you're doing multiday-multidive-multilevel diving. Diving Nitrox on air tables or computers is something people do for conservatism sometimes anyway, and was a topic covered in my class, anyway.

The backup computer *should* be the one strapped to your wrist. Your primary should be between your ears.

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sigh, here we go with that again. I would say recognizing what you really need to track and how to do it is using one's brain more than a blanket statement that it shouldn't be done.

Damselfish:

since there's a smiley I'm assuming this was a joke. If your backup computer goes you're no worse off than someone who didn't have a backup computer to begin with.

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It isn't a joke at all. I said "the first one" for a reason, meaning his primary computer. If your primary computer failed, the dive is done (or should be).

Damselfish:

And I'm talking rec diving here, you'd have to be doing some rather intensive rec diving for accumulated toxicity to ever be the controlling factor.

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Several repetitive dives (like on a liveaboard) to depth on certain mixes would be a pretty easy way to rack up partial pressures over the limit.

Again, a general statement receives specific criticism. Welcome to SB.

sigh.

PerroneFord:

An air computer used for nitrox dives will misreport CNS Toxicity and OTUs, perhaps making it more dangerous than it would otherwise be. If you want a backup computer, get one that can track what you are actually diving.

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CNS toxicity is not a problem if a few simple rules are followed.

Assuming you are using 32%:

Do not go deeper than 111 feet (pO2 of 1.4)
Do not go into deco.

Really that is all there is to it.

NDL at 110 feet for 32% on my computer (Aeris) is 25 minutes

Total daily allowed time at a pO2 of 1.4 is 180 minutes. If you use a sensible 80% of maximum that gives you 144 minutes.

Which implies that the final rule is no more than 5 dives in a day(144/25 =5.76).

Obviously anybody diving nitrox should understand CNS toxicity,but in practice you are not going to exceed the limits doing recreational profiles.