Need backup computer advice please

[JohnB47]

One reason to have a backup is so that you still have a working computer if the primary fails. Another is to check whether or not your primary is working properly. When a computer fails, it may not fail hard - it could just give incorrect readings. If you have two computers that use the same algorithm, a quick comparison will give you a pretty good idea whether they are working properly. If you make multiple dives with computers with different algorithms, the two could get so far out of sync with each other that you would have no idea whether they are working right or not.

 

[jhelmuth]

One reason to have a backup is so that you still have a working computer if the primary fails. Another is to check whether or not your primary is working properly. When a computer fails, it may not fail hard - it could just give incorrect readings. If you have two computers that use the same algorithm, a quick comparison will give you a pretty good idea whether they are working properly. If you make multiple dives with computers with different algorithms, the two could get so far out of sync with each other that you would have no idea whether they are working right or not.

Q: So how would you know which one failed, and which one to use (in your above scenario)?


I agree you'd know one is likely to not be working (assuming they - primary and backup - are the same), but beyond that, I fail to see the benefit if I can't identify and eliminate the problem computer.

Jim

 

[Scared Silly]

While I would agree that a full on back up it not necessary for recreational diving it is nice to have redundant depth gauge bottom timer. Which would then allow you to back out your dives to tables so that you could continue to dive in case your primary fails. For that we have a dive watch (Suunto D3). Small enough that it can be worn as a real watch yet functional under water.

While there are pros and cons to using multiple computers one thing that I do like about having same brand computers is that the menus are typically very similar. Which makes using them a bit easier to figure out. Like when diving nitrox and having to switch the gas mixes.

 

[jhelmuth]

While I would agree that a full on back up it not necessary for recreational diving it is nice to have redundant depth gauge bottom timer. Which would then allow you to back out your dives to tables so that you could continue to dive in case your primary fails. For that we have a dive watch (Suunto D3). Small enough that it can be worn as a real watch yet functional under water.

While there are pros and cons to using multiple computers one thing that I do like about having same brand computers is that the menus are typically very similar. Which makes using them a bit easier to figure out. Like when diving nitrox and having to switch the gas mixes.

+1.... all good points!

 

[ianr33]

For a single recreational dive agree that a backup computer is not necessary. I would not be happy though if after 3 days at Cocos Island/Galapagos/Truck my computer died and I was forced to either sit out some dives or try and figure where I was on tables after multiple 100 foot dives.

For exotic trips a backup computer is cheap insurance compared to the cost of the trip.No need for anything fancy. My opinion is the algorithm should be the same or more aggressive than the primary.That way you can just forget about it until its needed.

I've had 3 total computer failures in maybe 400 dives. One of them was at 160 feet in Bonaire.It does happen.

 

[jhelmuth]

For a single recreational dive agree that a backup computer is not necessary. I would not be happy though if after 3 days at Cocos Island/Galapagos/Truck my computer died and I was forced to either sit out some dives or try and figure where I was on tables after multiple 100 foot dives.

For exotic trips a backup computer is cheap insurance compared to the cost of the trip.No need for anything fancy. My opinion is the algorithm should be the same or more aggressive than the primary.That way you can just forget about it until its needed.

I've had 3 total computer failures in maybe 400 dives. One of them was at 160 feet in Bonaire.It does happen.

I've had zero failures in over 1200 dives... BUT YES - they can fail.

I too agree I'd hate to sit out dives on a trip (and that might be a good oportunity to just rent a backup from the dive op over the length of the trip - ez peezy)

Did you actually mean that you want the backup to be LESS agressive (or same) as primary?

 

[ianr33]

Did you actually mean that you want the backup to be LESS agressive (or same) as primary?

No. I would want the backup to be same or MORE aggressive. That way you just follow the primary and forget about the backup. Put it in a pocket out of the way if you want.

If the primary were to fail you know the backup will be OK with your N2 loading.

If the backup is less aggressive you would need to keep checking it during dives to make sure its not bent. Not really a backup at that point.

If you end up diving the aggressive backup you don't have to dive it all the way to NDL.

 

[GrumpyOldGuy]

I dive with a backup for another reason, essentially a calibration and functional check. A basic puck computer is not all that expensive ($250 or so if you shop smart).

With 4 similar computers in the family, I can rotate which one as a backup and compare it to my primary. If one of the 4 computers starts to have problems (I.E. does not match depth and RNT), it becomes clear instantly. It a lot easier than to send a computer someplace for "maintenance" and the associated shipping cost. It gives me a high level of confidence in addition to possibly saving some dives on a boat trip.

 

[scubadada]

We have a trip coming up and want to get a backup computer...........just a wrist model with nitrox capability. Husband has an Aeris Elite T3 and I have the Aeris XR2. So we've been on the same algorithm. So we should have the backup be the same algorithm, right???

Yes, or your dive will be controlled by the more conservative computer. You will have to satisfy any deco you accrue to clear it or risk losing your backup for a day, defeating the purpose. I would get another Pelagic Pressure Systems computer.

If you dive your current computers very conservatively, maybe it really doesn't matter what your backup is and you can simply follow it. Really depends on your diving style. I dive Oceanic VT3 and have an older Geo for backup. I tend to push the NDL limit.

I don't want to miss dives or dive time on a trip because my computer and it's dive memory are lost. I've had 1 computer failure and that made having the back up more than worth it. I've also had a couple of altitude sensing errors that became quite obvious having 2 computers.

Good diving, Craig

 

[Crush]

True... but you'd have to really be into some deco on the primary for that to happen (and/or blow off your safety stop)...

No. "Deco" (as calculated by the computer) is the result of a model of the human body - you may really be in deco, or you might not be. Different algorithms give different results. One computer can be in deco, one can be not in deco, and your body could be either.

jhelmuth, it seems as though you think backup computers are a waste of time and money - this is your opinion. However, the OP asked for advice on which model to choose and whether or not algorithm matching is important. You may think that a backup is a waste of money, but my backup computer cost $320 while a digital bottom timer was selling for $150 - the extra $170 for an actual computer seemed like an easy choice to me.

Finally, if your only computer was to fail catastrophically before you were able to record your dives that day, you would be unable to dive tables for 24 hours (according to the recommendations of most agencies) if you were unsure of your residual nitrogen (which you would not know if the day's dive information was lost). With a backup you just keep on diving - especially useful if you are in the middle of a seven day liveaboard excursion.

Is a computer failure likely? No. Is an accident likely? No. If you are the kind of person that buys travel insurance? If yes, you might also get a sense of security from a backup.