Need backup computer advice please

[Mr Carcharodon]

I dive two computers and don't understand why others don't do this as well.

What problem are you solving with the backup? Not a flame, a serious question.

 

[Crush]

What problem are you solving with the backup? Not a flame, a serious question.

As I indicated, the backup computer is a more functional version of a bottom timer. Bottom timers are of course a good idea as a redundant depth gauge.

 

[jhelmuth]

So the problem you are solving for is: "your computer fails"?

 

[donnad]

Thanks all. Your comments have helped. I've always thought having a backup is a good idea, but the reason I really want one on this trip is this. Last year hubby changed the battery on my computer and it wasn't sealed back up properly and flooded on Bonaire. Dive shop there cleaned it out and it worked fine the rest of the trip. Went to Mexico on memorial day, it was fine. Now I get it out of the closet and it won't come on. Went to the dive shop, got new battery, they cleaned it up, put a new o-ring in it, and all seems well. So........I will be a little skittish that it might flood. So I may use the new computer as a primary and let my xr2 be the backup. I have an spg and a dive watch, so I could switch to tables, but only after sitting out cause i'm diving nitrox. I'm thinking of getting the aeris manta.......I need to see what the difference in the old and new one is.

 

[fnfalman]

Serious question: how do you know which computer is malfunctioning if either of them are not just plain dead? If one of them conked out, then obviously that one doesn't work.

But if one of them were to display wrong readings, then how do you know which is the correct one? If one's depth said 100-ft and the other said 115-ft, which depth reading is correct? Or are you now have to take an analog depth gauge as a backup to the backup? Which one's keeping the correct dive time? Or are you now have to carry a bottom timer or a mechanical watch to back up the backup?

 

[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

...

Serious question: how do you know which computer is malfunctioning if either of them are not just plain dead? If one of them conked out, then obviously that one doesn't work.

But if one of them were to display wrong readings, then how do you know which is the correct one? If one's depth said 100-ft and the other said 115-ft, which depth reading is correct? Or are you now have to take an analog depth gauge as a backup to the backup? Which one's keeping the correct dive time? Or are you now have to carry a bottom timer or a mechanical watch to back up the backup?

The question remains unawswered...

 

[Randy43068]

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??? I was looking at the Mares Puck maybe or the Aeris Manta?? Trying to keep the cost down on this. Help please. Thanks in advance.

if you really have to have one, get the cheapest damn thing you can find.

 

[jhelmuth]

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.

Nice try on "deco" mincing... the context was intended to be understood how deco can be different on 2 different computers (IE - different models). If anyone does not understand that ACTUAL obligations (on your body) are in fact different for any given individual and different even for the same individual on any given dive. If you fail to understand that, you shouldn't be commenting. Don't try to make it sound as if I'm less than competent in that respect by trying to give some greater level of detail (which you failed to do given that you did not point out the additional variations in obligation among divers and even the same diver among any set of dives).

You are correct... I am of the opinion that "backup" dive computers are typically unnecessary. However, you probably fail to know that I do not consider that practice completely unnecessary. While I believe there are other options, I am a believer in evaluation of each dive and the merits of what gear you might choose to address a problem or need. (so you did "guess" a bit wrong there too...)

I also commented on the particulars of algorithm matching and offer some ideas about how that might actaully matter. Options are good.... (please go back and take the time to read what I actually said on the subjuect to the OP).

BTW... I am a long standing member of DAN (Pro) and I buy their highest level of insurance (Master) and I buy travel insurance (durring most months of the year - but not all). And I DO feel very comfortable diving my gauges as a backup to my dive computer.


I do not try to make a point saying you are wrong in your practice - I not only accept it, I believe you should do what you feel is best. I only offer another opinion with somethings to consider as a way to offer others the chance to think through their dive planning and execution.



All the best!

Jim

 

[jhelmuth]

As I indicated, the backup computer is a more functional version of a bottom timer. Bottom timers are of course a good idea as a redundant depth gauge.

Speaking of redundancy...


Have anyone here considered "what if" the backup computer fails? Doesn't that mean you need to have some backup for the backup? With gauges (a bit more reliable and you can't "bend" them) I don't see how that is an issue. IE - even if the gauge fails, you can replace it instantly without interuption to any of your dive plans. Not so with a "backup" computer (you'd just be doing the same thing as having backup gauges in the first place).

 

[Crush]

jhelmuth,

What you wrote was:

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)...

which I took to mean that you felt it would be very difficult to get two different computers to react differently on a dive. I pointed out that computers with two different algorithms can behave very differently on the same dive - try pairing a Suunto with a Sherwood.

Nice try on "deco" mincing... the context was intended to be understood how deco can be different on 2 different computers (IE - different models). If anyone does not understand that ACTUAL obligations (on your body) are in fact different for any given individual and different even for the same individual on any given dive. If you fail to understand that, you shouldn't be commenting. Don't try to make it sound as if I'm less than competent in that respect by trying to give some greater level of detail (which you failed to do given that you did not point out the additional variations in obligation among divers and even the same diver among any set of dives).

Pal, I only commented on what I read on the page - I can't read your mind. And I am not the one making you sound less than competent.

Keep flaming away, jhelmuth - I may read your posts on this thread over a cool one, but I won't be responding. Be sure to point out that I have far fewer dives than you - it will feel good. I won't point out our disparate educations.