backup computers: several questions-need opinions

[GrumpyOldGuy]

I am in the camp of using the same exact computer. My reasoning is a little different. Even if the computers use the same basic algorithem, there are subtle variables (typical things such as pads to add more safety and proprietary tweaks) the will make the results different.

If you have 2 different computers, one tends to become the primary and one a backup. It nice to have backup, not critical but can save the dive trip.

If you have the same 2 computers, you then have a check in place if one of the most error prone components, the pressure transducer goes out of calibration. This puppies record the depth (and the altitude before the dive in some models). They can drift and give you bad information without you knowledge if they are a bit off. If you have 2 identical computers and one started reading more shallow you know you have an issue and use the deeper reading one (more conservative). If they read the same (with a foot or two) then you have confidence the data is good. The other part of the computer (like the clock) are purely digital and tend to work correct or fail totally, not drift.

 

[Peter69_56]

Seriously? Until a few years ago, charts that just look at your max depth range were sufficient. The rule that if your computer malfunctions, you must end your dive and cannot use your buddy's is just an ad for computers. A back-up computer is a very expensive redundancy. How about ensuring that computers work? My Suunto Vyper died after 60 dives but out of warranty. Suunto offered me 5% off a new one. I bought a Cobalt. If it dies amid dive, I will go no deeper and surface with my buddy when my air gets to 700 as I normally do unless her NDL gets short - which rarely happens on our Nitrox, touristy dives.

The fatal assumption here is that you will stay with your buddy until the end of the dive. If you dive in poor vis and it fails you both should abort the dive. The number of times my wife and I have near been separated under low vis and turbulent water. We dive with sufficient gear to be able to surface independently if needed whether doing rec dives or tech dives. Once you have been hit by a surge that blows you 10-15 feet up a reef into thick weed and then sucks you back down again over the edge you will see what I mean. Never assume you will NEVER lose your buddy. The worst vis I have had was 6", try staying with your buddy then. You get no warning either sometimes, you drop down and maybe at 15 metres the world goes black and you are left wondering if your buddy is still going down as planned or stopped and coming back up again. Ans here you are with no dive computer near the end of your dive wondering where your buddy is, and wondering what depth you are at, and if you are now in deco and where your safety stop will be? etc etc. Beware the unprepared, Murphy lurks at every corner.

 

[Stoo]

The rule that if your computer malfunctions, you must end your dive and cannot use your buddy's is just an ad for computers. A back-up computer is a very expensive redundancy.

Yes, seriously. Computers can be fussy things and to have one fail in the middle if an expensive vacation can cost you a day or more of diving. If the Dive Operator is aware it has failed, they will generally insist you not dive the following day. Expensive redundancy? Yes. But if it keeps you in the water, it's well worth it IMHO.

Fred, your "dead computer ascent plan" might salvage the dive safely but it won't save the day on a vacation.

I started wearing two computers as soon as started diving them. I dive solo most of the time at home, so I want redundant everything where possible. And I have yet to own a computer that didn't eventually die (well, except the ones I have now...) and I've had several different brands over the years.

As for whether your spare should be the same as your primary, I'd say absolutely. Presumably you used some logic to decide on the brand for your primary, so it makes sense to apply that same logic for the backup. Differing displays is just confusing and could lead to a scenario where you are diving computer A on Dive 1 and Computer B on Dive 2 and that likely isn't a good idea.

The one exception to this might be for those using high-end techy 'pooters. A Shearwater Petral might retail for $1000 or more so to carry two of these is big money. Most of my friends that use these carry a bottom timer and tables for backup. I'm not sure I agree with their decision however.

 

[fred3798]

I have my analog depth gauge. It tells me my max depth. I can use tables in between dives if need be. I haven't come hear my NDL even after a week of repetitive dives since I started on Nitrox. I do not generally do very deep dives. On my last rip we hung around 50 feet for most of the hour and I dove 15 times in 5 days and never got close to an NDL infraction. I am not suggesting that I will dive without my computer by design. But given that I dive twice a year, I am not losing a day due to a computer failure. Even if I do not have the computer accurately measuring ever meter up and down, if I know my max depth and I use tables, how can I be at serious risk? The tables were good enough for 25 years before computers.

 

[theduckguru]

Assuming I have two different computers with differing programs. Do I favor the more conservative, the more liberal, or try to split the two? I'd say you want two that indicate close to each other.

 

[KeithG]

Assuming I have two different computers with differing programs. Do I favor the more conservative, the more liberal, or try to split the two? I'd say you want two that indicate close to each other.

I think there are many people that would pick the computer that is giving them the answer they want to see. Often that could be a bad choice...

Especially if one of the computers shows a violation or is locked out.

 

[Jim Lapenta]

Yes, seriously. Computers can be fussy things and to have one fail in the middle if an expensive vacation can cost you a day or more of diving. If the Dive Operator is aware it has failed, they will generally insist you not dive the following day. Expensive redundancy? Yes. But if it keeps you in the water, it's well worth it IMHO.

Fred, your "dead computer ascent plan" might salvage the dive safely but it won't save the day on a vacation.

I started wearing two computers as soon as started diving them. I dive solo most of the time at home, so I want redundant everything where possible. And I have yet to own a computer that didn't eventually die (well, except the ones I have now...) and I've had several different brands over the years.

As for whether your spare should be the same as your primary, I'd say absolutely. Presumably you used some logic to decide on the brand for your primary, so it makes sense to apply that same logic for the backup. Differing displays is just confusing and could lead to a scenario where you are diving computer A on Dive 1 and Computer B on Dive 2 and that likely isn't a good idea.

The one exception to this might be for those using high-end techy 'pooters. A Shearwater Petral might retail for $1000 or more so to carry two of these is big money. Most of my friends that use these carry a bottom timer and tables for backup. I'm not sure I agree with their decision however.

It depends on what they are doing. For me on wreck dives the computer is back up to the tables I cut. Course these are for the most part square profile dives. And I use a Predator. Should I decide to get a computer to back it up it will be another Predator or a Petrel. But I have a ways to go before the dives I'm doing will make me feel like I need to do that. I'm good for now with it and my bottom timer and tables to anything less than say 200 or so.

Sent from my DROID X2 using Tapatalk 2

 

[yaml]

again - appreciate the responses; since my wife and i already have the same primary computer (atomic cobalt); i decided that we should both have the same backup computers (probably oceanic BUD); for my freediving, i will get the oceanic geo 2 since it has all of the freediving functions i need/ want AND has the same 2 NDL algortihms as the BUD - "cosistent redundancy"? great opinions and comments - as always

 

[Stoo]

The tables were good enough for 25 years before computers.

Of course they were, and I suspect that you might be able to run a "close-enough" profile in your head too, as can I. None the less, in the context I outlined... in the middle of a vacation... most operators will ban you from the water if you kill a computer. And I know for a fact that many operators will insist their divers use computers, simply because most people diving these days barely know what tables are, let alone how to use them. Us old geezers can explain the differences between USN, BSAC and DCIEM tables, but the typical 23 year old DM in Cozumel won't have a clue...

Jim, I agree completely with what you're saying. Tables don't break, and generally will get you out of the water a lot faster than most computers.

My comments were based on a vacation diving scenario... Dead computer = missed day diving.

 

[Hatul]

Yes, seriously. Computers can be fussy things and to have one fail in the middle if an expensive vacation can cost you a day or more of diving. If the Dive Operator is aware it has failed, they will generally insist you not dive the following day. Expensive redundancy? Yes. But if it keeps you in the water, it's well worth it IMHO.

Fred, your "dead computer ascent plan" might salvage the dive safely but it won't save the day on a vacation.

I started wearing two computers as soon as started diving them. I dive solo most of the time at home, so I want redundant everything where possible. And I have yet to own a computer that didn't eventually die (well, except the ones I have now...) and I've had several different brands over the years.

As for whether your spare should be the same as your primary, I'd say absolutely. Presumably you used some logic to decide on the brand for your primary, so it makes sense to apply that same logic for the backup. Differing displays is just confusing and could lead to a scenario where you are diving computer A on Dive 1 and Computer B on Dive 2 and that likely isn't a good idea.

The one exception to this might be for those using high-end techy 'pooters. A Shearwater Petral might retail for $1000 or more so to carry two of these is big money. Most of my friends that use these carry a bottom timer and tables for backup. I'm not sure I agree with their decision however.

The problem is not the current dive, which you can terminate without a computer, but subsequent dives if you're on a dive vacation and/or doing repetitive dives. When on dive vacation I take my old Vyper as well as my current Galileo and use them throughout the vacation. The one problem with this system is you have to follow the more conservative algorithm, which should be OK as I don't want to push the NDL limits anyway.

If I were buying a second computer as a backup, a good choice would be one of the dual algorithm Oceanics, and chose the algorithm which is closest but still more liberal than the Cobalt, that way you'd be following the Cobalt, not the backup.