Backup Computer went into Deco

[atdotde]

Actually, it is not too hard to produce a smililar dive profile with a 40min deco obligation: Dropbox - Screenshot 2017-05-12 10.35.58.png (this is computed with GF 40/70 (and it's the 70 that does the job). Do you have any sort of conservatism set? I don't know this particular computer but I have seen Suuntos with either conservatism or altitude mode require deco times of similar order for perfectly harmless dives (which is why here around Munich with popular dive spots at around 2000ft altitude everybody learns very quickly not to use altitude mode although the computer manual suggests it for this height).

 

[DON-PNW]

Cressi was set at SF0, I never blew a stop, I looked at the Cressi when I was doing my 15' (this was my first notification to me that something didn't add up, remember my primary HD Icon computer was not in deco, it was happy). I did 2min at 50', 10 minute stop at 17' then 34 minutes at 10'. Remember, I was using my Icon HD as primary and it never put me in deco, nor did it "request" a deep stop, I did this out of habit because of the maximum depth I achieved. Thank you Stuartv, I was not aware that breathing rate doesn't affect nitrogen absorption at any given depth (partial pressure). Lastly, while at my 17' safety stop I looked at the Icon dive profile and did do a quick analysis that showed that I should not have been in deco, my thought process was that since the Icon had AI that it had more information then the non AI Cressi Leonardo, also none of the other divers where in deco (I know there are difference hence we don't share computers) , and after looking at my dive profile I felt fairly confident that I was not in deco, however, I don't know everything, followed my training that said to follow your computer (working or not), and as a training experience of doing a long safety/deco stop, I decided to complete the deco obligation that the Cressi computer was asking for.

 

[Kodad]

Just curious, when one dives with a back-up computer is it recommended that they be the same model (or brand)?

 

[scubadada]

Just curious, when one dives with a back-up computer is it recommended that they be the same model (or brand)?

It certainly is the easiest if your two computers match, it's the decompression algorithm rather than the model or brand. If they do not match, your dives will be controlled by the more conservative computer, either NDL or deco obligation. Many computers will lock you out for a period if you do not satisfy your deco obligation and you would lose the use of that computer. If you don't mind following the more conservative computer, then it makes no difference.

I dived an Oceanic VT3 primary with a Geo2 backup for about 6 years. They were matched within a minute of each other running DSAT. Last summer, I switched to a Dive Rite Nitek Q backup to gain experience with Buhlmann ZH-L16C with gradient factors. The mapping between DSAT and Buhlmann is not perfectly straightforward but I can now get them quite close and have learned a lot for future use. Sometimes my dives are controlled by the VT3, sometimes by the Nitek Q. When my seven year old VT3 finally bites the dust, I will almost certainly switch to a primary computer running Buhlmann.

 

[KeithG]

Just curious, when one dives with a back-up computer is it recommended that they be the same model (or brand)?

It does help to reduce confusion...

Having 2 computers that you know are supposed to agree is good. Having 2 computers that operate exactly the same reduces the learning curve and task loading as you only have 1 user interface to deal with.

All of our computers are uwatec aladins and are extremely similar.

 

[uncfnp]

Just curious, when one dives with a back-up computer is it recommended that they be the same model (or brand)?

It depends on why you carry a backup. If its just to have in case the primary fails and you don't intend to use it during any given dive, use one with the same algorithm or more liberal. Then you can pretty much ignore it until needed.

 

[perry64]

It certainly is the easiest if your two computers match, it's the decompression algorithm rather than the model or brand. If they do not match, your dives will be controlled by the more conservative computer, either NDL or deco obligation. Many computers will lock you out for a period if you do not satisfy your deco obligation and you would lose the use of that computer. If you don't mind following the more conservative computer, then it makes no difference.

There was a saying back in the days when longitude could only be calculated by comparing local apparent noon to time on a ship's chronometer:

"Go to sea with one chronometer, or three chronometers, but never two."

I would say that the diving equivalent is, roughly, either use your more conservative computer as your primary, or completely ignore your more conservative until your primary computer goes down.

 

[kelemvor]

Just curious, when one dives with a back-up computer is it recommended that they be the same model (or brand)?

recommended yes. Required? no.

When I tried my hand at cave diving, I bought two petrel so that I'd have two which matched and had all the same everything. If I had not been able to afford them both, I would have used my scubapro Galileo in gauge mode as backup. I never worked out the details on how that would play out since I did buy two identical computers. If you're doing technical diving that requires a backup computer, you're probably spending bundles of cash on gear and training anyway... what's another $650 or so, right?

 

[scubadada]

...either use your more conservative computer as your primary, or completely ignore your more conservative until your primary computer goes down.

You will lose the use of the more conservative computer if you do not satisfy a deco obligation on it. That may be more likely if you use the more liberal computer and ignore the backup entirely. It could be unfortunate if your primary computer failed and you then discovered you were locked out of your backup.

 

[RayfromTX]

I use a perdix for my primary and a more conservative aqualung i300(basically free) as a back up. I blow it up early in the dive trips but it then goes into guage mode which is all I need to get me back to the boat if and when my perdix ever goes belly up on a dive. Arguably I don't even "need" that. I won't be buying another perdix as a back up but if a cheap deal happens on a backup with the same algorithm and GFs available, I'll drop the cash. I am referring to OW diving. What should I be considering that I'm not?