Question Backup dive computer

[Divin'Papaw]

I had an issue with my Aqualung I770r the other day between dives for some unknown reason it froze up saving the dive profile 10 minutes into the SI. I didn't have a backup computer but did the second dive on gauges loaned to me from the dive operation ( used 45 min bottom time @ 80 ft 35% nitrox table to do it). I didn't go on the afternoon dives I had scheduled that day because of the issue even though the dive op offered to rent me a computer. I just felt that it was better to call the day than to keep diving without the complete mornings profile on the computer I would have rented. That said I want to get a backup computer just incase this happens ever again. What I am wanting opinions on is should I get one with the same algorithms for NDL or not really worry about that part? I don't intend to get an AI model as I have a backup SPG already. I would setup the backup and take on the dives with me but only to use it to continue a day's diving should the primary ever lockup again.

Good call IMO.

 

[TrimixToo]

I run two Shearwaters set to different levels of conservatism (using different GFs). I dive using the more conservative settings. The other is the "if the SHTF" one, to get me out of the water as quickly as possible consistent with what I percieve as reasonable risk.

 

[Stoo]

I bent my (then) back-up which was in my pocket while my main computer worked through the dive....

Try to find something that is running a similar algorithm....

This. Having matching pair is really nice, and much less confusing. Two different algorithms can give remarkably different results, especially when you're doing actual deco dives. You end up staring at the two of them and trying to figure out which one is right, when they both are.

Having said that, I used to use those TUSA pucks of various brands. Even though they were the same, the profiles were often quite different.

I now use two Shearwaters on bigger dives. They're within seconds of each other. (Although I kinda like @TrimixToo 's approach!

 

[TrimixToo]

<snip>

I now use two Shearwaters on bigger dives. They're within seconds of each other. (Although I kinda like @TrimixToo 's approach!

I cannot claim credit for the idea, which came from a friend. But I found his logic pretty compelling.

 

[Stoo]

I cannot claim credit for the idea, which came from a friend. But I found his logic pretty compelling.

I'm all for borrowing the brains from others. Being an older guy, I dive what are likely overly conservative profiles. Having a "hasty exit" plan in the box for that time things go sideways is rather clever.

 

[Divin'Papaw]

I run two Shearwaters set to different levels of conservatism (using different GFs). I dive using the more conservative settings. The other is the "if the SHTF" one, to get me out of the water as quickly as possible consistent with what I percieve as reasonable risk.

For a technical/decompression diver, this approach makes sense. However, it doesn’t provide any benefit for a recreational NDL diver. Regardless of what my computer says, I can ascend straight to the surface at 30 fpm in an emergency. It won’t bend either computer and I’m on the surface as quickly as is safely possible.

 

[Stoo]

For a technical/decompression diver, this approach makes sense. However, it doesn’t provide any benefit for a recreational NDL diver. Regardless of what my computer says, I can ascend straight to the surface at 30 fpm in an emergency.

That being the case, you really don't need a backup, as long as you end the dive if you're computer bites it. Mind you, if you're on vacation when it dies, having your spare all charged up with your residual nitrogen.

 

[Tracy]

I'm all for borrowing the brains from others. Being an older guy, I dive what are likely overly conservative profiles. Having a "hasty exit" plan in the box for that time things go sideways is rather clever.

With newer firmware, you can display your live GF on the main screen, running a separate algorithm is rather pointless as you can see exactly where you currently are at any point during the dive. Once it drops into double digits, you are "technically" clear should you need to ascend at that point.
On dives that have gone pear shaped when I needed to be on the boat deck immediately, I have ridden 99 to 20' and then waited til the number I wanted to see appeared. It is sometimes known as ascending on your ceiling.

 

[Divin'Papaw]

That being the case, you really don't need a backup, as long as you end the dive if you're computer bites it. Mind you, if you're on vacation when it dies, having your spare all charged up with your residual nitrogen.

There is more than one reason to dive two computers. I have a backup to be able to continue diving that day/weekend, not to get me safely to the surface.

 

[Stoo]

There is more than one reason to dive two computers. I have a backup to be able to continue diving that day/weekend, not to get me safely to the surface.

Indeed... hence my comment about having the backup with you so it's tracking residual nitrogen.