SanDiegoSidemount
Contributor
Depends on what fails, though. Right?
If the only thing that fails is tank pressure you're probably OK with an analog SPG as backup, but if the computer battery dies, even having a backup depth gauge probably means you're not diving your plan as a minimum. Did you check your NDL on the RDP before diving, or did you expect the computer to be there until the end of the dive?
My analog backups would be there to help me abort the dive safely. If it's the first dive of the day I'd need help calculating a safe second dive on an RDP if the first wasn't planned that way - bottom time & depth, etc. Even if you fix your computer it probably isn't reliable for planning the next dive since it wasn't there for the first.
Or not, tell me where I'm wrong.
You're not wrong at all, however, different people use computers in different ways. How you use the computer will dictate how screwed you are when it fails.
If you rely on your computer to give you on-the-fly NDL and track your N2 loading across repetitive dives, then you are totally dependent upon it. You'd better carry a second computer if you don't want to take a 12 hour break after a failure, or have a buddy who's diving all the same profiles with you.
On any dive, computer or not, nobody should enter the water without knowing their NDL for the planned depth. So with backup depth/time (yours or your buddy's) you should be able to finish the dive safely, without much urgency. In this case, it would be your choice whether to thumb the dive at the failure or finish as planned. (Of course, how many divers omit this basic pre-dive check?)
What happens after a computer failure depends on how you manage your repetitive dives. I personally use min deco, so my computer is just there to give me depth and time. (And gas pressure if I'm using my rig with the AI sender.) So I could carry on using the normal min deco repetitive calculations.
If you rely on your computer for repetitive dive profiles and have no backup computer, maybe you could reconstruct your repetitive dives with tables and info from your buddies? Seems pretty iffy to me. If you really care about your health, you'll want to sit out for 12 hours.
This issue (as well as the OP's original question) comes back to understanding the consequences and fall-backs if a critical piece of gear fails, and the risks (or inconveniences) you are willing to accept. Some divers don't think through failure points much, and accept more risk. I'm probably guilty of over-thinking failures, and being more risk-averse the older I get.
I think we can all agree we want to come back alive from our dives. Beyond that, it's a matter of personal preference.
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