Karl_in_Calif
Banned
PhilD once bubbled...
A question regarding the use of a backup timer, do you do a pre-dive plan and work out your BT for the planned depth, so in the event of a computer failure you could continue the dive, or would you abort the dive if the computer failed and just use the backup timer to confirm the computer?
My computer is a nitrox computer. I normally dive air on my first dive, and nitrox on all subsequent dives. I keep the computer on nitrox mode and dial in 21% for the air.
I use the backup timer to 1) verify that my readouts on the dive computer are functioning correctly and 2) in case the dive computer fails, so that I can abort this dive with the benefit of the digital depth read-out. Remember, 30 ft per second is one-thousand-one one-thousand-two for every foot during ascent.
I do not believe it is totally safe to dive without 2 electronic devices. Some people define that as your computer and your buddy's computer. That however fits my definition of buddy dependent, and I do not believe in doing that either.
My first stop is always 1/2 of my max depth on the dive, and then 10 ft every minute afterwards, with remaining gas at 20 ft. To do all that properly during a bail-out requires a backup electronic device.
If you are out of the country on a dive vacation, and your primary dive computer fails, then you could use your backup timer for use with tables. So I do bring tables along with me. An air table, and an EAN36 table. If the mix is not EAN36 then I will compute the EAD and use the air table. Then I would have to live with being buddy dependent in terms of redundancy, but figuring in the thousands of dollars I had spent on the vacation, buddy dependence then becomes a valid risk.
Otherwise it would be possible to go to the dive store and get the computer fixed right away after aborting the dive. I know a great store owner, who does all the gear maintenance in his shop by himself. He is good. I would simply beg him to fix it for me right away, and pay him generously to drop everything else.
He also knows I am getting ready to buy a drysuit for my fiance', and he knows I will order it from his store. So he does not mind dropping everything else.
Pre dive planning for fun dives normally consists of lets go that way, turn around at 1/2 PSIG, and spend as long as we can at 20 ft on the way back.
The tank size and SPG is always by default the primary planning device on the first dive. The nitrox mix normally accomplishes the same thing on the second dive. The dive computer just keeps you honest. Sure you can do it all in your head, on the fly so to speak, but I dive to relax, not to run math equations in my head.
One electronic device is certainly the norm. But then, I never held a very high opinion of any norm, anywhere.