backup computer

[rhwestfall]

as the saying goes, "Stupid should hurt."

 

[steinbil]

So let's say you are doing a multi-level dive (for the sake of argument, on air). Your maximum depth was 91 feet, but you were there only about 8 minutes before beginning a multi-level ascent. You are at 36 feet when your computer fails after 36 minutes of dive time.

Tell me what you do next, both on that dive and the dive coming up after a 60 minute surface interval.

If you keep track of average depth, this is actually quite simple. On any ascending multi-level profile (starting at max depth and gradually diving shallower) it's not problematic to use the average depth with tables.

Let's say the average depth was 65ft, round it up to 70ft. 36 minutes at 70ft gives you letter R on the PADI RDP. Continue diving tables this way. If you think this is not safe, I challenge you to simulate any similar profile, and you will see that it is MORE conservative than a square profile to 70ft for 36 minutes, in other words similar or lower risk.

 

[ofg-1]

Don't those backup computers make an annoying beeping noise?

 

[boulderjohn]

If you keep track of average depth, this is actually quite simple. On any ascending multi-level profile (starting at max depth and gradually diving shallower) it's not problematic to use the average depth with tables.

Let's say the average depth was 65ft, round it up to 70ft. 36 minutes at 70ft gives you letter R on the PADI RDP. Continue diving tables this way. If you think this is not safe, I challenge you to simulate any similar profile, and you will see that it is MORE conservative than a square profile to 70ft for 36 minutes, in other words similar or lower risk.

You are at depth when your computer fails. Where do you find your average depth?

 

[rhwestfall]

next discussion:

the 120 rule...



For some reason, the older I get, the less I'm interested in "risks"...

 

[steinbil]

You are at depth when your computer fails. Where do you find your average depth?

True, this will be the limiting factor for most divers. But some divers are actually trained to do this, so for the divers used to keeping a running track of average depth it is possible. For most divers, they would need at the very least a backup bottom timer that would keep track of the average depth.

 

[rhwestfall]

For most divers, they would need at the very least a backup bottom timer that would keep track of the average depth.

And, with the really low cost of many modern PDC options, why bother?

 

[Centrals]

In my experience when diving with 2 or more computers which give different results, the most conservative computer, when in deco, clears upon ascent without a need for a stop.

It won't be any Cressi, Mares and Suunto using RGBM.

 

[Centrals]

And, with the really low cost of many modern PDC options, why bother?

Indeed.
SP 300m bottom timer is more expensive than some basic computers. Battery changing is not even an option.

 

[boulderjohn]

True, this will be the limiting factor for most divers. But some divers are actually trained to do this, so for the divers used to keeping a running track of average depth it is possible. For most divers, they would need at the very least a backup bottom timer that would keep track of the average depth.

Yeah. I was trained to do this myself, as were my dive buddies in our UTD training group, including the ones who got bent after a dive in which their math on that calculation (and other parts of the dive) was not all that it should be. Call me crazy, but when I am on a NDL dive, I prefer to focus my attention on what I am seeing during the dive rather than doing a constant mathematical calculation of my average depth so that I will be prepared in case my computer goes bad (which has never happened).

Or you could buy a bottom timer for the price of a cheap computer. Just remember that the battery is not replaceable, so you will have to throw it away when it dies. When mine died, I never replaced it.