Dive computer question..

[herman]

I usually dive 2 computers on Bonaire, the main set to nitrox and a backup set to air. I mainly do it because my old air comp was in my console and my new comp is a wrist mount so why not leave them there. If you intend to depend on both, dive both on all dives so both can keep up with you dive profiles. Depending on how you dive you may not really have any reason to worry about comp failure, the best diving on Bonair is 40 ft or less so it's hard to come close to NDL's even with the tables. For what it's worth, I have never seen my air comp get close to any NDL much less the one set for nitrox. We dive 3 to 5 times a day with an average dive time of 60 minutes, 75 min is common and I have done as long as 90 minutes.

 

[Damselfish]

When I got my first Nitrox computer I used it in Nitrox mode but kept the air computer with me as a backup. While I wouldn't be anywhere near the edge of the Nitrox computer I would be pushing the air computer as I wouldn't normally (not really of course, it just thought so.) Very occasionally the air computer would get a few minutes into deco and I hung out to make it happy. Not as good as a Nitrox backup but I did it for a few trips and it was an ok compromise.

 

[DavidInNH]

I think that using a Nitrox computer on Air mode is more conservative but then again, maybe too much so. After all, you're potentially limiting your bottom time so that the benefit of Nitrox is lost. (Aside from confusing your dive buddy when the air computer starts beeping for no apparent reason!)

My suggestions in order, are as follows:

1) Spring for a new backup computer that does Nitrox.
2) Borrow someone else's backup. (Now, if you were in a dive club, you might know someone who could lend you one.)

 

[Quarrior]

I see all these ideas, including my previous comments. Bottom line in reality is the age old, "any time a primary piece of equipment quits, the dive is over."

What this means is if your computer dies, you get with your buddy and thumb the dive.

 

[Damselfish]

I see all these ideas, including my previous comments. Bottom line in reality is the age old, "any time a primary piece of equipment quits, the dive is over."

What this means is if your computer dies, you get with your buddy and thumb the dive.

Well, the whole point of a backup computer is to avoid that. You could say at that point the backup has become the primary, if you like.

 

[Quarrior]

Well, the whole point of a backup computer is to avoid that. You could say at that point the backup has become the primary, if you like.

Wrong.

Once you go to a backup, you end the dive. Whether it is a backup light or anything else, the dive is over.

 

[Charlie99]

What this means is if your computer dies, you get with your buddy and thumb the dive.

For me a dive computer failure would NOT automatically cause me to abort the dive. Instead I'd apply some common sense.

My computer keeps pretty good track of depth and time, but I also pay attention and pretty much know what it should be reading. Failure of the dive computer might cause me to abort a few dives, but on most I'd just go ahead and finish it off normally.

One should always have a mental picture of your decompression status. There are lots of shallow dives where a dive computer is optional. Lots of times I have done a particular dive, or combination of dives, before and know roughly what depth I need to be at different times and/or SPG readings.

If it's a solo dive, usually it is shallow enough that decompression is not a signficant issue. For other dives, there are one or more computer which I can compare against my mental image of my current decompression status -- taking into account possible difference in profiles.

Even if, for some strange reason, I didn't have a good idea of my decompression status I'm not going to exceed 10 minutes of required deco when diving an AL80. So in the worst case, I just include 10 minutes of hang (for which I only need 250psi) at the end of my ascent.

 

[Quarrior]

Charlie,

Are we giving advice to someone that has as much experience as you or even I do, or someone that has minimal experience?

My advice is based on the latter. There are a lot of things the more experienced diver does and can do that the diver with a low amount of experience should not do.

 

[Damselfish]

Wrong.

Once you go to a backup, you end the dive. Whether it is a backup light or anything else, the dive is over.

That may make sense in some situations, like where the backup gear is considered critical to begin with. But I'm talking rec diving where the norm is to have 1 computer. If one computer fails, I've still got one. Saying it's ok to dive with one computer if you start that way, but not if it happens during the dive, is illogical.

The same would apply to a light. I'm sure in a cave, if your main light fails it's time to head out. On a rec dive, if my main light fails I'm down to one light - which is all that most people are carrying to begin with. The risks are just not that high.

 

[Markdone]

Setting your computer to 21% will provide you with a much better safety margin, but in Bonaire, I am sure you will find it the limiting portion of your diving. Also, you need to be more aware not to exceed your MOD since your computer won't be monitoring it for you.

Please don't forget to track your O2 loading. If you're going to set your comfuzer to 21%, you'll need to track your daily O2 limits by hand, not just your MOD.