Back Up PDC - holder only?

[Damselfish]

The failure points are something like this. In essence they are all user errors or conflicting info errors.
1: you set the wrong mix or don't set it at all, rendering the deco info useless
2. The deco profiles don't match, which one do you believe?
3. It's battery dies because its a secondary piece of gear, and you need it
4. It's another piece of gear that can be lost.

Me I carry a watch computer, tables in my wet notes and a bt that I actually
compute deco with based on a written dive plan in my wet notes from deco planner or vplanner. My buddy carries a computer and backup bt with depth.

I'm not saying backup comps are bad or anything but in reality my computer is my backup to the run schedule plan. I do not fly the computer.

A back up computer I feel is most useful in your bag in case of the primaries failure you switch to for your next dive and splash.

Well, when you asked why someone might want a backup computer, you didn't specify tech diving, so everyone has assumed recerational no deco diving in their answers and I think that's quite clear. (Maybe that's what you expected, just so you could disagree?) For rec diving the things you suggest as failure modes, aren't. If my computer has reset to 21% O2 and I haven't caught it - big deal - the next dive is a little more conservative. (Computers vary in their behavior in this and you should of course know what your computers do.) The profiles don't match? - you go with the more conservative one, duh. If the battery dies or you lose it - well that is the reason to have a backup, not a failure mode of the backup.

A computer in your bag is not a backup computer. It's a spare bottom timer/logger.


But the OP didn't ask this anyway, they were simply looking for a place to put it.

 

[JahJahwarrior]

The failure points are something like this. In essence they are all user errors or conflicting info errors.
1: you set the wrong mix or don't set it at all, rendering the deco info useless
2. The deco profiles don't match, which one do you believe?
3. It's battery dies because its a secondary piece of gear, and you need it
4. It's another piece of gear that can be lost.

Me I carry a watch computer, tables in my wet notes and a bt that I actually
compute deco with based on a written dive plan in my wet notes from deco planner or vplanner. My buddy carries a computer and backup bt with depth.

I'm not saying backup comps are bad or anything but in reality my computer is my backup to the run schedule plan. I do not fly the computer.

A back up computer I feel is most useful in your bag in case of the primaries failure you switch to for your next dive and splash.

On a recent dive for instance I accidentally triggered the gas switch to my 50% deco bottle at 85 feet, violating the mod AND the dive plan the comp was tracking for both deco and CNS. I at no time switched gasses but the comp plan was toast. My runtime schedule was fine for the dive so I carried on, after switching it back to the correct gas I followed the runtime schedule for the slight deco obligation and had a good dive.
A backup computer would have allowed the same thing but why not default to the lower tech solution that does not rely on electronics?

Failure points...it's a tricky subject, because all gear can fail. Typically, it fails because of a failure point, that's why we call them faily points. But, failure points don't have to be related. For example, a first stage HP seat blow out will cause a "failure" of the second stage as it freeflows. However, a failure of my backup computer doesn't cause a failure of my primary computer, nor of my deco plan, as I have a third backup which I calculate will keep me from getting bent. The fact that a secondary piece of gear can fail does not, and should not, preclude one from carrying a backup.

Carrying a backup computer in your dive bag defeats the purpose. Since it won't know your saturation, it will give you much longer NDL's when you do start to use it, which will lead to you getting bent. Once all of the computers you have been diving with are dead, your only option is to manually calculate your saturation using tables and the records of your dives that you better have been writing down for the preceding dives, then continue diving using tables.

 

[rlynch]

Ok, here our rec profiles for ndl are a bit more on the edge, due to a square dive profile and the depths but my point is that a backup is something you rely on, namely your tables and a buddy. Your buddy should be close and therefore on the same plan and profile and you have discussed it prior to the dive.
If you need to compute multi dive saturation use vplanner or tables. My point is that relying on a computer for all your diving is bad juju.
I keep a backup in my bag in case my main comp dies. Which is my answer to the op. Have a way to compute depth and time as a back up, and know your plan.

I think the delta is in the philosophy rather than anything else.

A computer does not eliminate the need for a plan and a back up means of figuring out ndl or deco if needed. Which IMHO should be as simple as possible. You need to default to simpler options as the stress/task loading increases.

These are not tech profiles that I am talking about either. We also do gas planning as part of the predive sequence which is another topic.

 

[Damselfish]

whatever. You dive in a way that works for you, I'll dive in a way that works for me. I'm certainly not telling you how to dive, maybe you shouldn't think your way is the only right one or best for everyone else.

I will add that you are making another assumption - that all dives are done with the same buddy. Sometimes I am on vacation with a group of friends, and we may switch around depending on who feels like diving or whatever, or even in the course of a dive. So again, I can't assume my buddy's current profile is applicable to me even if we're currently glued together.

Out now, as this has all been done to death a zillion times. Hopefully the OP finds something to hold their backup computer.

 

[rlynch]

Nope you do it your way. deep sea supply makes nice wrist mounts for most comps. I don't always have the same buddy but we stay within a couple of fin kicks regardless. Otherwise your solo.

 

[GaryDZ]

Thanks for all the responses. I ended up buying the Oceanic B.U.D.

 

[dmoore19]

I think you made a good choice. I have a BUD for a backup. My primary is also an Oceanic computer so the 2 pretty much agree with each other all the time.

 

[mbs]

Hmmm, I'm sure Oceanic thinks you made the right choice But for me I think you were on the right path initially. Unless you were having trouble with your original computer! I took my wife's old oceanic veo 180 as a backup and got a hose mount boot from Oceanic. The 180 pops right in it and I clip it to the hp hose my primary is on. Can't find the part on the Oceanic site anymore... Used it several times already. Once the hp hose blew and I couldn't get it replaced on the trip. So I borrowed a spg and just took my backup and clipped it to it... No loss of repetitive profile AND when I got home I could still upload all my dives to my pc.

 

[dmoore19]

Hmmm, I'm sure Oceanic thinks you made the right choice But for me I think you were on the right path initially. Unless you were having trouble with your original computer! I took my wife's old oceanic veo 180 as a backup and got a hose mount boot from Oceanic. The 180 pops right in it and I clip it to the hp hose my primary is on. Can't find the part on the Oceanic site anymore... Used it several times already. Once the hp hose blew and I couldn't get it replaced on the trip. So I borrowed a spg and just took my backup and clipped it to it... No loss of repetitive profile AND when I got home I could still upload all my dives to my pc.

I also throw a SPG w/hose in the bag. I also wear a dive watch with a bezel for time and it also reads depth. Computer failure #1, end dive, surface, install SPG. Computer failure #2, (unlikely but possible) begin using watch for depth and start using ERDP for planning dives, I could also use my iPhone app for planning if I needed to.(a copy of the tables is also in my log book) Yes, I have thought out a contingency process to eliminate the need to miss dives while on a trip. If the watch and the iPhone app and the ERDP all fail then I guess I will have to sit out 24 hours. Did I mention I like watches and have 2 suitable for diving? I have a retractor mount SK7. If that fails I will need to follow someone else for navigation. I do like my toys!

 

[doctormike]

Thanks for all the responses. I ended up buying the Oceanic B.U.D.

Seems like the thread got a little off track from your original question!

If it's not too late to return the BUD, you could save yourself a good deal of money by using your old computer. Assuming that it's a real hockey puck and that you don't have any sort of boot that you can MacGyver into a holder for it, you can get one of these for $18 from Deep Sea Supply, get a bolt snap for about $5, and put a couple of zip ties between them, to make your own BUD.

The BUD has the advantage of being pretty small, so if that's worth the extra $225 to you, just keep it.