Computer backed up by analog and dive tables?

[ozziworld]

I was wondering how one would continue diving after a series of dives with a computer and and then resume the next dive after the computer conks out (for whatever reason). Assuming the first series of dives were all within the computers limits I have always found the dives always exceed the dive tables.

How then, assuming you log the first series of dives using the computer do you continues the series using dive table?

Hypothetically, let's say this were to happen on a liveaboard in the middle of the trip?

Is the only way to sit out a day's diving then just simply resume using tables?

Basically, how do you do the dive profiles and determine your repetitive group letter accurately if after the computer conks out all you may have logged are max depth and bottom time? Is this the reason why hardcore tech divers dive stictly tables?

I ask this question because I was wondering how much I really need the bottom timer and depth guage in terms of continuing a series of dives versus just finishing the last dive the computer may have failed to complete.

Am I right to assume the best thing to do is just stay out of the water for 24 hours before resuming diving?

Any advise would be much appreciated as I am beginning to feel that I should back up my computer with another computer and not just analog and dive tables.

 

[Charlie99]

Staying out of the water for 24 hours is obviously a safe method.

If none of my recent dives were beyond NDL, my dead computer backup plan is simply to assume that I surfaced from my last dive as pressure group Z on the PADI RDP and plan my dives using that table. Since I wasn't in deco, then I'm within limits on all compartments of the deco model, including the 60 minute compartment used for repetitive groups on the RDP.

I would start wearing my backup computer at that point, but would use the tables to set my bottom time until after an overnight break. At that point, I would start using my computer to plan dives.

You should use all of the available information to check the validity of your intended dive plan --- that includes things like what your buddy's computer says (taking into account your relative depths on previous profiles).

Extending your safety stop will add additional safety margin.

 

[Doc Harry]

Charlie99,
That's what I do, too.

 

[stairman]

Thats a good question.If you and your buddy were together the whole dive I would go with his info.Too bad computers dont list a pressure group number.Then you could finish tracking with an RDP.I dive ttwo computers so the chance of both crapping out is slim.This scenario does make you think though.

 

[ozziworld]

Thanks for the replies, seems we are in agreement that the best thing is to stop diving for 24 hours before resuming diving on the event of computer failure. Doesn't avoid the lost dive opportunities though.

I think the best way then would be to dive two computers so that one is the back up to the other. That way both computers a reading same dive profile exactly and backs up the other in case of failure.

Now what to do with the analog depth gauge and bottom timer? Having just the SPG at the end of the HP hose sounds very tempting at this point. Any thoughts?

 

[Pearldiver07]

I wear a Scubapro Xtender (wrist watch style dive computer). I use another one with a larger display during diving, but this serves as back up during trips. The watch style stays out of the way and provides a nice back up.

I've had a computer death during a trip, I hate losing a day.

I really dislike using a buddy's profile - 10 feet differences during a dive can really vary your numbers if you're diving aggressively. Of course, if you're spending most of your time on top of a 40 FSW reef, it'd work great.

 

[Doc]

If you and your buddy were together the whole dive I would go with his info.

anicbutton:

Is the only way to sit out a day's diving then just simply resume using tables?

:rtfm::bang::deal: Close, but no. Go rent another computer after 24 hours.

 

[Gilldiver]

I you were not into any DECO you can do as one poster suggested, assume that you were at max NDL for the next depth deeper then you know you were, say 90 feet if you were at 80. Now enter the tables at that level and go for it.

If you were into DECO you should have a very good idea of where you are in the table sand be following a dive plan.

By the way, I have seen computer flood, run out of battery and get lost on dives, you should have some back up plan for such - no one seems to mention wrist mount computers getting lost - with a secondary timer and depth gage.

 

[Charlie99]

I you were not into any DECO you can do as one poster suggested, assume that you were at max NDL for the next depth deeper then you know you were, say 90 feet if you were at 80. Now enter the tables at that level and go for it.

That is NOT a valid way of moving over to tables. Using this logic, then assuming you were at max NDL at 130' would be even more conservative. A quick look at any table will tell you this is not true. For example, on the PADI RDP when you hit NDL at 130', you are only in pressure group H. This is because dives deeper than 40' are limited by compartments that are faster than the 60 minute compartment used to define repetitive groups on the PADI RDP.

What I do know if I have stayed within limits of the deco model is that all compartments are within limits, including the compartment used for repetitive dive groups --- 60 minute for PADI RDP; the 120 minute for USN table and those derived from it such as NAUI, YMCA, SSI. With the PADI RDP, having the 60 minute compartment within limits means that I have not exceeded the highest pressure group, Z.

This is true independent of the depths of previous dives, and whether or not they were multilevel dives. This is particularly important to me since many of my dives in Maui are extremely multi-level dive while still staying within NDL on the computer. For example, a common first dive for me is 100' maximum depth, 1 hour dive time (using an AL80). This is waaaaay off the square profile tables, so the common suggestion of manually keeping track of pressure groups doesn't work for me.

 

[HowardE]

What are the profiles for these hypothetical dives? Would you be diving to the NDL's on every dive? Are you diving Air or Nitrox?

IMO 24 hours is a bit conservative... especially if I were on a liveaboard. I wouldn't want to sit out a day because of a computer malfunction.

I'm sure (depending on the profiles) dived, that a safe "resume" point on the tables could be calculated.