Must I abort if computer fails?

[TMHeimer]

So if your computer dies on the first dive you're OK to continue with tables by just checking what your max depth was. If it dies on subsequent dives you could continue if you had previously planned square table profiles for the entire day. Most divers probably wouldn't have done that, assuming the computer won't die. If you have kept track of all pressure groups while the computer was working you could still switch to tables at any point--is this correct?

 

[victor]

Here's one backup theory that I have heard of that seems quite logical.

Works best with Pelagic computers or others that use the DSAT algorithm, and PADI/DSAT tables.

Upon surfacing from each dive, immediately run the DC through a diveplan mode and note NDL for 100 feet. Use this NDL to find an equivalent pressure group from the tables. It is now theoretically possible to pick up tables from that point.

I think this would work, you would then be able to incorporate your next dive using the surface interval and max depth.
The problem that is most likely to occur is that if your dive computer craps out more than 50% through and you have been on a multi level dive, you next calculation is going to put you in deco on the tables. Thus you are out of the water for 24 hours anyway as you missed your deco stops.

My watch gives me max depth and time of my last dive. I have tried to use the tables after a dive day and I was so into deco after the 3rd dive, where as on the computer I only pushed the amber a couple of times. This was reef diving, deepest at the start (60 ft) work gradually up to the dropoff (30ft) on 100 bar and swim back along the drop off until 50 bar exit.

I have never tried doing this with the wheel, probably on these dives I could get a reasonable result, but I am not sure how safe it would be.

 

[boulderjohn]

If your computer craps out during a dive, you don't have to worry about any incompatibility between your computer's concept of the residual nitrogen in your system, and the tables. In fact, you don't need the tables to compute a square profile that takes into account your previous dives.

All you have to do is go into the plan mode of your computer just before your dive and punch in your planned maximum depth. The computer will tell you your maximum time at that depth with a square profile, taking into account your previous dives and your surface interval. If you can remember that number, you can complete the dive on backup gauges if you lose the computer during the dive.

 

[DA Aquamaster]

Many divers (the smart ones) would suggest planning the dive, then using the computer only after you have a general idea of the site, max depth and expected bottom time (due to either gas limits or deco limits). That certainly works on the first dive with a level bottom and dive profile. It works well too on the first dive with a multilevel profile using either a multi level dive planner like the Wheel, with regular tables using multilevel procedures, or with software such as DPlan on a Palm device.

For other than the first dive of the day, you'd figure your dive profile based on what you actually did (simple notes of depths and times on a slate will suffice) and detemrine your repetitive group with tables, or enter the actual profile into software like Dplanner where you'd then also enter the SI and the next dive plan.

One thing to consider though, is that if the computer fails, you need backups for depth and time, so a bottom timer is important to have to back up the computer, and if the computer is an inexpensive hockey puck design, a back up conmputer is only going to be another $100-$150 more than the bottom timer.

 

[highdesert]

Since my wife/buddy and I have both had computer failures, I argue for full redundancy. We both dive an AI computer on a hose, we both have a wrist mount backup computer, I have a watch on the other wrist, and we both have an SPG. When our diving comes many months apart and involves long, expensive plane rides to exotic places, and no LDS down the street, we want to know nothing is going to impede our dives.

 

[Colliam7]

I'm wondering...if you have redundant gauges, would it not be of benefit to have made a square profile "worst case" dive plan from the tables before the dive? ...Is it really always necessary to abort

No, it is not - unless you are using your computer for gas supply information, with no back-up. If you have gauges, if you have already planned your NDL dive using tables (and including previous dive information as Lynne mentioned), there is no reason to abort.

 

[rstofer]

If your computer craps out during a dive, you don't have to worry about any incompatibility between your computer's concept of the residual nitrogen in your system, and the tables. In fact, you don't need the tables to compute a square profile that takes into account your previous dives.

All you have to do is go into the plan mode of your computer just before your dive and punch in your planned maximum depth. The computer will tell you your maximum time at that depth with a square profile, taking into account your previous dives and your surface interval. If you can remember that number, you can complete the dive on backup gauges if you lose the computer during the dive.

But there are those two requirements: First, the NDLs for all likely depths has to be written on a slate (unless the bottom is ABSOLUTELY known) and, second, the diver needs backup gauges (max depth and time).

Even so, this only resolves THIS dive. Future dives are probably out of the question without GUESSING that the NDLs written above could be translated into a table pressure group. This is not a chance I would take. The day is over...

FWIW, I seriously question that "note the 100' NDL" approach. Fast cells versus slow cells versus a serious lack of knowledge re: deco theory leaves me in the "I'm not doing it!" camp.

The solution is a redundant computer. Not a buddy's computer, their profiles may not match (we already discussed computer sharing) but an actual second computer that has been on every dive.

In the end, it's just a dive! Abort the thing, don't take any risk of DCS and use the redundant computer for the rest of the day. Lacking a redundant computer, wait for another day.

I can hear it now! "But this trip was EXPENSIVE!". So? Buy a redundant computer. They're cheap compared to a trip.

Richard

 

[dumpsterDiver]

If your computer craps out during a dive, you don't have to worry about any incompatibility between your computer's concept of the residual nitrogen in your system, and the tables. In fact, you don't need the tables to compute a square profile that takes into account your previous dives.

All you have to do is go into the plan mode of your computer just before your dive and punch in your planned maximum depth. The computer will tell you your maximum time at that depth with a square profile, taking into account your previous dives and your surface interval. If you can remember that number, you can complete the dive on backup gauges if you lose the computer during the dive.

That is very true, I never look at tables, but I do usually have a decent idea of my planned depth and I take a look at the computer so i have an idea of the NDL for each dive. This is the most rudimentary of dive planning. In addition, it might allow you to realize that the computer is not working correctly if it gives you wacko numbers before the dive or unrealistic numbers when below.

The big problem with continuing a dive after the computer craps out is that you have to know the elaspsed time and I almost never set my dive watch to record the start of the dive, although it would be good practice. However, for planned deco dives,
I usually try to remeber to look at the watch right before jumping in.

The answer to the question at hand is, don't do anything stupid. If you are at a depth that you know is not going to be a problem, then keep diving! If you have no clue, then you had better head up ASAP. Of course you coudl rely on your buddy's computer if you are willing to bet a lot of marbles that their compter is reprentative of your profile.

If all this stuff is not intuitively obvious, then yeah, you better head up immediately if/when the computer dies.

 

[SCUBASailor]

I don't see a problem with this either, assuming you still had some way to determine your depth and bottom time. Unfortunately, most computer "failures" I'd expect would crap out one or both of these functions.

I am assuming that one is diving with a watch and depth gauge in addition to the computer. I am diving tables for now until i get my computer. It seems prudent to continue carrying the depth gauge and watch even after I buy my computer.

 

[Gombessa]

I am assuming that one is diving with a watch and depth gauge in addition to the computer. I am diving tables for now until i get my computer. It seems prudent to continue carrying the depth gauge and watch even after I buy my computer.

I do repetitive dives with depth gauge and spare wristwatch and don't own a computer. The tables work quite well for multiple-dive days too, we've cleared 10 dives over 2 days including 90-100ft (on 32%), verified through deco software. I think of you know your tables and profiles and play it safe with common sense, you'll be fine. Best of luck.