Exploring some back-up / redundancy options thoughts?

[DiverGuam]

If you have two computers running different algorithms, they will disagree on what they're telling you to do, so which one will you follow? One won't be backing up the other in case of a failure, because they're running two different programs in the first place.

Since either is an approximation, isn't it better to have two different approximations using two different theoretical frameworks? If either fails you have no choice which to follow, but if neither fails and they are running the same algorithm, you are leaving yourself short of info that you would have if you had two computers running two different algorithms.

Two different frameworks leads to no choice only if one dies. The same framework on to different computers leads to no choice if neither dies.

To Tortuga's point, I have had two computers fail on a dive. I was wearing three at the time (all running different algorithms).

 

[Tortuga68]

Tortuga. While I appreciate your thoughts, I have never suggested triple redundancy in any of my posts on this subject. I am trying to remain rational and reasonable, not ridiculous.

I didn't say you suggested getting three computers, just illustrating my point. You got it, which is that more redundancy is not necessarily better. There is a point at which it's not justified.

Commerical planes have triple redundancy because they carry hundreds of passengers and the consequences could be dire.

At what point additonal redundancy is unwarranted depends on the individual. For me, two computers, AI and/or an SPG is not warranted for the type of diving that you are doing, given the low probability of failures and the mild inconvenience of cutting a dive short if they do.

You asked for thoughts on your plans, mine are that 1 computer without AI and an SPG are more than adequate. That's what I use on recreational dives, sometimes just a watch and SPG, or even SPG only. YMMV.

 

[decompression]

Min deco works very well and doesn't require batteries or a place on your wrist. Also cheaper than a computer.


Sent from my iPhone using Tapatalk

 

[Tortuga68]

Well to be fair minimun deco requires something to measure time & depth...

 

[decompression]

Not a computer...... But yes.


Sent from my iPhone using Tapatalk

 

[Blyslv]

After reading through this and some other computer thread, I'm kind of confused! Just one narrow question for now.

I do not understand why two different algorithms is a bad thing if you are looking for redundancy. Both computers would (or should) be working with essentially the same inputs: maximum depth, time at that depth, dive profile, total elapsed time, and previous surface intervals; (and there are probably other inputs for rec diving that I may have missed).

Presumably the outputs should be the same for all computers (with some variations depending on whether the programming for the algorithm is "conservative" or not). These outputs being NDL or not, recommended safety stop, required surface interval, no fly time and others that I am sure I am missing.

If the outputs are wildly different between two computers using different algorithms, wouldn't that say that one is somehow mistaken? Should the outputs be within a relatively small range of each other because they are starting with the same basic inputs?

In any event, for a beginner rec diver, the thought of buying two computers is rather daunting to the wallet. However, I was told that the analog SPGs on the regualtor/hose setup where I learned to dive did not work. So as newbies we relied on the DM. That is not a viable option going forward, as I am learning that a DM cannot always be present, and I want to develop my own skills.

So. Why not an excellent computer, with an excellent analog SPG (preferably in both feet and meters), and if the unthinkable occurs and both fail, ascending slowly, no faster than the smallest bubbles, and stopping occasionally and counting off three minutes or so? This assumes a dive of no greater than 30 meters/~100ft. As a rec diver, I do not want to go deeper than that until I have a lot more experience.

 

[flots am]

I do not understand why two different algorithms is a bad thing if you are looking for redundancy. Both computers would (or should) be working with essentially the same inputs: maximum depth, time at that depth, dive profile, total elapsed time, and previous surface intervals; (and there are probably other inputs for rec diving that I may have missed).

A man with two watches never knows what time it is.

In any case an open water diver doesn't actually need redundant computers. The procedure for an equipment failure is to ascend with the buddy and end the dive.

flots.

 

[kr2y5]

A man with two watches never knows what time it is.

A man with 2 eyes cannot see anything, a man with 2 legs cannot go anywhere...

In case of a computer failure, even a recreational diver would still want to maintain an optimal ascent rate, hold the safety stop at a proper depth, and have some protection for those rare, but not impossible situations when the diver might accidentally incur a small deco obligation during a recreational dive, and where it would be really helpful to have access to decompression information.

One reason I can think of for having identical computers would be, to make sure that one is familiar enough with the backup to operate it after the primary fails, but is this really an issue in practice? In theory, I would think that having different computers gives a marginally lower risk that they will exhibit the same kind of failure at the same time, since they are unlikely to suffer from the same software or hardware defect.

 

[flots am]

A man with 2 eyes cannot see anything, a man with 2 legs cannot go anywhere...

In case of a computer failure, even a recreational diver would still want to maintain an optimal ascent rate, hold the safety stop at a proper depth, and have some protection for those rare, but not impossible situations when the diver might accidentally incur a small deco obligation during a recreational dive, and where it would be really helpful to have access to decompression information.

Recreational divers are not supposed to have decompression obligations, and are supposed to surface with their buddy in case of equipment failure.

What you have is an equipment solution to a problem that only exists in divers that ignore training. If you're going down that road, you can pretty much do as you wish.

flots

 

[DiverGuam]

In any event, for a beginner rec diver, the thought of buying two computers is rather daunting to the wallet. However, I was told that the analog SPGs on the regualtor/hose setup where I learned to dive did not work. So as newbies we relied on the DM. That is not a viable option going forward, as I am learning that a DM cannot always be present, and I want to develop my own skills.

That's not what was happening. I can hazard some guesses as what was actually happening, but.

I do not understand why two different algorithms is a bad thing if you are looking for redundancy. Both computers would (or should) be working with essentially the same inputs: maximum depth, time at that depth, dive profile, total elapsed time, and previous surface intervals; (and there are probably other inputs for rec diving that I may have missed).

Presumably the outputs should be the same for all computers

If the outputs are wildly different between two computers using different algorithms, wouldn't that say that one is somehow mistaken? Should the outputs be within a relatively small range of each other because they are starting with the same basic inputs?

There is no way to answer completely in this basic forum, but suffice it to say this: Those assumptions are incorrect. Because it is expected that algorithms can and will generate significantly different NDLs on a given set of repetitive no-stop dives. That fact is the reason to carry computer of different algorithms. To carry only one algorithm is to lose info, even if one has a redundant computer.

On a side note, no one knows how fast they are ascending without a computer or an electronic depth gauge. Once someone commits to taking electronics underwater (watch, electronic depth gauge), then they have committed to depending on electronics underwater, and deciding against a using a computer instead of another electronic device is being willfully obtuse.