Another Tables vs. Computers Thread

[Charlie99]

The computer may not force you up but will be telling to go there. For instance I had a computer that ran straight buhlmann. That's fine but I prefer buhlmann with gradient factors at 20/70 or sometimes 30/85 which results in stops starting deeper.

Obviously, a computer that is giving you limits based upon 100/100 buhlmann is going to be happy with a profile done with 20/70 or 30/85 gradient factor. As a side note, the green-to-yellow transition on the bargraph of my Oceanic Data Plus 2 computer is right around 80-85% of DSAT M-value, which pretty much also corresponds to an upper gradient factor of 80-85 on the ZHL16B or C models.

An exception?
....It was just a bottom timer and depth guage on that dive and it had no idea what gas I was diving ..... I was lounging around at 30 ft and the decompression obligation was climbing through the roof. ..... After I was out of the water I found out that the computer had been set to "hard dive conditions". I don't know much about what that does aside from further limiting bottom time. I'll let you tell me why the decompression obligation should still be going up when I was at 20 ft?

Let's see now ... 1. It wasn't set to the gas you were using. 2. You had cranked up the conservatism to some unknown level. Yep. An excellent example of how not to use computers.

Most dive computers crank in conservatism in essentially the same way that gradient factors do in deco planning programs -- by reducing the M-values. To a casual observer, it looks like it is a reduction in bottom times, but what really is being reduced is allowable compartment loading limits.

It may simply be that the allowable limits of the slower compartments had been reduced so drastically by you conservatism setting that you had exceeded the limits on the slower compartments. Reduce the M-values / gradient factor enough, and you will be increasing your deco obligation at 30'. I have a hard time figuring out how conservatism could be cranked up so far as to still be adding to deco time at 20'.

In any case, whether due to operator setup errors, or bogus operation of the computer, you did as a good diver should do, and applied some sanity and reasonability checks to what your instruments were telling you.

 

[H2Andy]

 

[minnesota01r6]

Andy, how many threads are you gonna post that in?

 

[H2Andy]

my goal was 13,456 but i got bored

 

[bennedc]

my goal was 13,456 but i got bored

Now that I know what a troll is (thanks, Andy), can we get that smiley changed to trolls beating each other with clubs instead of little yellow blobs? It would be so much more meaningful...

 

[Rick Murchison]

It is truly amazing how many times people think that you have only an "either-or" choice. As in, I must bring EITHER the axe OR the chainsaw, when there isn't any reason that you can't bring both, and some DEET too.

And maybe even use both computers, tables, mental tracking, and a large dose of seat-of-the-pants flying.

I second the motion...
Rick

 

[Scubaguy62]

Quoted from another thread:

Ignoring issues of reliability, just considering understanding of decompression, why do so many people repeatedly say that learning to use the deco tables in OW is preferable to learning to use a computer?

If this has been mentioned, excuse me for repeating; I chose not to read all responses.

When you know the why about something, the how comes easy. Say you can memorize the NDL times at 3 or 4 depths, idealy the ones you most often dive; does it not make it easier to set up your computer before the dive, rather than arbitrarily setting a dive time which might be beyond the NDL and just sit there waiting for the alarm to tell you when it's time to ascend?

If you do that, you're doing the infamous "trust me dive," only you're trusting your computer. In the event of a failure, assuming you're using a stop watch or a timer of some sort, along with the computer, you just might be able to make a safer ascent and deco stop.

I use my computer as a back up to my tables, not the other way around. But, as someone else mentioned before, it's likely to be due to my pilot and flight instructor training.

 

[Blackwood]

Learning tables, especially if you really study them can leave you with enough in your head that you pretty much know what the computer is going to say before it says it.

While I agree (as my post in the other thread asserts), I must ask this in keeping with the thread topic.


If it is preferable to learn tables before learning computers because knowledge of tables enables one to make judgement calls in trusting computers, what should divers learn before the tables that will enable them to make judgement calls in trusting the tables?

In other words, where does this slippery slope end? Drawing a unit fluid cell and deriving a theory of gas decompression? If so, then diving is an activity for only the most brilliant mathematicians. If not, then at SOME point, one must trust something that someone else came up with, be it a computer or a deco table*. What, qualitatively, makes a table worthy of blind trust than a computer (again with the caveat that we aren't considering equipment failure)?


*In fact, even deriving a deco theory requires trust in something else, including but not limited to: establish math paradigms, laws of physics, etc..

 

[Charlie99]

I use my computer as a back up to my tables, not the other way around.

I notice you are in Boca Raton. If I lived there I probably wouldn't bother with a dive computer, since the dives on the 3rd reef are generally pretty close to square profile. (That's also why nitrox is really popular there, but that's another subject). OTOH, when diving places like Maui or Cozumel, which lend themselves to very nice multilevel diving, then using square profile tables is unduly restrictive.

Even as a hoovering novice, my dives in Maui were way beyond square profile table limits, leaving me with the choice of cutting dives short or using a computer. Only after doing many dives did I start getting a good feel for what combinations of depths and times are good multilevel dives.

Initial OW cert classes don't teach any effective techniques for planning multilevel dives other than the rather awkward PADI Wheel. IMNSHO, that's a big gap in dive training.

 

[Blackwood]

For those who think this thread is getting off topic, I have split the thread again. It can be found here

d'oh

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