Another Tables vs. Computers Thread

[Scubakevdm]

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'm with you Charlie, at least for regular diving. Dives requiring multiple gas switches are a little bit different, but as you noted earlier, I still rely on a computer prior to the dive, and still eyeball the plan and measure it against a ballpark table plan. It's kind of a silly arguement that's going on.

 

[Diveral]

computer reliability DOES NOT EQUAL safety. If your computer or bottom timer fails, you thumb the dive and make a conservative safety stop. A competent diver in either situation would recognize the failure before exceeding NDL limits. An incompetent diver in either situation is in trouble.

That would really bite like those Canadian Mosquitoes if, say it were halfway through the first dive at the Flower Garden Banks. If you were cognizant of your dive tables and NDL's and had a back-up bottom timer and depth gauge it would result in no more than an inconvenience.

 

[DivesWithTurtles]

Tables use a shorter compartment time for the so-called "controlling" compartment on repetitive dives - most computers use much longer compartments for this. For example, US Navy tables used the 120 minute compartment, where as DSAT (i.e. PADI) tables use the 60 minute compartment. Dive computers will typically use their longest compartment - perhaps something in the 480 to 720 minute range. The longer the half-time on the controlling compartment, the less bottom time you get on a repetitive dive - the effect of this is that tables generally give you more bottom time on flat profiles, whereas computers generally give you more time on multi-level profiles.

Your analysis is in error.

While the dive computers track all of the compartments, including the very long half time compartments, after a typical recreational dive, the very long halftime compartments have relatively little loading and have no effect on the next dive.

If your analysis were correct, then decompression programs such as Decoplanner and V-Planner, since they also track the very long halftime compartments, would give you less time on flat bottom profiles than tables. You can easily verify that this is not true. Nor is your original assertion.

DIR-A, Charlie is (as always) right on target here. The 60 minute compartment for the DSAT and the 120 minute compartment for the Navy tables are used to calculate Surface Interval credit, not repetitive dives. Computers continue to track all of their compartments during the surface interval the same way all of the compartments are tracked during dive time. The controlling compartment is the most heavily loaded at any given time. Tables only consider all of their compartments during dive time.

Thank you for correcting blueeyes_austin's misunderstanding regarding algebra and calculus. blueeyes_austin's statement just supports my (and TS&M's) original premise that learning to use the tables or learning to use computers doesn't equate to understanding how any of those numbers were derived.

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Between speedhound, minnesota, ReefHound and rottielover, this really is a thread for the dogs, huh?

 

[Scubakevdm]

Hi Gabe! How's things?

 

[MikeFerrara]

Rather thasn spending 11 useless minutes, you and your buddy should learn how to use your tools properly. Too bad you and your buddy weren't able to catch the error during your buddy check.

Do you have any example where a properly used computer has forced anyone to dive a profile other than what you desired?

A lot of people have parroted the "doesn't give credit for deep stops" line, but if you actually look at what happens, you will find that the computer does indeed properly account for offgassing in the faster compartments.

You, at least, have not parroted the false logic about a dive computer forcing you to immediately pop up to the ceiling depth that will be shown when in deco.

As far as I know a computer is going to calculate all applicable compartments so, it is going to give you credit for going shallower even if you do not ascend the the cieling that it displays (assuming that you've gone into decompression). 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.

An exception?
I did use one computer as a bottom timmer once that did appear to penalize me although I say that not knowing the details about the model it was using. It was my second dive of the day and it was about an hour dive to a max depth of 65 ft with an average of about 50 ft. On my way back, (I was in a cave) the computer went into decompression and was telling me I had 1...2..5....9 minutes at 10 ft. It was just a bottom timmer and depth guage on that dive and it had no idea what gas I was diving but I had fun watching it. I was lounging around at 30 ft and the decompression obligation was climbing through the roof. By the time I was at 20 ft the displayed cieling was finally down to 15 or 17 ft and up to a displayed total ascent time of about a half hour. 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? You don't suppose that I was really in the water long enough to load those slow compartments do you? The thing certainly did appear to add decompression as long as I was below it's displayed cieling. The good thing about that computer is that it wouldn't ever lock up which is why I could use it for a bottom timmer.

 

[DivesWithTurtles]

Hi Gabe! How's things?

Good, Kev. Good to see your face and tongue here. I think I'll call down there tomorrow morning and book for this weekend. I'll be the one with a computer. Or tables. Or both. Or seat-of-my-wetsuit. I don't know. They're all good.

 

[Scubakevdm]

Good, Kev. Good to see your face and tongue here. I think I'll call down there tomorrow morning and book for this weekend. I'll be the one with a computer. Or tables. Or both. Or seat-of-my-wetsuit. I don't know. They're all good.

Awesome. You rule man.

 

[BHB ScubaTroll]

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

 

[The Chairman]

Tables are a true stumbling point for quite a few divers. They can understand the concepts, but equating a letter group to how much N2 is in you can be problematical and is anything but intuitive.

I have also noticed the DEARTH of tables on dive boats, and most divers are content to do "trust me" dives on schedules dictated by the captain. So, if they are going to toss tables to the side once they get through the class: why stinking bother? Tables are like snorkels: they usually stay in your bag or at home and very, very few divers take them seriously.

I see teaching how to dive a computer and then making sure the student understands that they are certified to dive in no other way as a way around this phenomenon. Students will trust their computer, and most need no input from the user as they are started by immersion should they forget.

On top of this, the bubbles used by most computers to graphically show N2 absorption is quite intuitive for the student to comprehend. They can see the bubbles GROW and they can see them decrease. This is indeed a GOOD thing and unlike the tables letter group, it is quite intuitive. Easy and convenient are not synonyms for death and stupidity.

I do predict that tables will go the way of the "Navy Seal" style training of the 60s and 70s. In reality, they already HAVE, but many instructors are stuck with a failed schema for teaching how to reduce the risk of DCS.

As for the comments about (the horrors) missing a day of diving. It seems that few are willing to call a dive or a group of dives. The ocean will still be there tomorrow... or next year. The earth will not stop and there are probably PLENTY of things to do topside, should you find yourself like a fish out of water. Hey, we'll let you come on ScubaBoard and post in the Whine and Cheese forum to get it off of your chest.

 

[bennedc]

Table? Isn't that a thing you eat off of? I have NEVER used a dive table, ever, other than in the class. ANCIENT HISTORY...I think I saw a documentary on the History Channel about dive tables, or wait....was that National Geographic? Hummm