Tables & computers

[BDSC]

Realistically no one I know uses dive tables to dive. We all use computers for recreational diving. It's good to know how to use the tables and what the air groups means, but they're from Jacques Cousteau days.

I think I have seen one set of tables on a boat in the past 10 years and that was someone who was going through the DM classes and just wanted to stay sharp on them. For typical recreational diving, I don't see them being very useful.

 

[rhwestfall]

In 23 years of diving, I haven't had to replace my tables.... wish I could say that about computers....

The funny thing is that up here (Great Lakes), the dive profile is basically a square one so it is easily figured with a Wheel or the tables. There isn't really the big advantage here that reef/wall diving gains in computer use.

 

[fjpatrum]

Wow, it's been about 2 weeks since I asked the same question. So these things really do run in 2-week cycles after all. :goldfish:

I can't wait to try out my new computer. Counting down the days....

Interesting, the questions I saw from you were about dive planning and logging for computer dives, which isn't what I was referring to in this question. That said, the questions definitely go in cycles and I've been guilty of posting repeat questions before (and probably will be again...)

Is your computer air integrated and does it specifically say "NDL Time" or is it RBT for Remaining Bottom Time? I'm a bit of an air hog and my AI computer usually counts down RBT but it's based on air consumption and remaining air supply...unless I'm on my doubles or diving (too) deep I'm rarely capable of exceeding NDLs.

No, my computer shows NDL. I have zero interest or money for an AI computer.

 

[FPDocMatt]

Interesting, the questions I saw from you were about dive planning and logging for computer dives, which isn't what I was referring to in this question. That said, the questions definitely go in cycles and I've been guilty of posting repeat questions before (and probably will be again...)

Oh no, I wasn't criticizing, I was observing that the 2-week cycle that people keep referring to actually seems accurate. And you're right, your question and mine were different. I absolutely definitively am not one of those people who think people shouldn't repeat questions.

 

[drrich2]

Now, when I dive I use a dive computer. Before each dive, though, I check my NDL for my expected average depth against the tables and set a countdown timer for that # on a watch. When/if I hear the alarm on my countdown watch, I ascend, period. This is making me (perhaps) overly conservative if I'm spending a short portion of my dive deep and a long portion shallow, but it seems like a good method of ensuring I'm not pushing NDLs too badly.

Definitely over-conservative, and on what basis?

If I dove with you, I could set my countdown timer for half what the tables allow, and ascend no matter what. Then I'm supposedly 'safer' than you because I'm not pushing NDLs as much as you are. But a friend of mine might stay on the boat, and say he's safer than either of us.

I was mostly using the tables because they seem intuitive to me and it is an easy way to make sure I'm not doing anything stupid by blindly following the computer...

How is that different than 'blindly' following the tables? In either case, an inanimate object is giving you a guideline based on calculations most of us aren't familiar with made by people we don't know personally taking it on faith they're based in science (if only theory) and have stood the test of time well in actual practice.

It amazes me how 'graven in stone' some people take tables to be, yet how distrustful of computers some of the same people seem to be. You can ALWAYS dive 'more conservatively' and claim you're theoretically safer.

Some people dive nitrox using air tables. Some people cut their dives way short using tables.

Is there some actual morbidity/mortality data to guide this, or at least give people some idea of what risk difference is involved, or is this just a product of some people wanting to think they're 'extra' conservative/safe?

Over time, you'll sacrifice a lot of bottom time. I just want to know if there's a good reason to think you're getting anything real back for what you're giving up.

Richard.

 

[fjpatrum]

Definitely over-conservative, and on what basis?

If I dove with you, I could set my countdown timer for half what the tables allow, and ascend no matter what. Then I'm supposedly 'safer' than you because I'm not pushing NDLs as much as you are. But a friend of mine might stay on the boat, and say he's safer than either of us.



How is that different than 'blindly' following the tables? In either case, an inanimate object is giving you a guideline based on calculations most of us aren't familiar with made by people we don't know personally taking it on faith they're based in science (if only theory) and have stood the test of time well in actual practice.

It amazes me how 'graven in stone' some people take tables to be, yet how distrustful of computers some of the same people seem to be. You can ALWAYS dive 'more conservatively' and claim you're theoretically safer.

Some people dive nitrox using air tables. Some people cut their dives way short using tables.

Is there some actual morbidity/mortality data to guide this, or at least give people some idea of what risk difference is involved, or is this just a product of some people wanting to think they're 'extra' conservative/safe?

Over time, you'll sacrifice a lot of bottom time. I just want to know if there's a good reason to think you're getting anything real back for what you're giving up.

Richard.

Oh, make no mistake, I don't put "blind faith" in the tables. I put reasonable faith in the dive tables simply because they make sense and I can see the "brains" of how it works at different depths and the progression of things. As I said, it's quite intuitive for me. Similarly, it's not that I distrust the computers at all, it's more about being able to understand things without digging to learn what algorithm it uses etc etc. For example I've read both my computer's manuals multiple times and still haven't noted what algorithm either uses. (Both Oceanic so I'm pretty sure they use the same algorithm...)

I'm not necessarily deliberately trying to be more conservative but I didn't/don't want to do anything stupid by not having in my mind what SHOULD be reasonable (based upon tables) on a dive instead of blindly trusting a computer. I figure using one as a balance to the other isn't necessarily about being conservative but more about being prudent as a newb trying to learn what is really good for me as an individual instead of blindly trusting either one. As much as anything, for me, it's been about learning what is a reasonable display for my computer to be showing me just in case the computer goes haywire or something. It would be pretty horrible to dive for 100 minutes at 100 feet (not that I would be able to) just because I didn't know the computer was being stupid (no matter how unlikely that is).

Add to that the fact that I didn't really know how to "plan" a dive with my data plus. It's easier to plan dives on the Veo180 I'm using now so I suspect I'll be modifying my dive plans and actions accordingly. At this point I tend to be limited more by my gas consumption anyway, since most of my dives have been less than 40 feet depth.

 

[Paladin]

Realistically no one I know uses dive tables to dive. We all use computers for recreational diving. It's good to know how to use the tables and what the air groups means, but they're from Jacques Cousteau days.

Well, now you know someone who dives the tables. I have an Oceanic VEO 110 but I've only used it a few times and then it was in gauge mode.

 

[drrich2]

It would be pretty horrible to dive for 100 minutes at 100 feet (not that I would be able to) just because I didn't know the computer was being stupid (no matter how unlikely that is).

At this point I tend to be limited more by my gas consumption anyway, since most of my dives have been less than 40 feet depth.

I certified PADI OW back in '06, when tables were still routinely taught, and I keep a set for air & EAN 32 in my log book. Like you, I've looked at the tables to get a rough idea of how long I could stay down at a given depth on a single dive. Becomes more of a hassle with repetitive diving, which is also where NDLs are more an issue, since like you I'm more apt to be limited by air or nitrox supply on a single dive than by NDL.

I've dove several places but more of my dives were in Bonaire. Typical scenario is shore entry, swim out to reef, head down the reef to about 40 - 50 feet, then parallel to the reef maybe 20 minutes or to 1800 PSI or so, turn & come back shallower (maybe 20 - 40 feet), incorporate a safety stop and end the dive. BUT, I may make a brief 'detour' deeper to get a closer look at something - like dipping around 90 feet for a huge spiny lobster at 1,000 Steps, or close to 110 feet for a big hawksbill sea turtle. These detours to get closer photos of exceptional unplanned opportunities would cut a basic tables dive very short (assuming you're not using multi-level calculations), whereas on a dive computer it's not nearly as big an issue.

People love to say 'Plan your dive and dive your plan' (over and over and over...), and I agree on a rough basis, but I do some simple on-the-fly modifications (like dipping down to photograph those things) when I have good reason. Rarely do I rigidly adhere to a square dive profile.

As you get more dives in, you'll get some intuitive sense of about how long a tank will last you for a given dive plan you're used to (like my typical Bonaire shore dive). Not an excuse to get sloppy watching the SPG, of course!

Richard.

 

[Searcaigh]

Computer are probably the best tool for the job, which is why most divers use one. I prefer tables, mostly out of familiarity and simplicity.

-Mitch

And tables don't require batteries

 

[Mr Carcharodon]

At this point I tend to be limited more by my gas consumption anyway, since most of my dives have been less than 40 feet depth.

At 40 feet or less a dive computer is pretty much irrelevant since you will be close to or below limits. Tables might be a better choice. Of course you do need some way to track depth and time so you know for sure. Tracking average depth and time against NDL is a way to check that your dive computer is giving you reasonable answers. Not all of them do always.