Genesis once bubbled...
Can opened... what does it say on the side? 
WARNING! Lol...
In all seriousness, how big of a deal is it if the computer pukes on you? You know where you were when you last looked it at.
That's an excellent point, and certainly some of the reasons for the huge difference in opinons between divers about computers. The truth is that there's two very different possible answers to your question.
The first one has the results exactly as you mention. If you're doing a no-deco dive on air, for example, then your 'puter can tell you, with some reasonable amount of accuracy (according to unproven mathematical theories), when it's time to get out of the water, lest you risk having to decompress. (Which isn't as scary as it sounds... It's nothing more than a planned "safety stop" or two.) If the computer craps out on you, then you're not too bad off... You look at it, and you remember that a few minutes ago you still had eight minutes of bottom time, for example. Now your computer's dead, so it's time to abort the dive. What do you lose? Well, maybe a few minutes, but nothing real serious.
With that in mind, check out the dive tables that PADI publishes. I'm not going to go into it too far (I'll let you use your brain on this one so that what I say doesn't fall on half-informed ears), but notice something interesting... There is a rule of 120. Basically, add your bottom time to your depth, and never exceed 120. If you want to go to 60 feet, don't stay down for more than 60 minutes. If you want to go to 80 feet, don't stay down for more than 40 minutes. If you want to go to 100 feet, don't stay down for more than 20 minutes. Get it? The two numbers max at 120. Of course, this is a bit conservative for shallow depths, and only applies to the FIRST DIVE OF THE DAY. Subsequent dives have different formulas, but just as easy to figure.
Now, there's a couple of things that you need to know about that formula... That rule can apply to the diver that's relatively fit, and in good general health (not hungover or strung out or obese), and assumes an ascent rate of 30 fpm, not 60 fpm. Also, GUE's teaching how to judge a general average of depth, not max depth like PADI teaches. However, they're making other assumptions that make up for the difference, like the 30 fpm thing.
Get it? It's a very easy, broad way to work your general tables underwater and in your head... But before using it, it assumes some things about the diver. Thus, it's not published information.
It also does not take the place of dive planning on a table or computer in the first place. Please don't take this as gospel... Simply put, this and other great gems of knowlege were given to us at DIR class, and I wanted to use this as an example of why DIR divers don't bother with a computer.
Okay, the first possible scenario is the diver doing some no-deco diving. The second is the diver doing a deco dive.
Imagine the diver going say, to 190 fsw, and diving for 22 minutes. He looks at his computer, and it says he's 18 minutes into the dive. Three minutes later he's thinking that he's ready to end the dive, and he wants to know where and how long to do his stops... When suddenly, he realizes that his computer is dead. What does he do then?? If the diver was reliant on that computer, then guess what... He's screwed. He'd better know a little about deco!
Furthermore, there's more complex issues, too... What if there's multiple breathing gasses involved? What about Trimix? DIR teaches that Nitrox, if possible, should be used when diving at depths of 100' or less. Anything deeper really should be dived on Trimx, so as to help offset narcosis problems. And simply put, I don't know of a reliable He computer.
So "what's the big deal?" Well, it really depends on your situation. However, DIR training always works in all situations... The computer solution isn't always going to work in every dive situation. Thus, DIR teaches that computers are better left topside.
So you abort there, and do your backup plan. The one you figured out before you got in the water. If you don't know how much deco obligation you have, you extrapolate. If you have a buddy, he has a computer (or timer and tables), and while you won't be exactly right, that's ok - you pad it and go off that.
Agreed. That's not the best solution (knowlege and understanding, IMHO, would be better than "padding your buddy's numbers"), but it should probably work either way. Again, there are some computers that I like... So you aren't telling me anything new... I'm simply trying to explain their position, and I can completely see the logic. Doesn't it make more sense to save the money and instead gain the true understanding?
The DIR guys I know, by the way, DO dive with computers... They dive with them in "guage mode." That means that they can see depth and time counts, and of course, they can make judgements on their air supply. They also have the advantage of being able to download their profiles later onto a computer. The only difference is that they don't generally trust the computer to tell them when to abort the dive. They make the decision themselves.
Put bluntly, I was told that "The right computer will tell me everything I need to know, without telling me what to do." FAir enough. You gotta understand, these guys are doing literally THOUSANDS of dives a year. Believe me, if there was a better way, they'd be diving it.
If I lose my computer I ascend on my buddy's. If it calls for deco, we do it according to his profile, and pad the stops a bit to account for the fact that I may not be "exactly" the same as him in terms of my profile.
No different, really.
Yeah, agreed there, too. There is a little difference, but it's not much... But I think we agree that this little difference is huge when it's put into application.
I once saw a diver getting out of the water at Ginnie Springs. They were equipped quite well, with drysuits, doubles, and thousands of dollars' worth of gear. When I saw a Cochran computer on one of their wrists, I jokingly yelled out to my sweetheart, "It's okay, honey... This one's wearing a computer... They're not DIR!" (I said this as a joke, as if DIR divers were something to run from... And of course, as if these divers were not DIR because they were wearing a computer. I offended them right away... They were both "very DIR" and did not hesitate to tell me so. Apparently, the Cochran had been in "guage mode" during the dive.)
If I'm going to do a planned deco dive, then I have to have bailout contingency tables somewhere (in my head or on my person) because the water may turn brown on me. But I need those regardless, and using something as a backup isn't the same as using something as a primary resource.
Agreed.
It sounds remarkably like you and DIR do agree on a lot... Just slightly different approaches on it. They teach that computers aren't necessarily bad, but when people have them, they tend to rely on them wholeheartedly... And that can be bad, especially if the dive turns into a deco dive.
I'll give you a real-world example. If I dive tables around here, for Nitrox let's say I dive a 30% mix on a 110' spearfishing dive (the cut mix to keep the PO2 under 1.4) By the tables I have an EAD of 100' (if I'm rounding as the tables require), and a NDL of 20 minutes.
But, in truth, I can stay down there for an extra 5-10 minutes if I do the dive on a computer, since I won't be at 110' the entire time, and the computer doesn't have to round off either the expore or the EAD. My runtime can be significantly longer than 20 minutes in this case, perhaps as much as 50% longer (30 minutes), without going into decompression!
Yes, I'm aware. DIR teaches a "law of averages" that works similarly. I agree that this is a better way to dive.
Another interesting tidbit is the fact that most computers are using bubble models that are based on a "worst case scenario" example. They must assume that you are a coffee-addicted, overweight, smoking desk-jockey office person who dives twice a year when they make that computer "safe for most users." If that doesn't describe you, then a more aggressive dive profile might be more applicable to you. And you will be thrilled to know that in many cases, combining the "law of averages" with a more appropriate and more aggressive dive profile can lead to even LONGER dive times.
In that scenario, you'd really begin to hate your computer, and simply switch to guage mode...
In fact the difference is even bigger than it appears, since there is time consumed from getting in the water until you reach the bottom; sometimes more than others, but it does count.
Agreed. And the real question is, at what depth does offgassing begin to occur? There's lots of theories on it... But what they're teaching at GUE (and deco is not something that I've been taught by them yet), is that deco stops should begin much deeper than the traditional theories teach. It's an interesting perspective; unfortunately, I am not educated enough about it to discuss it. All I know is that they do support the idea of deeper deco stops.
If it takes you 2 minutes to get down from the surface (when the clock starts ticking) then that's 10% of your "bottom time" off the tables! So now its even GREATER than a 50% improvement in REAL bottom time.
Agreed. And the real question is, "When does your body begin to offgas? At what point do you begin to deco, and count that time as reducing your deco obligation, rather than adding to it? Agreed that computers have some theories about this... Which is why computer failure for a deco diver can be so tragic, and why many deco divers do not trust computers.
I often do dives in a day that the tables say "can't be done", because I blow the charts (and I DO check on a multi-dive day, just in case I have to "back into" the tables after a computer failure) yet I do them safely and have LOTS of remaining NDL time on the computer. Why? Because the computer can accurately account for the ACTUAL profile, while no set of tables can REASONABLY do that, except for certain very specific situations. Now if I have a computer fail on me when the backed-up computation says I can't continue then I remain out of the water for the day - that much I am forced to accept. But if it happens on the FIRST dive of the day, I can still go - just recompute on the tables and dive them from that point forward.
Well, if you take five different computers with you on your dive, you'll get five different answers as to what you can and can't do... Which is really scary that they're all disagreeing about what's safe. As you well know, your tables tell you something entirely different, but you've provided a believable explanation for this.
...So what's the answer? Well... It depends on which one of them you believe. Scary, hunh? With some reasonable understanding, it's safe to say that the most conservative dive profile will be the safest. However, there's no question that this is probably a bit
too conservative, and so you have to make your decisions as to who or what to believe.
The DIR way of doing multiple dives involves a simple theory like the no-deco theory I mentioned above. I would share it, but I don't yet know it. Certainly it would not be as conservative as the tables, yet it would not be as aggressive as the most aggressive profile in the most aggressive computer on the market. But it would be judged without the reliance on the microchip, that's for sure. At least, not complete reliance.
Don't get me wrong... I like the idea of computers, for all of the same reasons you mention above. Most instructors and LDS's teach reliance on the computer, with little prior planning. DIR teaches the opposite. Who do we believe? Well, that's up to you. Who do I believe? I don't see, really, how the two theories are conflicting. I think both theories are excellent, and I think there is room to agree with both schools of thought.
I see no downside to the computer. And air integration puts everything in one place, and with FAR greater accuracy than an analog SPG will ever have.
I agree on a couple of points you make... I like the idea of keeping all of my guages in one place. However, that does have a downside. When your buddy is out of air, it's practiced that you should supply them air, situate them, situate yourself, and then check your guages and make a decision as to whether or not to abort the dive immediately (as you would in most boat dives) or to swim to the upline or out of the cave first, then surface (as you might have to do in an overhead environment.) Either way, it's practiced that once you make the decision, you should check your air supply (so as to make the best decision) and then communicate your decision and your air supply with your buddy. Nothing helps add to the confusion of an OOA quite like a computer display with all kinds of numbers on it, or showing him a console with two or three guages. What he really needs is one bit of information... How much air is available. Nine times out of ten, there's no shortage of it (because you've planned so well), and it at least relaxes them, seeing that you've got plenty of air to sustain both of you. So what do you need to show them? One very simple and very accurate guage... Not a confusing mess of numbers that only makes anxieties increase. Do you dive the same computer as your buddy? Do you think they could read your computer in a near-panic situation? SPG's work really well for this.
There's also the idea of teaching the diver to be reliant on the computer, which happens eventually, to computer divers. It's not necessarily a good thing.
Lastly, for deco divers, most will tell you that deco's best done with no reliance on any piece of gear that can fail... Including a computer.
And what about SPG's? Well... They've proven to be more reliable than hoseless, wrist computers that are dependent on two batteries and a software engineer somewhere.
Again, it may not look like it, but I like computers... I'm simply trying to explain their theories on the use of computers... So that their perspective doesn't seem so "whacked." Personally, I understand their position and support it... Although I also think computers are cool.
I'm not willing to give up the 50% bottom time extension for "religious purity"
It's got nothing to do with "religious purity." DIR divers don't care about "religious purity." What they care about is the safest, most accurate, and most reliable way to dive. And their theories and beliefs are different from yours.
Me? I can see both sides of the coin, and I think I want a Vytec. When I have a spare $1200 sitting around, I'll probably get one. Of course, I don't think I'm going to sacrifice my SPG, though.
