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rfreddo
08-14-2007, 09:49
Can anyone point me to a post that explains, in newbie terms, the pros and cons and components of each? I'm sure it's out there, but I can't find it with the search feature.

ScubaToys Larry
08-14-2007, 10:05
Real easy... here you go. A dive computer - in the good ole' days, by definition is simply a depth gauge that has your dive tables loaded in it. So at any given point during the dive it knows how deep you are, how long you have been at different depths as you've gone up and down, and it crunches those numbers into it's computer and lets you know how much longer you can stay before you have to go up so you don't get the bends.

It simply displays your allowable time at that depth in minutes. So for example, maybe you've been diving for a bit and you are at 80 feet. You look at the computer - it says depth 80 ft, time - 4 minutes. That means you have 4 minutes there - not 4 minutes to get to the top. So now you go up a little shallower, head up to say 60 feet, and now it says you have 12 minutes left. That is all based on your nitrogen loading and your NDL (no decompression limit).

So the problem is you may look at that and see 12 minutes left - but maybe you are down to only 200 pounds of air left! Obviously you will not last 12 minutes on 200 lbs of air! You should already be on the boat!

So in steps the AI computer. (Air integrated). It is looking not only at your NDL, but also your breathing rate at the depth you are at, and how fast are you going through your tank of air. Then it does calculations to tell you how long you have based on your air consumption before you have to go up. And it does this with a "buffer" that you set. For example, you can say you want to hit the surface with 500 psi. The computer looks at your breathing rate and gives you a number - let's say 5. That means you have 5 minutes of "air time" left before you have to start your ascent so you will still hit the surface with 500 psi.

It is constantly updating based on depth and changes in your breathing rate, so it may show 10 minutes, but then you start breathing harder because you are swimming into a current and it drops down to 6.

The Oceanic / Aeris computers run their displays so the number you will run out of first - either your NDL time or your Air time is the number displayed, and it gives you a little icon next to it to let you know what the limiting factor is.

For example, you are at 80 feet, but down to 2000 psi. The computer shows 6 and a little icon of a dive profile. This means you have 6 minutes of no-deco time. You push the button on the computer, and the display changes over to how much "air time" you have - 9. Since the 6 is less than the 9, it pops back in about 5 seconds to again show you the limiting factor.

So you slowly head up the reef and come up to 40 feet. Now you look at the computer, you are at 900 psi, and the computer shows 7 with an icon of a scuba tank. That means you have 7 minutes before you have to go up based on the amount of air you are using. If you push the button, it swaps to the No-Deco time you have - but since you are shallow, that is now 41. Then again, it swaps back to your limiting factor - in this case the remaining air.

So really, diving with an air integrated computer is pretty easy. Jump in the water and don't let the big number hit zero! That's it. If that number starts getting small... start going shallower, and you will get more remaining time, based on either your air or nitrogen.

Hope that helps!

Oh.. the Pros - tracks everything for you and stops you from making mental mistakes, has alarms you can set for remaining air, turn around air times etc. The only Con... costs more.

It's really just like the computer in your car. You could just look at a gas gauge, or the computer read out that says, based on your current speed and driving conditions, you have 132 miles until empty.

Zenagirl
08-14-2007, 10:33
One more pro: All of your information is in one place. With a non-AI computer you have to check your computer and your pressure guage both.

If you go AI on a hose, get a quick disconnect so you can remove it from your regs for cleaning, storage, etc.

rfreddo
08-14-2007, 15:07
Larry -

It looks like many of the dive computers are able to interface with a PC. I'm sure there are a million reasons this is a good thing, but does it also give you the ability to "tell" the computer which dive table to use (e.g NAUI vs. PADI) or do they use their own, proprietary tables? Which brings up another couple of questions. Not having looked at anything other than my NAUI tables, I assume, but don't know for certain, that there is minimal difference between the various recreational tables. Is that a fair assumption? Is there a rule of thumb for buddy diving where the buddies typically rely on different tables? Something like "use the most conservative table?"

thesmoothdome
08-14-2007, 15:17
Yes, many of the computers allow PC interface, but you cannot change the algorithim that the maker has chosen. If you're diving with someone who is using a more conservative computer than you, then yes, you'll be limited to the algorithim that is on the more conservative computer.

BSea
08-14-2007, 15:22
Larry -

It looks like many of the dive computers are able to interface with a PC. I'm sure there are a million reasons this is a good thing, but does it also give you the ability to "tell" the computer which dive table to use (e.g NAUI vs. PADI) or do they use their own, proprietary tables? Which brings up another couple of questions. Not having looked at anything other than my NAUI tables, I assume, but don't know for certain, that there is minimal difference between the various recreational tables. Is that a fair assumption? Is there a rule of thumb for buddy diving where the buddies typically rely on different tables? Something like "use the most conservative table?"

The rules are the same for computer dives as they are for dives using tables. Any diver can end the dive whe he/she feels the situation dictates. So if it's a computer that is close to NDL, or just getting low on gas, the diver ends the dive for both partners. So if 1 is diving a more conservative computer, then that diver will usually decide when the dive should end with all other things being equal.

cgvmer
08-14-2007, 15:48
Larry that was helpful, Thanks!

GordoninNM
08-16-2007, 00:14
This question comes up a LOT, and Larry's post and the follow ups cover most of the bases in simple terms understandable to even the newest of divers.

Gordo

ScaredSilly
08-16-2007, 13:38
Lets not forgot one other major part. Reliability. Have seen several computers go tits up because of the pressure transducers. Turned mine on one time and it read 4000 psi. And that was not a "cave" fill. Couple of other times read low by 400-500psi on two others. In all cases the computer was replaced free of charge but the reliability of the transducers is less than a good brass and glass SPG.

That said I still use them. But realize their limitations and plan accordingly.

THT98
08-16-2007, 23:34
I have a couple of integrated computers (one on a hose and the other hoseless), and I really like them both. The reamining bottom time calculation is really helpful because it helps you understand what 1700 PSI really means at a certain depth. As Larry discussed above, you do have to be aware of your NDL time as well, as you could easliy slip into Deco if your breathing is good. They are a great investment, and I think you would be glad you went with air integrated.

ScaredSilly
08-17-2007, 12:50
The reamining bottom time calculation is really helpful ...

I am the opposite. This is the one thing that I find to be less than helpful. I totally ignore it. But I can see how some like it.

DarkCoffee
08-17-2007, 13:48
As a lake diver I find the RBT helpful in two ways:

1) since current is not an issue of significance, it does provide a ball park RBT provided my profile stays the same on the way back;

2) if it drops suddenly its a good clue that I'm breathing too hard and its time to reassess what I'm doing. I find that 'hint' darn useful as it's physical 'feedback' rather than a subjective thing of 'how do I feel?'. Of course that assumes Its not a change in my dive profile thats causing the RBT change.

dogseatmayo
08-05-2008, 19:43
wow larry. i bet you could publish that post and make it into a 200 page book! :)