Computer diving

[RLarsen]

Please explain how computers help you have longer dives. Also, I've heard that some dive charters insist on computers. I just returned from my first big dive trip to Cozumel and we all had high-end computers. The DMs gave us our minimum PSI and when we reached it we started heading toward our safety stops. Computers didn't have any impact on the length our 2-tank, am dives.
Rex

 

[The Kraken]

Hi, Rex !!!

A very basic answer to your question is that a computer allows the diver to do a "multi-level" dive without having to do the proper pre-dive planning and preparation.

Insted of diving a "square profile" that is generated by using the RDP tables, the computer takes periodic samples and computes your nitrogen loading based on the time you've spent at specific depths.

 

[Buoyant1]

To expand...if your maximum depth is 60 feet, but you only spend say 1-2 minutes there, and the rest of your dive is at 45 feet, you would naturally use 60 feet as the max depth you use on the RDP, severely limiting your bottom time, and putting you into a higher pressure group. The computer takes advantage of what depth you are, and as The Kraken posted computes your nitrogen load based upon the time at the given depth.

For someone like me who isn't quite getting the miximum time out of a tank yet, I won't benefit from getting the max bottom time...but someone more experienced, in better shape, etc. who COULD get more than say 60-75 minutes on a tank it would be a benefit because they could stay down longer...

With that in mind...a lot of people are leery of using them because it could put you into a false sense of security by replying on the computer and it could get you into trouble. Most people suggest using both. One person I dove with in July (who has more bottom time than I do suface time) spot checks his with his RDP about every 5 dives.


One thought though...using a computer that someone just handed me 5 minutes before the dive, I think I would definately consult my tables afterwards...

Hi, Rex !!!

A very basic answer to your question is that a computer allows the diver to do a "multi-level" dive without having to do the proper pre-dive planning and preparation.

Insted of diving a "square profile" that is generated by using the RDP tables, the computer takes periodic samples and computes your nitrogen loading based on the time you've spent at specific depths.

 

[shugar]

to add even more to that...

a computer generally also takes into consideration your nitrogen loading from multiple and consecutive dives (over a couple of days let's say)... this you can also do with your RDP but to take off from kraken and the bouyant1, you'll be computing these from a very black-and-white square profile that won't actually give you an accurate assesment of your actual nitrogen load...

if your DMs are going to tell you to thumb the dive at a certain PSI then you won't "feel" the effect of your computer, but do this over several dives for instance (let's say a liveaboard) and you might actually have to thumb your own dive when your computer tells you you're due for a shallower depth or SI rather than waiting for your SPG to hit 500psi

i can't wait to get my computer (WEDNESDAY!!!!)

Jag

 

[kevink]

With that in mind...a lot of people are leery of using them because it could put you into a false sense of security by replying on the computer and it could get you into trouble. Most people suggest using both. One person I dove with in July (who has more bottom time than I do suface time) spot checks his with his RDP about every 5 dives.

One thought though...using a computer that someone just handed me 5 minutes before the dive, I think I would definately consult my tables afterwards...

On a multi-level dive you won't be able to 'spot check' against an RDP. If I run a 60 minute dive with a max depth of 80' (average depth of ~45) my computer chugs this profile out no-problem. Find this on ANY RDP for me. It doesn't exist. I don't recommend checking against an RDP after a dive in any event. You plan your dive before you hit the water, or you be prepared and knowledgeable about a computer. You don't see the pilot checking his charts after he lands your plane, that was done well in advance.

Everyone on this board is so terrified of computer failure, but when we fly our hands are beholden to ILS systems and no one bats an eye. There are contingencies you need to learn. Dive with a buddy that also has their own computer, preferrably similar to your own. Stay close to them. If your computer takes a hit, you will be missing dives for the next few hours, but at least you have a reasonable sense you have not done anything stupid to your nitrogen uptake. If you are that terrified about a computer shutdown, you do what most guides do, find the simplest, least expensive computer, and dive with two of them, you have added your own redundant system. If this sounds extravagant, reach out and find someone's computer to borrow for your trip, so that you have a redundant system.

I am not saying you can't run a multi-level profile as safely, without loosing any time on the Wheel. But you have to make your choice UP-FRONT. RDP or Computer. There is no 'trust-me' or 'spot-check' diving allowed.

 

[FatCat]

Please explain how computers help you have longer dives. Also, I've heard that some dive charters insist on computers. I just returned from my first big dive trip to Cozumel and we all had high-end computers. The DMs gave us our minimum PSI and when we reached it we started heading toward our safety stops. Computers didn't have any impact on the length our 2-tank, am dives.
Rex

As others have said, computers extend your no-decompression limits by eliminating unnecessary or exaggerated rounding. Your instructor should have explained this to you in your basic course. You might want to revisit your manual.

Remember that even with tables, you run the risk of getting bent. Computers are far less pessimistic than tables (see above) so you have to be careful not to push the limits of what your computer will allow you by way of NDL.

Also, if you want to go into decompression diving, remember that most mainstream computers are not designed for deco-diving. Most will give you stop times and depths, but it is not their primary function.

Too many references have been made to nitrogen loading! A computer DOES NOT TRACK YOUR NITROGEN LOADING!

It only tracks theoretical nitrogen loading according to a mathematical model. This model has nothing whatsoever to do with your body. Or anyone else's body for that matter. Even if you set your computer to a more conservative setting, your computer does not know how well rested you are or how stressed or how hydrated or how hungover or... You get it, right?

 

[kevink]

Too many references have been made to nitrogen loading! A computer DOES NOT TRACK YOUR NITROGEN LOADING!

It only tracks theoretical nitrogen loading according to a mathematical model. This model has nothing whatsoever to do with your body. Or anyone else's body for that matter. Even if you set your computer to a more conservative setting, your computer does not know how well rested you are or how stressed or how hydrated or how hungover or... You get it, right?

Sorry for throwing around Nitrogen Loading. Tables won't track nitrogen loading either. A computer is making a theoretical model of your nitrogen uptake, the same can't be said for a table unless you run a religious square profile.

On the upside tables are also based upon mathematical models with many more actual dives to prove their statistics out. Computer models tend to be approximations of these tables. Either way, if you are not in decent physical shape (like the Navy Divers that proved out the first Navy tables) you should bias your own personal NDL accordingly.

Short of a post-mortem I can't think of anything that will show actual Nitrogen Loading. Hell even a laser doppler is only showing nitrogen that has come out of solution. In short you can never know YOUR own nitrogen loading, only the coroner will.

 

[Buoyant1]

I am not saying you can't run a multi-level profile as safely, without loosing any time on the Wheel. But you have to make your choice UP-FRONT. RDP or Computer. There is no 'trust-me' or 'spot-check' diving allowed.

I'm no where near a multi-level profile..my redundant system is my RDP and what info I get from my gauge and my old trusty Casio (good to 200 meters hahaha!) The fact that most of my dives have been within 25-35 feet makes 'multi level' easier to figure out (hmmm should I use 35 feet or 35 feet?)

Can't speak for the dude I dove with in July...I was still learning and he's the "pro". My guess is that he does so many shallow dives, that it's moot....but he wants to check his times. As I said, I can't speak....

 

[cmcarver]

On a single dive the computer doesn't extend my bottom time over the RDP. But where it helps is with the repetitive dives. I tend to have short SI at the local quarry and if I figure RNT on the RDP my second dive to 55' would be cut short by over 10 minutes. But since the path lines in the quarry are around 15'-25' I get credit for the swim time to and from the depth so I end up no where near the limits on the computer. It doesn't hurt to check the RDP before each dive for your square profile incase you have a computer problem you will at least have a fall back plan. I ran into that in December when my computer stopped working 1/2 way thru the dive.

 

[Buoyant1]

Amen to that! Beat's sitting out dive number two because of a little beeping hockey puck!

...snip... It doesn't hurt to check the RDP before each dive for your square profile incase you have a computer problem you will at least have a fall back plan. I ran into that in December when my computer stopped working 1/2 way thru the dive.