Reasons NOT to Use a Computer for a New Diver?

[Scott from LongIsland]

Recently a newly certified diver asked for some advice on the type of computer to buy. One person (a tech diver) says that nobody should ever use computers in either recreational or tech diving. I asked for rationale and was provided with none.

Can anyone offer solid reasons for a newly certified diver (recreational diving only) to not dive with a computer? Please no references to computers and tech diving. only recreational diving for this discussion.

 

[JamesK]

A lot of people feel that using a computer just teaches you to blindly follow your computer without knowing why it is doing what it is doing.


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[drrich2]

And using tables can lead dives to blindly follow tables, without a particularly good understanding of what they're doing or how, anymore than a computer.

Particularly since a computer can show progressive nitrogen loading, much as tables can.

Tables do offer the ability to plan a dive with nitrogen loading and NDL limits in mind; many people don't know how to do that with their computers. So, if you plan a dive to the Florida Keys, and figure on a 90 foot dive of the Spiegel Grove, tables will tell you at a glance how long you can stay down.

But a computer will give you credit for time spent at less than max. depth and let you stay down longer, if your gas holds out.

Some people believe that working with tables engrains a better grasp of nitrogen build-up as related to depth and time rather than using a computer from the get-go.

I'm a computer fan. You can still plan some dives with tables if you like, even if you use a computer from the start. Why deny yourself choice?

Richard.

 

[TMHeimer]

I can't think of a reason why a new diver shouldn't use one, provided he has been adequately trained. I would like to see instructors telling them that the (theoretical) bottom time limits a computer shows are "exactly" the bottom time remaining, as opposed to the little bit more conservative the tables are. Ei. if your max depth reads 80' on your analog gauge your average depth (even on a square profile) is really 77' unless your nose is in the sand. Logic says this COULD be the difference in DCS or not.

 

[MXGratefulDiver]

Recently a newly certified diver asked for some advice on the type of computer to buy. One person (a tech diver) says that nobody should ever use computers in either recreational or tech diving. I asked for rationale and was provided with none.

It's the internet ... people offer all kinds of advice, usually based on nothing more than their own personal preferences, or simply repeating something they were told and chose to believe.

If someone cannot articulate the "why" behind their advice, a good rule of thumb would be to consider that they don't really understand what they're talking about.

Can anyone offer solid reasons for a newly certified diver (recreational diving only) to not dive with a computer?

Solid reasons? No ...

Some people believe that using a dive computer leads to reliance on a device that you don't need to put any effort into understanding ... and that it's easy to misinterpret what the computer is telling you. There's a contingent of divers who believe that all you really need is a depth gauge and bottom timer, and some mental calculations for determining "minimum deco". While that works reasonably well at the recreational level, it's just one of several approaches that works reasonably well. Dive computers are relatively inexpensive and provide a handy way for the recreational diver to stay within no-decompression limits. As long as the diver makes an effort to understand how to interpret the data the computer is providing, there is no downside to using it.

... Bob (Grateful Diver)

 

[Phil_C]

To my mind the theory behind both is the same. The lessons - of a good class - should explain how the biology of nitrogen accumulation/diespersion works, and both methods of dive planning and monitoring, so the theory is there for the student, but after that I would always recommend a personal (as in not a borrowed for a single dive) dive computer.

My rationale would be that as long as it does not fail, the computer will keep an ACCURATE track of depth and time. Tables, unless you calculate multi level dives, will only ever give you a square profile and who do you know who tracks depths and times throughout a recreational dive so you can work out exact loadings afterwards. I don't know anyone who does.

If a dive computer fails then that really is no problem - just call the dive, give it a safe surface interval (24 hours if necessary) and start diving again. OK after a aggressive series of dives you may want to factor that in before diving again, but generally it shouldn't be a problem.

I can see absolutely no reason NOT to use a computer for every dive as soon as you can beg, borrow or steal one.

I only ever check tables to give me a heads up to total bottom times if I am planning dives, and more often than not I will use planning mode on the computer for that to take into account my recent dive profiles.

Phil

 

[boulderjohn]

There is a body of thought among some divers that computers are the spawn of Satan. I used to dive with such a group. I used to have an instructor who would not allow any use of computers on dives. That group still believes that. I am no longer part of that group.

One thing I heard frequently then is that you should not reply on a computer that may give you faulty data without you realizing it. You should instead rely upon "the computer between your ears," which will not make such errors.

One day two of my friends in that group got DCS. They did everything on the dive as they were taught. They had a computer in gauge mode so that it was essentially a bottom timer that provided nothing but depth, time, etc. They used a mathematical process to calculate their ascent profile, based upon their average maximum depth. They calculated their average maximum depth by checking their depths regularly and keeping a running average. They used their timers to plan their ascent to their first deep stop, and they did all their ascent stops according to their calculated plan. They did everything right according to their teaching theory, and they still got bent. Why?

Because they used a computer in gauge mode for depth and time, they were able to get a precise profile of the actual dive on their computer, and we all analyzed it. It turns out that their average maximum depth was about 8 feet deeper than they thought. It turns out that they took about 3 times as long as they thought they did getting to their first deep stop, which greatly added to their bottom times. It turns out they ended their decompression about 3 minutes early, although it is not clear whether they miscalculated the amount of decompression they would need or if they mistimed it.

The group is still committed to trusting the computer between the ears--after all, it is possible for a computer to make a mistake. The technical instructor to whom you spoke may be part of such a group.

 

[Steve_C]

i think that they should learn to use the computer from the start and by learn I mean show that they know how to computerize an ascent and also what to do if they run out of NDL. Not saying they should be told they can do deco but stuff happens.

In typical NC diving say on the Hyde which is often dove by fairly new divers it is 60 ft to the deck and supposedly 80 ft to the sand. They have no idea how long at what level. If they plan two 80 ft dives it is way too conservative.

There is always the chance of open water ascents. With a computer it is easy to maintain a safe ascent rate. Even when going up the anchor line the computer provides a reliable way to ascend. And it is usually much slower than the typical OW diver wants to go.

So they plan on 80ft because that is what the DM said during the briefing. They are cruising around the bottom of the boat and pass around the bow or stern. Unless they are watching their depth the whole time they will not realize that they were just at 87-89 where there is a wide depression. Even if they see that, oops they are deeper than planned what now?

Finally, suppose that they are diving on a lower viz day. They have not dove the ship a dozen times. They and their buddy have trouble finding the anchor line. They remember where it is. Choice is an open water ascent or to hit the anchor line with a little deco obligation. Computer gives them the option, given enough air, to go to the anchor line and assuming they can read their computer do the required extra stop and make a safe ascent.

Many NC divers dive HP 100s, some larger. Most of my dives are NDL limited and not air.

Finally often I instabuddy with fairly new and totally new divers. Sometimes the buddy they came with does not do dive 2 for some reason. Unless I am in the keys on 30 ft dives, I will not dive with somebody in NC who is just using tables on Rec dives. I would give up two much dive time after a 1.5-2.5 hour boat ride.

With the exception of some fossil hunting on a fossil ledge which is actually pretty flat, all dives are multi-level dives that easily range over 15-20 ft.

PS: I dive two computers

 

[KeithG]

The only possible advantage of tables only approach that I can think of is that table users are forced to figure out their NDL BEFORE their dive. So they have some awareness of time limits before they splash.

Computer users are not FORCED to do this. I very rarely see divers checking their computers before they jump in. The general behavior appears to be jump in the water, ride the computer. With very little forethought or pre-planning. They get surprised in the "middle" of their dive when the computer indicates they have zero NDL left at 80 feet.

 

[JamesK]

The only possible advantage of tables only approach that I can think of is that table users are forced to figure out their NDL BEFORE their dive. So they have some awareness of time limits before they splash.

Computer users are not FORCED to do this. I very rarely see divers checking their computers before they jump in. The general behavior appears to be jump in the water, ride the computer. With very little forethought or pre-planning. They get surprised in the "middle" of their dive when the computer indicates they have zero NDL left at 80 feet.

Exactly.


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