reason for two computers??

[jstuart1]

that when many of you got your computer you removed your depth gauge from your gear? Why? I am just a newby and am curious. My console has my compass, depth and SPG. I wanted to keep it that way for redundancy so I got a writst computer. One day I will probably go AI but will still keep my console the same for redundancy.

OK so I am a gauge nut but I like self sufficiency and redundancy. Occupational hazzard I guess since I handle the shutdown systems at the plant I work at. :11: 2oo3 voting on all critical systems.

 

[The Chairman]

I moved to the Sunnto Cobra, which is an air integrated Computer and replaced my entire console. I have never looked back. As I said before, seeing the data from it has changed my dive habits signifigantly. Slower ascents, more and longer stops being the most obvious.

 

[DareDevil]

...
But in reality computers are not necessary at all. A simple bottom timer and depth gauge suffice when used by someone with a rudimentary understanding of decompression theory and the self-discipline to take control of their dive.

You are totally right, a computer is not necessary, but it can be extremely useful. With a computer you can:

1) Have a longer dive: the computer will keep track of the saturation/de-saturation process in your body as you change your depth. With the equipment you described, you can't: all you can do is get the max depth, look at the watch and cross-check the table

2) Monitor the air flow: of course you can do that by looking at your pressure gauge from time to time, but the computer will do that more often. Besides, I am sure you agree there may be situations in which you are distressed or else and then you start to breath inconsciously, and perhaps in those situations you aren't exactly thinking "now should I monitor the air flow". The computer can do that for you ringing an alarm if you are using too much air: that will give you something to think about.

3) During night dives, pitch dark it is easy to drift up/down without even knowing it. You need a fixed point in space to be able to estimate your position... You may slowly change your depth without even knowing it, and a depth gauge usually it is a resolution of 1 meter (if you live in Europe). Now if you miss the fact you are drifting, you may change your depth and then your ascent rate may increase drastically. A computer can monitor the depth with a much better resolution (0.1 meter) and can ring an alarm if your ascent speed is too high. Again, if "everything is going well" you are already doing it with the other equipment you described, but things are not always going well.

4) The computer can monitor the air you are breathing and use that factor to evaluate your saturation. This can lead to a better "deco/no-deco" evaluation, increasing the safety factor. That you *can't* do with the equipment you described

I agree with you that it is redundant, but I think it can provide help and be really useful in certain situations. Just like a second 1st/2nd staget set, a backup torch, an emergency beacon or a zillion of other things.

I always dive with a computer, but also with an analog watch, a depth meter, a pressure meter and tables, two regulators. If the computer fails I abort the dive, just like if one of the regulators fails.

Cheers,

DareDevil

 

[hex92]

I bought a second computer for my girlfriend to use when we went on vacation. I have been using it when I dive without her as a backup. Why?

First of all I have done almost 120 dives on my computer and haven't changed the battery yet, so it will die soon. So I am covered with 2 computers in case one fails.

When it came time to decide on what computer to buy I thought about buying a Dive Rite and a couple of others but in the end I bought another Aeris2. The reason is obvious. Download cables are expensive and already had one for the Aeris. That saved me at least $75....and it was on sale.

 

[ianr33]

4) The computer can monitor the air you are breathing and use that factor to evaluate your saturation. This can lead to a better "deco/no-deco" evaluation, increasing the safety factor. That you *can't* do with the equipment you described

DareDevil

Huh ??!!

 

[RonFrank]

Computers are great, but IMO one should have at LEAST the NDL bottom time for the max depth in one's head before any dive in case the marvelous electronic device does quit during a dive. The other option is to terminate the dive immediately upon a computer failure.

It also depends upon how you are setup in the way of other gauges.

I have a wrist aeris II, but I also have a 3 gauge console. I use my watch which while not a high end model, does have a rotating bezel, stopwatch, and is water resistant to 200 atmospheres.... as advertised . I do have the watch pressure tested when I get the battery replaced.

So there is my backup stuff, wheel, watch, analog console.

My diving instructor carries two computers. His backup is just an older model that he stuffs in his BCD just in case. They are NOT the same model or even brand, but both do Nitrox which is what he dives with.

IMO a backup computer becomes more necessay the more you set yourself up to be dependent upon it.

Ron

Is there a good reason to have two dive computers? Should they bought be of the same brand? The one I dive with now has acted like. It didn’t want to work just one time. Its about three years old and I had just replaced the batteries. Except for that no problem.

 

[DareDevil]

Huh ??!!

An air-integrated computer may monitor the air flow and therefore take in account that a diver is for example breathing too much on the bottom because he/she is afraid, tired or whatever.

The increased breathing rate leads to absorb more Nitrogen than expected. As consequence, the computer may update the deco profile asking the diver to perform additional and/or longer "deco stops" to take in account the increased tissues saturation.

You can't do that with the tables, because the tables are based on a pre-defined saturation rate, which does not take in account what the diver is actually doing.

DareDevil

 

[DareDevil]

that when many of you got your computer you removed your depth gauge from your gear? Why? I am just a newby and am curious. My console has my compass, depth and SPG. I wanted to keep it that way for redundancy so I got a writst computer. One day I will probably go AI but will still keep my console the same for redundancy.

OK so I am a gauge nut but I like self sufficiency and redundancy. Occupational hazzard I guess since I handle the shutdown systems at the plant I work at. :11: 2oo3 voting on all critical systems.

I have a computer but since it is man made, it may fails. So I always dive with a air-integrated computer AND a watch, depth gauge, pressure gauge and tables.

Cheers,

DareDevil

 

[Mike Veitch]

Real world example for why you need two computers. Liveaboard diving somewhere out in the Pacific doing 4 or 5 dives per day.
On day three your computer fails: if you have a backup on your wrist or console or whatever, you can keep diving because it has been tracking your nitrogen.
No backup? Well, the boat can give you another computer to use but it has no idea about your nitrogen because it has been sitting in a cupboard. Guess you are out of the water for 12-24 hours...thats tough luck when you just spent $5000 to get where you always dreamed of diving.

And for those of you who don't use computers...you will find that on most liveaboards (at least those in the Pacific with set dive times, sheer walls, and strong currents) computers are required. No computer? Well you can try to dive tables, not much good for 5 dives/day with depths up to 100+ feet. Especially when (depending on incoming currents) the 4th dive of the day includes a drift dive to 90 feet at the mouth of a pass, drifting into the pass at 60 feet which is the shallowest depth. Air computer? 30 mins Diving Nitrox? probably get 45 mins. Tables? Sorry, you never even got in the water...
For $100 for the week i think even renting the computer is the smart way to go.

 

[rcohn]

Oh my yes... if you need one computer then you probably need two! I remember in one of my threads on mutilevel diving without a computer or tables one fellow was adamant that you should have two computers.... in fact I think he might have been in favor of three and polling them to see which one was to be believed.

But in reality computers are not necessary at all. A simple bottom timer and depth gauge suffice when used by someone with a rudimentary understanding of decompression theory and the self-discipline to take control of their dive.

I'm guessing you're refering to your "wonderful" profiling thread http://www.scubaboard.com/showthread.php?t=7840&page=1&pp=10&highlight=redundancy Where in post #30 (http://www.scubaboard.com/showpost.php?p=81609&postcount=30) in reply to your question

If you rely upon a computer then perhaps I agree that you should use multiple computers... if one is good, two is better, four is exponentially better, what is best?

I replied

High-reliability computer systems typically use three to four computers in a voting scheme. For example I'm told the bow plane control in a nuclear submarine use a four computer system. Aircraft flight controls are using similar systems.
1. Operating normally all four computers will match, the fourth computer provides redundancy.
2. When/if one computer deviates from the other three it is in error and removed from the system. Full capability still exists, you can detect and isolate malfunctions using three computers.
3. Now when/if another computer deviates from the other two, it is in error and removed from the system. Now you have reduced capability, you can still detect but you can no longer isolate malfunctions.
4. A deviation between the two remaining computers signals a problem exists but I don't know what steps are typically used to isolate the problem and remove the malfunctioning computer.

Of course, the nuclear submarines have 2.5 month deployments so the system need to work much longer than dive computer. And planes crash when the flight controls fail, remember you may be relying on a redundant computer system on you next trip.

For a diver, using dual computers allows problems to be detected. You always have the option of following the more conservative of the two computer readings to safely end the dive. With a buddy providing one or two additional computers you can identify which computer is malfunctioning and follow the working computer. If someone wants to use three computers that certainly won't cause any harm, but it's not required to detect a malfunction and safely conclude the dive.

I know I haven't been around for awhile but let's try to keep the record straight.

Ralph