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Wisdom of trusting one's dive computer?

Discussion in 'Basic Scuba Discussions' started by CaveSloth, Nov 12, 2019.

  1. Divectionist

    Divectionist Solo Diver

    # of Dives: I just don't log dives
    Location: Gold Coast, Australia
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    I should add that I think it is ridiculous to keep the comp in gauge mode for rec diving purposes when one can benefit from its full capabilities.

    Whether one relies solely on it is an entirely different decision.

    Any redundancy is good.
     
  2. wstorms

    wstorms Angel Fish

    # of Dives: 1,000 - 2,499
    Location: Netherlands
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    Both. Your computer is designed to bring you back to the surface safely (with a decent margin usually) so you can follow it back to the surface. You can trust the info on the computer for any recreational dive.

    However, you want to avoid being totally dependent on the computer. This is where the pre dive planning comes in. Even if a computer fails, you want to have some idea of what's going on. You can use the planning mode on your computer (or an app, or tables) to create a dive plan that gives you an idea of the dive.

    The more you move to tec diving, the more crucial this planning becomes. GUE starts early with this (as others already mentioned). The "just use a bottom timer" approach originates from the necessity to plan anyway, combined with the (back in the day) high failure rate of computers. Nowadays GUE states that a computer (not just any, there are some specific requirements) can be used, but should always be used as a tool to validate the pre-made plan. So plan the dive, dive the plan and use your computer to validate that plan.
     
    KWS likes this.
  3. M-Cameron

    M-Cameron Nassau Grouper

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    think of it this way.....if youre driving your car and your fuel needle is on E, but the distance computer tells you that you have 200 miles of range, are you going to pull over for gas or keep going?........i think most of us would pull over and assume something is wrong with the computer.

    buuuut if were on E and the computer says we have 10 miles, well probably assume we actually have 10 miles left of fuel.

    i take the same approach to diving....ill plan my dive and get a baseline number, and ill try to dive more or less my plan and ill expect my dive computer to be more or less in the ballpark.

    but if im at 100' and my computer is telling me i have 60 min NDL......im going to assume its faulty and stick to my planned dive time.

    i feel computers are a safe and reliable method for timing recreational diving......but you are also responsible for your own safety, and responsible for knowing what you are doing.

    just the same way as if someone drove into a lake because "their GPS said to" is not an excuse.......blowing a deco limit because your computer "said to" isnt an excuse.
     
    Nirvana, KWS, PfcAJ and 4 others like this.
  4. johndiver999

    johndiver999 Manta Ray

    # of Dives: 500 - 999
    Location: Gainesville FL
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    Once my computer gives me "bad" information, I would probably end the dive (not continue the planned dive) unless it was super shallow or had redundant information that I trusted.
     
    KWS likes this.
  5. CAPTAIN SINBAD

    CAPTAIN SINBAD Divemaster Candidate

    # of Dives: 200 - 499
    Location: Woodbridge VA
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    I have another concern with these computer chasers. Decompression is not an exact science and my own observation tells me that there are significant number of divers out there who experience mild decompression symptoms while staying within the NDL limits projected by their computers. Traditionally, tables would assume a square profile and therefore had a safety cushion built into them but computers were developed so that you may chase the NDL right to its very end. Now those NDL limits are not as precise as they appear. In reality, if you are feeling cold then your computer should show a different NDL and if you are dehydrated then your computer should show a different NDL. Computer has no way of knowing if you are dehydrated, obese, cold so obviously, when a hard limit is projected to a wide population, some people will be bent.

    Technical divers deal with this dilemma by using gradient factors but recreational divers do not know enough to apply them. They are at the mercy of whatever limits the manufacturer has chosen to project at them. This is why if you were on a dive boat in North Carolina, a big percentage of people just fall into deep sleep on their way back from the dives. It should make people stop and think how could such a significant number of people on the same boat immediately have a "nap attack" in the middle of the day? Are they always this nappy at 2:00 pm when they are sitting at work? Then you look at a fishing boat where people have been out in the sea for the same time and no one is napping. Yet none of the sleepers on the dive boat will ever think that they are bent because their computers are telling them that they are safe. I have personally struggled to wake people up when the trip was over and they are all walking funny and complaining of headaches but it never occurs to them that this is what a mild decompression hit feels like because they trust their computers more than their own symptoms.

    Furthermore, there is a significant percentage that thinks that breathing nitrox makes them feel so much more energetic after the dive. Now there is no scientific reason that an unbent individual will feel better when they breath a higher percentage of O2 so these are obviously the people who were getting mild decompression symptoms like fatigue and lethargy after the dive. Being on nitrox prevents them from getting bent so the comparative lack of fatigue that they experience is what they regard as higher energy levels associated to richer O2 mix.

    My take is that while computers are very, very useful they are a supplement to your understanding of decompression. It is important to have a rough idea of how much time you have at a specific depth prior to jumping in Instead of jumping in and finding out. It is also important to realize that those limits on any given day may not apply to you and when you should not obey the computer and add your own layer of conservatism to the dive.
     
  6. M-Cameron

    M-Cameron Nassau Grouper

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    yeah i like to have redundant depth/ time gauges..and use my computer for convenience.....so it would make no sense to call off a dive because i can still safely dive my plan.

    if my computer was my only method to measure time and depth, then yeah ide just surface and end the dive.
     
  7. scrane

    scrane Manta Ray

    # of Dives: 500 - 999
    Location: Boise, ID.
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    Yes. Within the realm of situational awareness.
     
    undrwater likes this.
  8. broncobowsher

    broncobowsher Solo Diver

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    Unless the computer is a real POS, leave it in computer mode.

    Plan your dive, the computer should match your planning if you did it right. The Teric is a real computer, it will do everything you will ever need it to do and more. No reason to make it a gauge and bottom timer. Yes, you should be able to plan a dive on a cut set of tables with a timer and depth gauge, but there is no reason that you should do it every time.

    I only know of a few people who actually cut tables and use a bottom timer. They don't have computers capable of multiple gasses during a dive. Everyone else (who runs a Shearwater) just runs the computer. Often 2 computers so there is a backup.
     
  9. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
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    Good post overall, but recreational divers do have conservatism options on most modern computers, which is a simplified way of doing what gradient factors do.
     
  10. runsongas

    runsongas Great White

    # of Dives: 500 - 999
    Location: California - Bay Area
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    Buhlmann with GF: Google Maps

    pseudo RBGM and other proprietary algorithms: Apple Maps

    Multi Deco Cut Tables: Handwritten Route Directions

    Tables + Bottom Timer: Rand McNally Paper Map + Compass

    Ratio Deco: Driving around while refusing to ask for directions because you totes know how to get there brah
     

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