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    Re: GPS jamming concerns
    From: Mark Coady
    Date: 2016 Aug 10, 10:15 -0700

    Indeed, like my love of the very reliable sun and stars, my thoughts are that GPS is one of the greatest tools in the navigator’s arsenal. It enables me to dive on wrecks with unimaginable accuracy. It is just that any input to our position and planned safe path has a probability of error related to either the accuracy of the data itself, our interpretation of it.  GPS is more statistically likely to be a human error hazard, as we get so pampered by its amazing properties we may get complacent with our interpretive skills, or we fail to confirm that the charts and data in it are properly updated.  

     I laughingly used to joke about right here in little Noank......West Cove has a quite substantial breakwall in it...... it was placed in 1986 after hurricane Gloria to reduce future hurricane damage.  It was enlarged several times, and was a huge save in Sandy.  Due to the permit completion filing it actually did not appear on the official NOAA charts until 2011.  A rock wall 1/4 mile long and 6-8 feet out of the water is a tad bit of a concern for a small vessel.....  It is still not on one of my two GPS's, because it has an older chart in it.  Much of our area has not been resurveyed in over 50 years.  There are some changes  here wrought by storms and currents and man that are a potential risk...and they are not on anything but the locals brain cells.

    I love my paper, but it too has similar limitations. Paper plotting is most certainly vulnerable to error. We make math errors; we get tired, read or transcribe a number wrong.  Some of our charts here are out of date or simply wrong in spots. (It is of course safer to keep to the deeper main routes in shallow doubtful areas).

    It is the sum of all my tools and their crosschecks, and confidence in the probable accuracy of any specific one at any time that is (hopefully) the key. I may weight one tool more than another on a certain day, based on my confidence in it. Radar, sounders, gathering local knowledge, paper charts, GPS, reading water surface patterns and wave action, tide tables, water colors and shading, etc. (did I say I really miss Loran C?)... 

    In essence, my decisions regarding course  are based on my assessment of the safety of the inputs.  I may choose longer & deeper routes if I doubt my data, when running between places, and other times in a flat calm I may nervously hunt for a wreck in shallow unfamiliar waters, borderline paranoid and using every tool I have to avoid bumping into solid things.  

     The big problem I find in some parts of the world is the data is more sparse, at times just plain wrong, or the confidence is low.... making the navigators job particularly challenging  and frankly.... risky.

    Honestly I have tried to minimize risk as I have gotten older. There are places you just don't have enough accurate info to be safe. In my younger days, I made some overconfident mistakes singlehanding in bad weather that could have turned out very badly.  Fortunately my stupidity is offset somewhat by resourcefulness and determination....and they turned out ok....but I was humbled and learned to use more caution....

    I in fact I love my GPS, as my "crewmember" I would consider it far more reliable and accurate  at its job  than I. Used with measured care, it makes me fantastically safer...but the old acronym GIGO always holds true in navigation....   Garbage In, Garbage Out ....

    and of course......

    It is impossible to make something foolproof, as fools are so ingenious....


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