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    Re: Role of CN at sea, was Re: Averaging sights ...
    From: Bill B
    Date: 2004 Oct 12, 19:15 -0500

    > Has anyone ever heard of a vessel loosing all of its GPSs while at
    > sea?  If it hasn't happened yet, I suspect it will.
    In approx.. 700 hours of land and water operation over the past 3 years, I
    have experienced five loss-of-satellites-signal situations, usually lasting
    from 5-15 minutes.  Three were on land, one due to a detour through the
    mountains in Pennsylvania after a 50 car/truck pile up in front of me.  With
    mountains on all horizons and a blinding snowstorm overhead, would hardly
    blame that on the system or unit.
    The other two land situations I have no explanation for.  Great weather,
    flatlands, no military bases nearby.
    Of the two on water (Lake Michigan) all units (my Garmin 76, an older
    Magellan, and the owners chartplotter) all failed to get adequate signals
    for 10 minutes or so. Partly cloudy sky.  In one case an older Garmin showed
    our speed-over-ground on a broad reach in a 34' Catalina as 33.8 kn.  Not
    too shabby--lucky the rudder stayed attached ;-)
    I have seen people sit on their unit left on the cockpit cushion and it lost
    all of its waypoints.  A friend's older Magellan unit failed to find
    satellites after 3 hours.  It is been replaced by a new unit.  Have also
    seen two different Loran C units go haywire, with errors of more than 5' lat
    and lon.
    In talking with about a dozen sailors on the 600 dock at Michigan City, each
    and every one of them has experienced unexplainable signal loss of 5-15
    minutes while on the water.
    Perhaps the Great Lakes don't meet the definition of "at sea," and is mostly
    coastal piloting, but there is ample evidence a single unit can malfunction,
    and even with multiple units, there are periods where signals cannot be
    Not a big deal on the southern half of Lake Michigan where it is pretty much
    point-and-shoot, but uncomfortable in the area where Michigan, Huron, and
    Superior merge.

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