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    Logs vs Knotmeters
    From: Lu Abel
    Date: 2008 Mar 29, 17:56 -0700

    In another group I belong to, there's a discussion going on about the
    accuracy of speed measurements needed for Dead Reckoning (or Ded
    Reckoning for some purists).
    Dead Reckoning is really based on distance traveled.   So if I measure
    vessel speed, I have to go through a speed x time = distance calculation.
    A very long time ago, navigators measured vessel speed (eg, by counting
    knots pulled through one's fingers from a chip log, hence our term
    "knots") and then did a speed to time conversion.
    Somewhere along the line, patent logs (such as the Walker log) were
    invented and distance was measured directly by trailing the log's
    spinner.   When?
    And if anyone keeps DR plots any more, what technique is used today?
    Are electronic paddlewheel knotmeters considered sufficiently accurate
    to go back to calculating distance from speed?   (and at the same time
    I'll note that electronic knotmeters typically have a log function, so
    why bother with distance from speed and time calculations?).
    Lu Abel
    Navigation List archive: www.fer3.com/arc
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