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    Re: log lines
    From: Trevor Kenchington
    Date: 2003 Jun 10, 23:26 -0300

    Dan Hogan wrote:
     > Walker type logs were intended for ocean passages, not for coastal
     > a dependable reading the log should trail at least 50 feet. That's a
    lot of
     > territory around a marina. With practice you can learn to read your
    wake to
     > within 0.5 Knots of speed. Otherwise I would use a Knotmeter.
    Conning your way around a marina isn't coastal cruising and taffrail
    logs very much were/are intended for the latter, as well as for ocean
    Judging instantaneous speed is all very well (whether by visual
    observation, Doppler log or anything in between) but how does that help
    determine distance off from distance run? Look closely at the methods of
    pre-electronic chartwork, as presented in countless textbooks, and you
    will see (I do anyway) techniques built around an assumption that the
    navigator knows distances run, not speeds.
    Sure, given a speed log (who invented the neologism "knotmeter"
    anyway?), you can integrate over time to get distance run but if you
    don't have electronics to do the integration for you, you will have to
    work at it. Big ships from before 1860 tended to hold a steady speed
    through the inertia of hull mass and carried a sufficient crew to stream
    a chip log at frequent intervals, while the officers could concentrate
    on such navigational tasks as maintaining a reckoning. Most of us are in
    a quite different position today.
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                          Science Serving the Fisheries

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