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    Re: DR plotting techniques
    From: Jim Thompson
    Date: 2003 Oct 18, 07:30 -0300

    That's why I like waypoints connected by route lines.  On a longer crossing,
    I watch the tide, wind, compass heading and GPS chartplotter route line.  I
    estimate the heading I need to steer to correct for leeway and current, then
    follow that for a while.  If the GPS trackline starts to fall off the route
    line, then I correct the heading appropriately.  This method allows me to
    stay fairly close to the route line, without having to make large
    corrections.  I end up following a course that approximates the route line
    fairly well.
    See this page for some screenshots of the process I follow, which I think is
    a fairly efficient compromise.  In fact I doubt that I could do better if I
    tried to do the formal DR process, including calculating leeway and current
    vectors to derive headings.
    Jim Thompson
    Outgoing mail scanned by Norton Antivirus
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of George Huxtable
    > If the vessel was following a ground-track using GPS, waypoints would be
    > set at A and B, and a straight-line ground track drawn between them. The
    > helmsman would be commanded to steer West of South during the
    > first 6 hours
    > to keep to that track and counteract the tide, and then, later, East of
    > South, to do the same. In the case of a slow vessel, and a hot tide, the
    > attempt to keep to the straight track may even become impossible. But in
    > any case, those Eastings and Westings are quite counterproductive,
    > cancelling each other out, and are made at the expense of the Southing,
    > which in this case is all that matters. Sceptics may find that a simple
    > vector diagram will convince them, but are welcome to argue back if it
    > doesn't.

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