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    Re: DR vs EP vs MPP vs Fix vs Running fix
    From: Chuck Griffiths
    Date: 2002 Feb 8, 10:42 -0500

    In answer to the poll, I've checked with my sailing friends and  after rereading
    a couple reference texts in addition to Bowditch we've all come to the following
    conclusion - we badly misuse the term DR position. Yes, I've always taken leeway
    and estimated set and drift into account and called that my DR. I can't however
    find a reference that suggests that one should call such a position anything
    other than EP. My 1975 Bowditch does concedes that in the "time of sailing
    ships" leeway was included by some in the DR, but it is quite clear that the DR
    needs to be corrected for estimated set and drift to arrive at EP. The resulting
    line from departure to such EP is labeled with "course made good". After a fix
    (a true fix not DR or running fix) the line drawn from departure to the fix is
    labeled "course over ground" actual set and drift can now be calculated.
    
    In lieu of "course made good" Richard Hobbs'"Marine Navigation" (Which is a text
    book used at Annapolis.) says the DR line is labeled with course(C) and
    speed(S). The line from departure to EP, after correcting for estimated set and
    drift, is labeled as "track"(TR) and "speed of advance"(SOA) and the line from
    departure to a fix is labeled with "course over ground"(COG) and "speed over
    ground"(SOG). I wish I plotted half that precisely.
    
    Chuck
    
    ____________________Reply Separator____________________
    Subject:    Re: DR vs EP vs MPP vs Fix vs Running fix
    Author: Jared Sherman 
    Date:       2/7/02 6:36 PM
    
    Chuck - and all-
     <"The DR position is only an approximate position because it does not allow
    for the effect of leeway, current, >
     Is there anyone here who would "reckon" their position without attemping to
    factor in ALL known effects? If one is plotting a DR position while crossing the
    Gulf Stream, even without knowing the current, is there anyone who would not
    indicate *some* offset as a best guess of the current, since they approximate
    current direction and speed are almost certain to exist to some extent?
    
    I ask this as a poll, not as an arguement. My understanding of DR, the good Mr.
    Bowditch aside, was that a navigator placed EVERYTHING he could into the DR
    position and that it was supposed to include all "guestimates" of where you
    actually were, not just ignoring the ones you couldn't specify to five decimal
    places.
    
    
    
    
    
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