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    Re: Leg 83
    From: Arthur Pearson
    Date: 2002 Sep 24, 15:30 -0400

    My math was right with the old tables, I just was using the wrong
    destination because I did not read the problem carefully. When I worked the
    numbers using the correct destination point, I got the same result as you by
    all methods. I agree that the old tables are tricky to use, but it does make
    you think hard about exactly how you are solving the triangle (what parts do
    I know, which do I solve for in what order) and what units you are using
    (change in lat and departure, or change in long and meridonal parts).  Good
    mental exercise and good practice for the day you drop the calculator in the
    I did use a vector diagram to figure the adjustment for current which was a
    good dust off of something I haven't done in while.  I am curious if there
    are formulas that could be programmed that would take as inputs the plotted
    (or calculated) course, the speed through the water and the set and drift of
    the current and which would then ouput the adjustment needed (or course to
    steer) to compensate for the current and make good the plotted course.
    Great fun these problems, with all sorts of interesting tangents, thanks for
    putting them together.
    ----Original Message Follows----
    From: Dan Hogan 
    Reply-To: dhhogan1@EARTHLINK.NET
    Subject: Re: Leg 83
    Date: Tue, 24 Sep 2002 06:50:51 -0700
    Using the "really old way of navigation" is prone to errors. If the
    arithmetic is OK then Q2 TC should come out close to 285d. After that the
    most accurate way to manually calculate CC is using a vector plot.
    P.S. On a previous post to you I noted that there ia a possible error in my
    CelestNav v. 2.3.2 Mercator calculations.
    The DR problems for Silicon Sea are calculated with Navpo93 from NAVIG which
    are Rhumb Line. I double check them with an HP 32SII Mercator program from
    "The Calculator Afloat" by Shufeldt & Newcomer.
    On 22 Sep 2002, at 22:33, Arthur Pearson wrote:
     > Peter et. al.
     > Many thanks for these exercises, they are a great project now that the
     > boat is put away for the winter and we have to find another way to keep
     > the skills fresh.
     > I am consistently getting 290d True for Q2 below. I am using 1958
     > Bowditch Traverse tables and I have worked the problem as a Mercator
     > Sailing (looking up the MP's of the two latitudes to get m, dividing
     > that into DLo, using that ratio to get a NW bearing) and as a Mid
     > Latitude Sailing (using DLo at 19d and 20d to interpolate for departure
     > (p) and dividing by change in latitude (l) and using that ratio to get a
     > NW bearing. Both methods bring me to 290d as does my PalmPilot running
     > CelestNav for a Mercator Sailing. In no case can I find my way to 285d.
     > I concur that the adjustment for current is about -1d and the combined
     > variation and deviation is -11d, bringing me to a course to steer of
     > 278d.
     > Where have I strayed?
     > Arthur
    Arthur Pearson
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