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    Re: Bowditch (2002) Table 17
    From: Stan K
    Date: 2012 May 1, 03:26 -0400
    Well, just call me lazy.  There are so many errors on that page that I just assumed the lack of a dip correction might be just another error, without giving it any real thought.

    Thanks, Gary.

    Stan


    -----Original Message-----
    From: Gary LaPook <garylapook---.net>
    To: NavList <NavList@fer3.com>
    Sent: Tue, May 1, 2012 2:07 am
    Subject: [NavList] Re: Bowditch (2002) Table 17

    Obviously the enter the table with  "the height of eye of the observer in nautical miles;" is a typo. The reason you do not need to correct for dip in table 17 is that you are not measuring the height of an object using the visible horizon as the reference point as you would when measuring the altitude of a star. The height of eye is needed to determine the distance to the visible horizon so the angle below the horizon to the waterline of the object can be converted to the distance closer than the horizon can be determined and then tabulated as the distance from the observer. This is an interesting new table and was not in earlier editions of Bowditch.

    The purpose of the dip short of the horizon table always eluded me since you need to know accurately the distance from you to the intervening shoreline which means that you had to know where you were and if you knew that then why are you taking celestial observations in the first place. But it does make sense for ships in convoy since  a ship may be between you and the horizon on the azimuth of the star you are shooting and you can know the distance to the other ship accurately and measure the star from that ship's waterline even though you don't your location on the face of the globe.
    gl


    gl

    --- On Mon, 4/30/12, slk1000---.com <slk1000---.com> wrote:

    From: slk1000---.com <slk1000---.com>
    Subject: [NavList] Bowditch (2002) Table 17
    To: navlist@fer3.com
    Cc: slk1000---.com
    Date: Monday, April 30, 2012, 7:03 PM

    The more I look at page 560 of Bowditch 2002, the more I think this is another error, like the formula for Table 15 not having enough terms in the radicand.

    It says "The table is entered with the corrected vertical angle and the height of eye of the observer in nautical miles; the distance in yards is taken directly from the table."  The italics are original, but the table is entered with the height of eye in feet.

    In the description of  the formulas, it says "h is the height of eye of the observer in feet".  At this point it seems like the height of eye should be converted to nautical miles.  Then it says "ds is the distance to the waterline of the object in nautical miles."  This may be correct, just not converted to yards, but I'm too tired to think about it.

    Stan
       
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