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    Re: Time Sight usage
    From: Antoine Couëtte
    Date: 2013 Jan 13, 22:21 -0800


    Thanks for your kind comments.

    We can conclude from previous results that the N05d05'8 W001d13'9 Position observed by the Navigator through 5 SUN Latitude Observations [all SUN Azimuths close to 180d] and 2 STARS Longitude Observations [SIRIUS (Z=123.4d) and PROCYON (Z=087.6d)] is confirmed by to-day LOP's since I found the Navigator position to be at N05d05'802 W001d13'853, i.e. not even 300ft from his own results.

    Accordingly the Navigator's determination of Cape Coast Castle Lighthouse position remains unchanged at N05d06'5 W001d14'6 .

    However :

    From Google Earth, a better determination of this Lightouse position (not clearly visible itself but with Cape Coast castle clearly visible) is rather :
    N05d06'2 W001d14'4
    The Lighthouse position determined by the Navigator is a little better (0.4 NM error) than the previous Bowditch (1938) position at N05d06' W001d14'(0.8 NM error).

    Hence my questions :

    1 - Strange way to attempt refining a Lighthouse position from a somewhat uncertain Offset anchored position at sea, no ? Theodolite observations from the Castle itself would have yielded a much better Position fix, but maybe were not possible then ...

    2 - Strange Azimuth computation error from the Navigator for SIRIUS, one of the only 2 bodies used for Longitude determination. Current determination is 123d4 while the Navigator computed 106d38'7, and in spite of a 17 degree error on the computed Azimuth, the Navigator derived Longitude is exactly the same as the one determined from PROCYON, a body almost due East for which there is no
    computed Azimuth error ...

    Any cues here from anybody ? First of all, it might be useful to perform these same computations through different Software (Andres, Peter, Paul, or Other ?), just to independently crosscheck that I have not made any error.


    [NavList] Re: [NavList 21924] Re: Time Sight usage
    From: Henry Halboth
    Date: 13 Jan 2013 21:15

    Your assumptions with respect to time and altitude corrections are entirely correct.

    Thank you so very much for your interest.



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