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    Re: A navigation exercise
    From: Jeremy C
    Date: 2010 Apr 7, 10:43 EDT
    I neglected to note on my scrap paper the course and speed, but i went to the hourly logs and found the course to be 108 degrees True and speed 8.2 knots at the time of the lunar. 
    In a message dated 3/28/2010 2:57:28 P.M. Bangladesh Standard Time, antoine.m.couette@club-internet.fr writes:

    Hello Jeremy,

    Nice to read you again !

    Please find here after some results and the way I caculate them.

    Date 24 Mar 2010, deltaT = 66.8s


    Here I interpret your "un-named star" just as the very one closest from our Earth :-))

    No choice but assuming that it is a SUN apparent culmination exactly North of the Observer at UT=07h18m00s0

    Therefore, get the Sun Apparent coordinates for that moment :

    DEC = 01°24'4 and GHA = 287°54'6 (which stands on the Meridian of Longitude E 072°05'4) , and then

    assume that your position is E 072°05'4 and - from Sextant Altitude - also assume that your latitude is about 07°30' south of Laitude 01°24'4 North.

    Accordingly with the following estimated position S06°00'0 E072°05'4 , we compute a LOP with the Sun LL Height.

    Our LOP results are i = -55.6 NM(A) and (as expected) Z = 0.0°

    We can then guess our "Best Position Estimate" as follows :

    Time = 07h18m00s0 UT, S 06°55'6 E 072°05'4

    Certainly the Longitude is somewhat inaccurate, but the Laitude should be quite accpetable.

    And as a result ... both Peter and Kermit are also onboard your ship. Any booze ?


    I will do the computation with the following data and assumptions :

    - Observer's Position is close from the one computed hereabove, and

    - the Sun-Moon distance is 102°43'8 (corrected for sextant error)

    - the average heights are as follows : SUNN LL = 44°49'5 (cfse) and MOON UL = 23°57'85 (cfse), and

    - all observations are assumed to be performed at the very same time from a non-moving vessel. I think that, for lack of complementary information, I am using the published data to the best of the information they can give us.

    With the data and the assumptions detailed here-above, we get the following results :

    Time of Observation : 10h15m23.9s UT, and position at time of observation :

    S07°05'5 E072°06'0

    Had we had slightly different an observations order, i.e. after Sun-Moon Distance first Moon UL and then Sun LL - instead of actual Sun then Moon - we might have had possibly better results since the average Times values for both the Sun and the Moon Heights might have been closer from the time of observing their distance.

    Anyway, this Lunar derived position does not seem totall unrealistic when compared to the one obtained some 6 hours earlier for your Sun Noon height.

    If these results were of any reliability, we could even guess that you were slowly sailing towards the south at @ 1.5 KT. However I strongly doubt that you were just moving at such a slow speed on your big Merchant vessel !

    Best Regards

    Antoine M. "Kermit" Couëtte

    PS : Just expecting your published GPS derived results now ...
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