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    Re: When did "time sights" fade away?
    From: John Brown
    Date: 2011 Jul 13, 03:17 -0700

    Hello Frank

    I wrote:
    "Incidentally, our position lines were invariably obtained using 5-figure logs and the cosine/ haversine formula. For an acceptable, but lesser precision, some of us began to use Burton's 4-figure tables and the cosine/versine alternative, which, with experience and a good pro-forma, was quicker than many so-called short method tables, but obviously not as speedy and convenient as HO 249/AP3270. Azimuths were calculated using ABC tables."

    You wrote:
    "That's really interesting. Even as "New Navigation," these methods would surely have been counted as rather old-fashioned by 1961. Not that they wouldn't work, of course. And that seems to be a long-standing feature in the history of navigation. Methods don't get thrown out until the generation who first grew to love them finally stops teaching them."

    I suppose that the late fifties/early sixties were a time of transition from the Old to the New navigation, with elements of both in common use in British merchant shipping. Time sights for longitude had disappeared and the “non-specific” position line was the fundamental concept, except that the ritual of a noon observation for latitude persisted. The only direct position line plotting was done for star sights, all other transferred position lines were advanced or retarded by traverse table, or by slide rule using plain sailing formulae.
    Generally, British ship owners supplied the charts, sailing directions, chronometers and almanacs. All else was the personal property of the deck officers, who each owned a sextant and generally just one volume of nautical tables, either Norie’s or Burton’s.

    I have a copy of Myerscough and Hamilton’s Rapid Navigation Tables, published in 1939 and acquired for interest, long after I ceased sailing deep sea for a living. Like some other short method tables, the trig is based on Napier’s Rules, in this case with a perpendicular being dropped from the zenith to the hour circle of the celestial body. I get a slight headache looking at the rules in the Explanation to the Tables. Much easier to use the cosine, ha/versine formulae!

    A note in the Explanation has this to say:
    “It is common practice amongst marine navigators to obtain a longitude by observation when the sun is near the prime vertical and to “run up” this position to noon, when an observation of the sun for latitude may be obtained.”

    The 3rd Mate on my second ship bought a copy of HO249 when we called at San Francisco in 1963. This was a (late?) beginning of the end for the log tables!



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