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    Re: Interpolation to latitude
    From: George Huxtable
    Date: 2009 Nov 15, 09:05 -0000

    I had asked-
    "I've noticed that Jeremy's interesting postings contain many references to
    Zone Time, so it would be interesting to discover what US merchant vessel
    practice is, and exactly what happens when they shift into a different time
    zone. I can't say what the practice is in British merchant vessels; does
    anyone know? My guess would be that two chartroom clocks are kept running,
    one at GMT, one at Zone Time."
    To which Henry Halboth replied, in [10615]-
    "Did you really have to ask this one, or perhaps I have just misunderstood
    your intent?? Regardless, I will answer - if just to show that I am still
    Well, it was worthwhile asking that question, if only to discover that Henry
    was still going, and still sharp! Perhaps from one approaching fossildom
    himself, he won't mind being described as our oldest living fossil, having
    been at sea since 1936!
    I had thought I knew how timing was done at sea, but Jeremy's frequent
    references to Zone Time, which he has since explained, had rather surprised
    In another way, too, I'm glad I asked the question, because Henry's answer
    contained something that was quite new to me, and it's always good to learn.
    Henry wrote-
     "The ship's daily activities and all clocks associated therewith were
    regulated to Zone Time, generally advanced or retarded 20-minutes per night
    watch when passing from one zone to another, so as to maintain some
    semblance of normalcy in daily living and to be in coincidence with the time
    being kept at the port of intended destination on arrival there."
    That 20-minute business was quite new to me. Presumably, the aim was to
    spread the benefit (or pain) of a Zone change equally between all three
    Particularly in view of those 20-minute shifts, I wonder how bridge staff
    would be aware what  the adopted offset was, between GMT and ship time, at
    any moment. Was it somehow posted up in the bridge (and in the radio room
    also, when a ship had one, being the other place it needed to be known)? Or,
    did it have to be deduced from the difference between a GMT clock and a
    ship-time clock? Was there yet another clock, indicating zone time, where
    that differed from ship time? Whose responsiblity was it to make the
    necessary step-changes? Questions, questions...
    Henry added-
    "I did sail on one Panamanian Bark in the 1940s, from Panama City to Durban,
    aboard which LMT was kept and all daily activity clocks were reset at LAN,
    necessitating resetting to Zone Time on arrival at the port of destination.
    GMT was, however, kept by Chronometer when it was running. This was an
    unusual circumstance for the time."
    I hadn't realised that he had actually made ocean passages under sail, if
    that's what the reference to a "Panamanian Bark" implied. Indeed, that
    practice, of resetting ship's time to local time each noon was a hangover
    from the sailing ship era.
    I wish we could persuade Henry to tell us some tales from those days, that
    are still stowed away in his memory-locker.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    NavList message boards: www.fer3.com/arc
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