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    Re: Interpolation to latitude
    From: Greg Rudzinski
    Date: 2009 Nov 15, 12:30 -0800

    For the US Merchant ships that I served on time changes were made when
    within 7.5� of the time zone meridian. On fast ships such as the older
    steam turbine Sealand SL-7 container ships (32 kts x 24 = 768 NM days
    run) time was sometimes advanced or retarded two hours in a day when
    two zones were crossed in a 24 hour period. Some modern ships have a
    clock system on the bridge that advances or retards every clock
    onboard. Time was advanced (traveling toward the rising sun) at 0001
    to 0101 (23 hr. day) or retarded (traveling away from the rising sun)
    at 0101 to 0001 (25 hr.day) LMT hours. Watch standers would stand an
    extra 20 minutes for 25 hour days and 20 minutes less for 23 hour days
    between 2000 - 2400, 0000 -0400, 0400 -0800 so that meal hours and day
    work would not be disrupted. The standby able seaman would call the
    oncoming watch at the appropriate time. Callout times were posted on
    the bridge chalk board. Upcoming time changes were posted on galley
    chalk boards. The engine room would be notified at the moment of a
    time change for a synchronized setting and log entry.
    On Nov 15, 1:05�am, "George Huxtable"  wrote:
    > 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
    > alive."
    > ===============
    > 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
    > me.
    > 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
    > watches.
    > 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.
    > George.
    > contact George Huxtable, at �geo...@hux.me.uk
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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