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    Changing Zone Descriptions at Sea
    From: Jeremy C
    Date: 2009 Nov 15, 15:12 EST
    I will add to Henry's description of how time is changed at sea.  He is correct, the MOST ships still maintain the three 20-minute changes during the evening watches.  I do have one captain who defies tradition, as is his derogative, and changed it one hour at a time.  The trick was that he would switch watches that this was done on as we entered each new time zone.  For example, for the first change the 8x12 would do it at 2200 hours.  For the next zone the 12x4 would do it at 0200, and finally the 4x8 would do the third change at 0500.  This makes all time changes outside of the work hours of all but the two people on the bridge and would not cause major confusion (usually).
    The reason for the 20 minute changes is indeed to spread the pain or sleep bonus among the three watches.  The normal times are 2200, 0200, and 0600 so as not to interfere with people's work schedule.  To be frank, typically the watch officer hits the "advance" or "retard" button on the master clock when he wants to.  For example, when I do it on the 4x8 watch, i do it soon after I arrive, so between 0400 and 0430.  It doesn't really matter at that point.
    The navigational time it is COMPLETELY different.  The DR's, fixes, all of that, are retarded the WHOLE hour at 0200 on the 2nd Mate's watch (he's the navigator.).  He usually also does the bridge clocks (not hooked up to the ship's master clock) at this time as well.  So you will see either no 0200 fix, or two 0200 fixes depending on what direction we are traveling, as well as a note in the deck log book about advancing or retarding the clock 1 hour to conform to a particular time zone.
    I suspect that this may have been done on the 4x8 watches in times past due to the fact that the 4x8 were traditionally the 2nd mate watches.  Perhaps Henry can weigh in on that point.
    For some very fast ships, I have also heard of 2 hour changes in a night.  I have no personal knowledge on how that is done.  I suspect 40 minutes per watch.

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