Time-Keeping at Sea [from Mark Brader]

Paul Eggert eggert at twinsun.com
Sun May 15 07:10:24 UTC 2005

[Forwarded from Mark Brader.  Please note that he is not on the
mailing list; replies should be directed accordingly.]

From: msb at vex.net (Mark Brader)
Subject: Time-Keeping at Sea
To: eggert at twinsun.com
Date: Sun, 15 May 2005 00:52:33 -0400 (EDT)

Please forward this to the tz mailing list.  I am not on the list;
people should direct replies accordingly.

Your "australasia" file has this from Gwillim Law (2000-01-03):
# An Anglo-French Conference on Time-Keeping at Sea (June, 1917) agreed that
# legal time on the high seas would be zone time ...

A while back I emailed Gwillim to ask about his source for this
statement.  At the time he didn't remeber, but later he wrote back
and told me that it was Howse's "Greenwich Time and the Longitude".

Gwillim kindly transcribed the passage from Howse, saving me from
finding where my copy is:

| In June 1917, therefore, an Anglo-French Conference on Timekeeping at Sea
| assembled in London. This recommended that the zone-time system should be
| used at sea, clock changes required by changes of longitude being made
| preferably in one-hour steps. This recommendation was immediately adopted by
| British and French ships, both naval and mercantile. Ships of most other
| nations soon followed suit so that, by a few years after the war, zone time
| was kept at sea, certainly by almost all naval ships and by many non-naval
| ships as well. Nevertheless, up to the Second World War, the old practice of
| changing ship's time at midday prevailed in many independent merchant
| ships.

So if this is correct, the conference said nothing at all about *legal*
time; they only recommended a practice.  It also isn't clear from this
passage whether the recommendation was for the change to happen when
the specific meridian was actually crossed, or whether it was okay to
do it at a convenient time so long as you did it in one-hour steps.
(On the cruise ships I've been on, time zone changes were always done

It would be interesting to find the conference proceedings and see
how the conclusion was actually expressed, and to know whether there
actually is such a thing as legal time for some or all ships in
international waters.
Mark Brader   |  "Debugging had to be discovered.  I can remember
Toronto       |   the exact instant when I realized that a large part
msb at vex.net   |   of my life... was going to be spent in finding 
              |   mistakes in my own programs."     -- Maurice Wilkes

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