The Anglo-French Conference on Time-keeping at Sea was a conference held in

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in June 1917.

History

The Conference established the nautical date line and adopted an ideal form of the terrestrial

time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...

system for use at sea. It recommended that time changes required by changes of

longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...

be made in one-hour steps. This recommendation was adopted between 1920 and 1925 by all major fleets, including

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, French and American. The rules applied to almost all naval ships and to many non-naval ships. Nevertheless, up to the

Second World War World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

, the old practice of keeping local apparent time prevailed on many independent merchant ships.

Current usage

{{Main, Nautical time The nautical date line is implied but not explicitly drawn on time zone maps. It follows the 180° meridian except where it is interrupted by

territorial waters Territorial waters are informally an area of water where a sovereign state has jurisdiction, including internal waters, the territorial sea, the contiguous zone, the exclusive economic zone, and potentially the extended continental shelf ( ...

adjacent to land, forming gaps: it is a pole-to-pole dashed line. Ships are required to adopt the

standard time Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the r ...

of a country when they are within its territorial waters, but must revert to international time zones (15° wide pole-to-pole gores) as soon as they leave territorial waters. The 15° gore that is offset from GMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from GMT by ±12 hours. In reality nautical time zones are used only for radio communication etc. Internally on the ship, e.g. for work and meal hours, the ship may use a suitable time of its own choosing. This includes fixed installations such as oil rigs. For example, the Norwegian Ekofisk oil rigs are located in international water at longitude 3°E but use Norwegian time.

History

Current usage

See also