Editing Time zone (section)

== Nautical time zones ==
{{Main|Nautical time}}

Since the 1920s, a [[nautical time|nautical standard time]] system has been in operation for ships on the [[international waters|high seas]]. As an ideal form of the terrestrial time zone system, nautical time zones consist of [[gore (segment)|gores]] of 15° offset from GMT by a whole number of hours. A nautical date line follows the 180th meridian, bisecting one 15° gore into two 7.5° gores that differ from GMT by ±12 hours.<ref>{{cite book |last=Bowditch |first=Nathaniel |title=American Practical Navigator |location=Washington |publisher=Government Printing Office |orig-date=1925 |date=1975}}</ref><ref>{{cite book |last1=Hill |first1=John C. |author2=Thomas F. Utegaard |author3=Gerard Riordan |title=Dutton's Navigation and Piloting |location=Annapolis |publisher=[[United States Naval Institute]] |date=1958}}</ref><ref>{{cite book |last=Howse |first=Derek |title=Greenwich Time and the Discovery of the Longitude |location=Oxford |publisher=Oxford University Press |date=1980 |isbn=0-19-215948-8}}</ref>

However, in practice each ship may choose what time to observe at each location. Ships may decide to adjust their clocks at a convenient time, usually at night, not exactly when they cross a certain longitude.<ref>{{cite web |url=https://www.cruisecritic.com/articles/what-is-cruise-ship-time |title=What Is Cruise Ship Time? Cruise Critic |date=January 7, 2020}}</ref> Some ships simply remain on the time of the departing port during the whole trip.<ref>{{cite web |url=https://caribbeanadventuresroatan.com/frequently-asked-questions/ |title=Frequently Asked Questions |archive-url=https://web.archive.org/web/20210214083749/https://caribbeanadventuresroatan.com/frequently-asked-questions/ |archive-date=February 14, 2021 |url-status=live |website=Caribbean Adventures Roatan}}</ref>