# Naval custom of thirteen months.

**URL:** <https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181>\
**Category:** Factual Questions\
**Created:** [April 21, 2004, 6:11am UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181 "2004-04-21T06:11:15Z")\
**Posts on this page:** 1\
**Page:** 2

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**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\
**Post date:** [April 21, 2004, 11:03pm UTC](https://boards.straightdope.com/t/naval-custom-of-thirteen-months/241181/21 "2004-04-21T23:03:40Z")

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The link that johncole provides does mention the “nautical day” as starting at noon but also says this was ended in 1805 and before 1805 it seems it was not clear or universal, rtaher it was used for log keeping only and was a source of confusion which is why it was ended.

> [@](#):
>
> There were thus in use in the Navy until 1805 three days: the nautical, the civil or natural, and the astronomical. The nautical day entered in the log as May 10 began at noon of May 9 of the civil reckoning, and P.M. thus came before A.M. On the other hand, the astronomical day of May 10 began at noon of May 10 by civil reckoning, and ran from 0h to 24h ending at noon on May 11. This was the time used in the Nautical Almanac, first published in 1767, and this was the time kept by Mr. Charles Green, the astronomer on Cook’s first voyage. Though it must have been in continual use in the navigation of the ship, it does not appear in the logs. But it must be borne in mind as a possible source of confusion.

So, yes, it seems from that cite that for an indetermined number of years before 1805 some or all British ships used a nautical date which started 12 hrs before the local civil date and they used both simultaneously which was a source of confusion. I do not think the custom was widespread in other countries or in merchant ships. What _was_ universally widespread in merchant and naval vessels, British and foreign, was the practice of reckoning the days run from local apparent noon to local apparent noon and of adjusting the begining of the afternoon watch.

Different customs were kept with regards to changing the date (date line) etc. It used to be that the Philippines was on the same side of the date line as south America because it was colonized by the Spanish from there so an English ship out of Hong Kong and a Spanish ship out of Manila would meet and reckon dates a day apart.

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