Sea day

Sea day is an outdated international unit of time used by both military and civilian sailors until the middle of the 19th century (sometimes even later).

Sea days differed from ordinary calendar days in that they did not begin at midnight , like calendar, but at noon . It was from noon that a daily countdown was carried out on the ship with the help of bottles . Thus, marine, or navigational ( English nautical), time counting was different from civilian time. For example, 6 AM Monday civil time corresponded to 6 AM for the navigator on the navigational time count, and 6 PM Monday civil time corresponded to 6 AM, but already Tuesday. This led to great misunderstandings, since when the ship returned to the harbor, the navigator (and the logbook ) had to switch to civilian time ^[1] . However, the astronomical time count was also used in the fleet, since it was adhered to by the Sea Almanac used in navigation. The astronomical day also began at noon, as well as the navigation day, but were shifted by 1 day. All this could lead to errors.

In the Royal Navy of Great Britain, sea ​​days were canceled by a special instruction of the British Admiralty of October 11, 1805 , offering a new type of logbook , which ordered all royal ships to use a calendar, or civilian, day starting at midnight ^[1] . Since the 1820s, the British East India Company also refused to calculate time on sea days.