 upright=1.3|A sailor keeps watch aboard .|alt= Watchkeeping or watchstanding is the assignment of sailors to specific roles on a ship to operate it continuously. These assignments, also known as at sea watches are constantly active as they are considered essential to the safe operation of the vessel , and also allow the ship to respond to emergencies and other situations quickly. These watches are divided into work periods to ensure that the roles are always occupied at all times, while those members of the crew who are assigned to a work during a watch are known as watch keepers . On a typical seafaring vessel, be it naval or merchant, personnel "keep  watch" in various locations and duties across the ship, such as the bridge and engine room. Typical bridge watchkeepers include a lookout and a deck officer who is responsible for the safe navigation of the ship; whereas in the engine room, an engine officer ensures that running machinery continues to operate within tolerances. Watch durations vary between vessels due to a number of reasons and restrictions; some watch systems aim to ensure that each team takes turns to work late at night, while other systems ensure the same team consistently works at the same hours every day. Aboard United States submarines, the crew is typically divided into three sections, with each section keeping 8 hours of watch followed by 16 hours off-watch. This schedule has been a fairly recent change to submariner work and rest routines. For nearly 45 years prior to 2015, submariners were on 18-hour days with 6 hours of watch followed by 12 hours off watch. The 12 hours off-watch were further divided into the first 6 hours being used for maintenance, cleaning, and entertainment; while the second 6 hours were usually for sleeping. A ship's bell is used in concert with a watch system to indicate the time by means of bell strikes to mark the time and help sailors know when to change watches. Unlike civil clock bells, the strikes of a ship's bell do not accord to the number of the hour. Instead, there are eight bells, one for each half-hour of a four-hour watch. Bells would be struck every half-hour, and in a pattern of pairs for easier counting, with any odd bells at the end of the sequence.
ʔ upright=1.3|A sailor keeps watch aboard .|alt= Watchkeeping or watchstanding is the assignment of sailors to specific roles on a ship to operate it continuously. These assignments, also known as at sea watches are constantly active as they are considered essential to the safe operation of the vessel and also allow the ship to respond to emergencies and other situations quickly. These watches are divided into work periods to ensure that the roles are always occupied at all times, while those members of the crew who are assigned to work during a watch are known as watchkeepers . On a typical seafaring vessel, be it naval or merchant, personnel "keep a watch" in various locations and duties across the ship, such as the bridge and engine room. Typical bridge watchkeepers include a lookout and a deck officer who is responsible for the safe navigation of the ship; whereas in the engine room, an engine officer ensures that running machinery continues to operate within tolerances. Watch durations vary between vessels due to some reasons and restrictions; some watch systems aim to ensure that each team takes turns to work late at night, while other systems ensure the same team consistently works at the same hours every day. Aboard United States submarines, the crew is typically divided into three sections, with each section keeping 8 hours of watch followed by 16 hours off-watch. This schedule has been a fairly recent change to submariner work and rest routines. For nearly 45 years before 2015, submariners were on 18-hour days with 6 hours of watch followed by 12 hours off watch. The 12 hours off-watch were further divided into the first 6 hours being used for maintenance, cleaning, and entertainment; while the second 6 hours were usually for sleeping. A ship's bell is used in concert with a watch system to indicate the time utilizing bell strikes to mark the time and help sailors know when to change watches. Unlike civil clock bells, the strikes of a ship's bell do not accord to the number of the hour. Instead, there are eight bells, one for each half-hour of a four-hour watch. Bells would be struck every half-hour, and in a pattern of pairs for easier counting, with any odd bells at the end of the sequence.
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