A watch system, watch schedule, or watch bill is a method of assigning regular periods of work duty aboard ships and some other areas of employment. A watch system allows the ship's crew to effectively operate the ship 24 hours a day for the duration of long voyages or operations.

Many watch systems incorporate the concept of dogging, whereby one watch is split into two shorter watches so that there is an odd number each day. Doing so allows crew members to have a different watch schedule each day. Often, the dog watches are set at dinner time to allow the entire crew to be fed in short order.

In the traditional Royal Navy watch system (a system used by most other Commonwealth navies), 'watch' refers to a period of time and to a grouping of personnel. Those members of the crew whose work must be done at all times of the day - known as 'watch-keepers' - are assigned to one of two watches: the Starboard or the Port watch. These can be further divided into two parts, e.g. First Port, Second Starboard. These two watches - or more usually the four parts of watches - alternate in working the following watches:

  • First watch: 20:00 to 00:00
  • Middle watch: 00:00 to 04:00
  • Morning watch: 04:00 to 08:00
  • Forenoon watch: 08:00 to 12:00
  • Afternoon watch: 12:00 to 16:00
  • First dog watch: 16:00 to 18:00
  • Last dog watch: 18:00 to 20:00

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