Watch (or Duty) Sections. Watch standers are assigned to watch/duty sections. Each section has duty for a length of time, which may be a number of hours or one or more days. The number of sections and the number of watch standers in each section depends upon the number of watches that must be stood and the number of qualified personnel available to stand the watches. The highest number of duty sections is usually 6; the lowest is 2; and 3 is the usual number.
Watch Duration. The duration of watches will vary between commands due to the needs of the commands; however, the usual duration of a watch is four hours stating at 0400. In the traditional watch system, leftover from the days of sail, the ships company is divided into three sections and the day divided into six watches, each of four hours duration. Each day, a watch stander would stand a four-hour watch followed by eight hours off, followed by a four-hour watch, etc. During the times off watch, the sailor would work at normal job duties, eat, have some recreation time, and sleep.
Dogging the Watch. Normally a watch is 4 hours long, which creates 6 watches per day, which is an even number of watches. With an even number of watches, a watch section would be standing the same watches every day, such as the mid-watch. To eliminate this, the 1600-2000 watch is split into two 2-hour watches to create a 7th watch; this process is called dogging the watch. Each of these two split watches is called a dogwatch. Another reason for splitting this watch is that both watches will be able to eat the evening meal during normal meal hours.
The term dogwatch is said to derive from Sirius, the "Dog Star” because Sirius is the first star to come into view on the first dog watch. However, the time of the rising of Sirius varies with the time of year, so for much of the year Sirus is below the horizon at sunset. Additionally, since the first dogwatch (1600–1800) is typically stood during daylight, the stars are not visible. Another derivation is that someone standing one of these 'half' watches was said to be “dodging the watch,” so the watch was named the “dodge watch,” which was shortened to dogwatch