Dogwatch
A dogwatch is one of the two two-hour watches between 4 p.m. and 8 p.m. aboard ship, split so that no crew is stuck with the same night hours forever.
At six in the evening, on a ship under the old watch bill, the clock does something no landlubber’s clock ever does. It hands the same four hours to two different sets of people.
A dogwatch is one of two two-hour watches, 1600 to 1800 and 1800 to 2000, made by cutting the evening four-hour watch in half. Counting from midnight, the day holds the middle watch, the morning watch from 0400, the forenoon from 0800, the afternoon from 1200, the two dogs, and the first watch at 2000: seven watches, where plain four-hour blocks would give six.
The odd number does the work. Take a ship with two crews, port and starboard, trading watches in turn. With six equal watches, the port crew would stand watches one, three and five every day, and the starboard crew two, four and six. Whoever drew the middle watch, midnight to 0400, would draw it for the voyage. With seven, the pattern slips by one position at day’s end. The crew that had the afternoon yesterday has the forenoon today, and the midnight hours move to the other crew on alternate days. Worked through day by day, each crew takes the middle watch every second night.
Where the name comes from
The origin is uncertain; one proposed source is a similar German or Dutch term. A second explanation says men on the half watch were “dodging” the watch, and the word wore down to “dog.” A third reaches for Sirius, the Dog Star.
What it teaches ashore
A fixed schedule is easy to write and hard to bear, and a rotating one is the reverse. For the sleep data on a fixed three-on, nine-off pattern, see what a destroyer’s sailors recorded. The dogwatch is the older and simpler answer to the same problem: spread the worst hours around.