bell used as early as the 15th century to sound the time on board ship by striking each half hour of a watch. The mariner's day is divided into six watches, each four hours long, except that the 4:00 to 8:00 PM watch may be “dogged”; that is, divided into the first and second dogwatches, each two hours long, to allow men on duty to have their evening meal. Through the 18th century, time was ordinarily measured on board ship by using a 30-minute sandglass. The quartermaster or ship's boy turned the glass when the sand ran through, and it became customary for him to strike the bell as he did so. Eight times in each watch the glass was turned and the number of strokes on the bell indicated the number of half hours elapsed after the men came on deck. These strokes are sounded in pairs, with an interval following each pair.

The place of origin of this seagoing custom is unknown, but it was nearly universal among Europeans and sailors of the Mediterranean area by the 18th century.

British ships, after the mutiny at the Nore (1797), followed a special numbering in the dogwatch. From 4:00 to 8:00 PM, the usual bells are struck except that at 6:30 PM only one bell is struck instead of five; two at 7:00 PM; three at 7:30 PM; and eight bells at 8:00 PM. Thus the signal for the mutiny, five bells in the second dogwatch, has never since been given.

A series of rapid, successive strokes on the bell is used as a warning during fog, and, at other times, this is a fire signal.