Ship's bells are a system to indicate the hour by means of bells, used aboard a ship to regulate the sailors' duty watches.

Unlike civil clock bells, the strikes of the 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.

The classical system was:

Ship bell of ORP Iskra II - Polish Navy school tall ship

Most of the crew of a ship would be divided up into between two and four groups called watches. Each watch would take its turn with the essential activities of manning the helm, navigating, trimming sails, and keeping a lookout.

The hours between 16:00 and 20:00 are so arranged because that watch (the "dog watch", which is cur-tailed) was divided into two. The odd number of watches aimed to give each man a different watch each day.

Some "ship's bell" clocks use a simpler system:

The number of bells may be used to refer to the hour so indicated. de:Schiffsglocke