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.
The classical system was:
| Number of bells | Middle watch | Morning watch | Forenoon watch | Afternoon watch | First dog watch | Last dog watch | First watch |
| One bell | 0:30 | 4:30 | 8:30 | 12:30 | 16:30 | 18:30 | 20:30 |
| Two bells | 1:00 | 5:00 | 9:00 | 13:00 | 17:00 | 19:00 | 21:00 |
| Three bells | 1:30 | 5:30 | 9:30 | 13:30 | 17:30 | 19:30 | 21:30 |
| Four bells | 2:00 | 6:00 | 10:00 | 14:00 | 18:00 | 22:00 | |
| Five bells | 2:30 | 6:30 | 10:30 | 14:30 | 22:30 | ||
| Six bells | 3:00 | 7:00 | 11:00 | 15:00 | 23:00 | ||
| Seven bells | 3:30 | 7:30 | 11:30 | 15:30 | 23:30 | ||
| Eight bells | 4:00 | 8:00 | 12:00 | 16:00 | 20:00 | 0:00 |
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 domestic "ship's bell" clocks use a simpler system:
| Number of bells | Hour (a.m. and p.m.) | ||
| One bell | 12:30 | 4:30 | 8:30 |
| Two bells | 1:00 | 5:00 | 9:00 |
| Three bells | 1:30 | 5:30 | 9:30 |
| Four bells | 2:00 | 6:00 | 10:00 |
| Five bells | 2:30 | 6:30 | 10:30 |
| Six bells | 3:00 | 7:00 | 11:00 |
| Seven bells | 3:30 | 7:30 | 11:30 |
| Eight bells | 4:00 | 8:00 | 12:00 |
The number of bells may be used to refer to the hour so indicated.
