Telling time by the ship's bell has a romantic background that goes back hundreds of years.  It is based on the workday routine of the ship's crew.  A ship at sea requires a constant watch throughout the whole 24 hours of the day.  To divide duty, the day is broken up into six watches of four hours each, and the crew into three divisions or watches.  Each division of the crew stands two four hour watches a day.  In order to rotate the duty, so that a division does not have the same watch day in and out, the 4 to 8 watch in the afternoon is divided into two watches known as dog watches.  Here's how they are set up:

The First Watch                 8 PM. to Midnight.
The Mid-Watch                 Midnight to 4 AM.
The Morning Watch           4 AM. to 8 AM.
The Forenoon Watch         8 AM. to 12 Noon.
The Afternoon Watch        12 Noon to 4 PM.
The Frst Dog Watch          4 PM. to 6 PM.
The Second Dog Watch     6 PM. to 8 PM.

To apprise the crew of the time, the ship's bell was struck by the watch officer at half hour intervals.  By this method of time keeping eight bells mark 4, 8, and 12 o'clock..

Ship's Bell Code

Eight bells       12:00              4:00                8:00

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 denotes time to relieve the watch.
Hours -- even numbers
Half hours -- Odd numbers

With a ship's bell clock.  You can hear the time.  You do not need to see it.

From: Chelsea Clock Company, Chelsea, Massachusetts