The practice of ringing a bell as a way of keeping time began in the earliest days of sailing when sailors could not afford to buy a personal timekeeper. A system was created in which a bell was rung so that the crew would always know what time it was.
Navy Bell History
Before watches were affordable for the common sailor, the seaman on watch was given a half-hourglass to use to keep time. When the sand would run out of the half-hourglass, the watchman would ring the bell and turn over the glass once again, repeating the process throughout the day and night.
Ringing the Bell to Keep Time
Beginning at 12:30 a.m., the bell was rung every half-hour. The number of rings increases each half-hour and after four hours the process begins again with one ring at 4:30 a.m. In this way, sailors can also keep track of the time on board without having a watch.
Signaling a Watchman Change
Typically, the watchman kept watch for four-hour shifts, so ringing the bell eight times also signaled the change of watchmen. If the bell rang eight times without incident, the term became known as "eight bells and all's well." This practice of ringing bells is still intact, though more modern technology is utilized.