Seth Thomas ship's clock, strikes up to eight bells, every four hours.
Bells are rung evey half hour starting at 30 minutes after the hour: 12:30 is one bell, 1pm is 2 bells, until 4 pm is reached at 8 bells. The sequence is started again.
The half hour interval dates to when time was measured with a half hour sand or hour glass. The glass would be turned over every half an hour and a sailor would ring a bell which could be heard all over ship.
Watches change every four hours at eight bells.