The History of Ship Clock Chimes Mariners have used a unique bell code to tell time at sea for hundreds of years. The code is based on the crew’s typical workday routine while the vessel is underway. A ship at sea requires constant attention throughout the day’s 24 hours. Therefore, the day is divided into six four-hour periods that are each called a “watch.” Similarly, the crew is broken up into three divisions. Division members stand their individually assigned duties on two watches per day, with eight hours off duty between watches.