Watch 13 : The day at sea is divided into six four hour periods. Three groups of watchstanders are on duty for four hours and then off for eight, then back to duty. Seamen often work overtime during their off time. (Maritime)
EESiFlo North America, Terminology and Glossary: Maritime Terms, Pennsylvania, USA 2002, flowmeterdirectory.com/flowmeter_terminology. (Mrtm/ Ports and Ships - Amer) {539}