Measure time onboard ship. One bell sounds for each half hour. One bell means 12:30, two bells mean 1:00, three bells mean 1:30, and so on until 4:00 (eight bells). At 4:30 the cycle begins again with one bell
US Department of Transportation, Maritime Administration, Glossary of Shipping Terms, Washington, DC, USA 2008. http://www.marad.dot.gov/documents/Glossary_final. pdf, (Mrtm - Amer) {572}