V-belt drive

A V-belt drive transmits power from a pulley on the engine to a driven pulley using one or more wedge-section belts that grip the V-groove by side friction, the wedge action multiplying the grip for a given tension. On auxiliary and emergency diesels it drives engine-mounted seawater and freshwater pumps, the charging alternator, and small fans. Belts are a wear and maintenance item: they stretch and need re-tensioning, slip and glaze when loose, and snap without warning, which can stop cooling-water flow and overheat the engine. Class rules generally bar single-belt drives for essential services, requiring multiple belts so the loss of one does not stop the pump.