Common failures of ship propulsion shafts

This article aims to provide a critical review of the most common failures of ship propulsion systems as a crucial ship system, with emphasis on fatigue failure. The accent is given on the shaft of marine propulsion systems as a most common point of failures in the entire propulsion system. A general description of failure causes and failure analysis methodology is presented. Several representative case studies summaries for fatigue failure on critical points of the propulsion shaft are described. Torsional vibrations and geometric stress concentrations of the shaft are identified as the most common cause of fatigue failure. The importance of constant monitoring, measurement and data collection of fatigue indicators and indicative events that have influence on fatigue development is emphasized. Methods used in failure analysis are discussed and propositions for improvement are given, especially in terms of using numerical routines in failure prediction.