Marine propulsion system dynamics during ship manoeuvres

Marine propulsion plants can experience large power fluctuations during tight manoeuvres. During these critical situations, dramatic increases of shaft torque are possible, up to and over 100% of the steady values in straight course. In the case of a twin-screw ship turning circle, the two shaft lines dynamics can be completely different in terms of required power and torque. This phenomenon, if not correctly considered, is potentially dangerous, especially for propulsion plants with two shaft lines powered via a unique reduction gear, which can be subject to significant unbalances. The paper presents a simulation approach able to represent the dynamics of a twin-screw ship propulsion plant in these critical working conditions. The numerical model includes the ship manoeuvrability and the dynamic behaviour of prime movers, shaft lines, propellers and propulsion control system. Numerical results obtained have been compared to full-scale measurements in order to validate the proposed simulation approach.