The Effect of Azimuth Thruster on the Manoeuvring Ability of a Stern Trawler in Rough Weather Conditions

The results of computational analyses on the manoeuvring performance of a stern trawler with an azimuth thruster located in the forward part of the vessel are presented. The initial design of the vessel with a single shaft, propeller and rudder is considered to have insufficient manoeuvring performance with a trawl pull load of 40 tons in moderate environmental conditions with a forward speed of 3 knots. The modified design is equipped with an azimuth thruster located in the forward part of the vessel that can rotate 360 degrees to produce additional thrust. In order to assess and simulate the manoeuvring performance of the vessel, the surge, sway and yaw equations are set and solved in the time domain. The hydrodynamic forces due to surge and sway motions and the yaw moment are represented by a nonlinear modular mathematical model. The manoeuvring coefficients of the mathematical model employed are estimated by two distinct approaches; the first one is based on semi-empirical methods and the other is based on computational fluid dynamics (CFD). The external forces due to wind, current and waves are mathematically represented by proven semi-empirical methods based on the results of scaled model tests and full-scale measurements. A comprehensive computational test matrix is established and extensive computational analyses and manoeuvring simulations were carried out to indicate that an azimuth thruster with sufficient thrust located in the forward part of a stern trawler could significantly improve the manoeuvring performance of the vessel despite adverse environmental conditions.