Equivalent standard manoeuvres for pod-driven ships

Abstract

Procedures for carrying out the manoeuvring tests presented in International Maritime Organisation (IMO) resolution MSC.137(76) are based on the capabilities of ships with conventional steering-propulsion systems. Therefore they do not correspond to ships with other steering-propulsion devices, like pod drives. IMO is aware of this shortcoming and for ships with non-conventional steering and propulsion system may permit the use of comparative steering angles to the rudder angles specified by the resolution. To elaborate these comparative angles for pod-driven gas carrier, experiments with free-sailing manned model have been carried out. For comparison two sister ships have been taken into consideration, i.e. twin-pod and twin-propeller twin-rudder configurations. For both ship versions, manoeuvres according to standard IMO procedures have been carried out. For twin-pod configuration, additionally manoeuvres with various pod propulsor settings have been performed to find the comparative, i.e. rudder-equivalent pod propulsor angles. Results show an obvious fact, that for twin-pod ship version similar results of standard manoeuvre parameters, as for twin-propeller twin-rudder version, are obtained for other than IMO recommended 35° steering angle. It is shown that, for turning circle parameters, a single comparative or rudder-equivalent angle does not exist. Various turning circle parameters are obtained for different pod propulsor angles.