Investigation of the manoeuvrability characteristics of a Gate Rudder system using numerical, experimental, and full-scale techniques

The Gate Rudder is a recently introduced twin rudder system whose major advantages stem from its energy saving properties. The two foil-shaped blades of the rudder, placed aside of the propeller, act as a partial duct in the wake of the hull producing additional thrust. However, since the rudder is a primary safety device on any vessel, investigating the manoeuvrability performance of the Gate Rudder is a critical aspect that needs careful and detailed consideration. Owing to its peculiar working principle and location, the standard manoeuvrability prediction methods cannot produce reliable results since they are applied to r udders acting behind the propellers. This paper presents the first comprehensive investigation into the manoeuvrability performance of a Gate Rudder system, which includes the development of a modified MMG model, towing tank experiments and fullscale measurements. The modified MMG model was conceived to predict the manoeuvring motions of a ship with
the Gate Rudder system. A generalised prediction method is defined based on this modified MMG model and detailed CFD analysis of the flow pattern around the Gate Rudder for two commercial hull-forms. The simulation model of the Gate Rudder is validated by means of towing tank tests and full-scale manoeuvring trials. The sea trials were conducted onboard two sister container vessels, the first fitted with the first-ever Gate Rudder system and the second with a high-performance flap rudder. This also allowed to compare the two different steering
systems.