A prediction program of manoeuvrability for a ship with a gate rudder system

Carchen, Alessandro and Shi, Weichao and Sasaki, Noriyuki and Atlar, Mehmet; Sariöz, Kadir and Solak, Hayriye Pehlivan, eds. (2016) A prediction program of manoeuvrability for a ship with a gate rudder system. In: 2nd International Meeting - Recent Advances in Prediction Techniques for Safe Manoeuvring of Ships and Submarines. Istanbul Technical University, TUR.

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The Gate Rudder is a special twin rudder system with two rudder blades placed aside of a propeller. Main advantage of this system is the energy saving originated from the rudder thrust which is induced by the two cambered rudder blades comparably efficient to ducted propellers. However, as any rudder’s prime task, the performance of manoeuvrability is critical to the Gate Rudder too. With the currently available Manoeuvring Modelling Group (MMG) simulation programs, the simulation is only applicable to the traditional single rudder located behind the propeller. Therefore, how to predict the manoeuvring performance for the gate rudder is the focus of this paper. On the other hand, a recent study of the Gate Rudder reveals that this innovative system has remarkable flap effect which is well known as a manoeuvring interaction between rudder blades and ship stern. This phenomenon has been observed in the case of conventional rudder and introduced into an MMG-based theoretical model as interaction factor aH. However, the average values of aH for conventional rudder is between 0.1-0.2 in general whilst the aH value for the Gate Rudder is more than twice as much, showing a superior course keeping ability of the Gate Rudder. The paper presents the manoeuvrability simulation method of a ship with this Gate Rudder system and introduces some examples of comparisons between the model tests and free running tests which was conducted with 2.5 m ship model in the manoeuvring tank at Kyushu University, Japan.