Turning ability analysis of a fully appended twin screw vessel by CFD. Part II: Single vs. twin rudder configuration

In the present paper, the analysis of the turning capability of the naval supply vessel presented in Part I (Broglia et al., 2015) is continued with different stern appendages, namely twin rudder and centreline skeg. The main purpose of the analysis is to assess the capability of an in-house CFD tool in capturing the different manoeuvring characteristics of the ship hulls; the test case is challenging, as the difference between the two configurations lies in the complex flow structure related to rudder-propeller interactions. Moreover, although the twin rudder solution slightly improves the poor course keeping ability of the original vessel, the course stability remains poor and, consequently, large lateral motions and drift angle have to be expected during the manoeuvre. The manoeuvring capabilities of the new configuration are discussed and compared with the single rudder configuration, focusing on the nature of the hydrodynamic forces and moments acting on the main hull and appendages during the transient and stabilized phases of the manoeuvre. Emphasis will be also given to the different contributions of the propulsion system in the twin rudder configuration, that results from the different rudder-propeller interaction.