Effect of High-Aspect-Ratio Appendages on the Steady-State Balance of a Primary Wind-Powered Containership

Adding a Wind Propulsion System (WPS) to a merchant ship generates an added resistance due to the additional aerodynamic side force. It is called sail-induced resistance. A large sail-induced resistance reduces the net thrust provided by the WPS and also indicates that the ship is sailing with large leeway angle and rudder angle, the latter being detrimental to the ship’s manoeuvrability. To mitigate these effects, it is possible to add appendages beneath the hull, in order to increase the hydrodynamic side force and thus reduce sail-induced resistance and rudder angle. However, such appendages also increase the friction resistance. A challenge is then to make sure that the reduction in sail-induced resistance more than compensates the increase in total resistance. This study compares three types of high-aspect-ratio appendages for a 100-m-long containership sailing at 10 kn. The hull form is based on that of the KCS vessel. The appendages are: (i) a passive high-aspect- ratio vertical keel; (ii) the same keel with an optimised angle of attack; and (iii) an extended rudder. The approach is based on low-fidelity numerical models of the ship and appendages that have been implemented in a ship simulator. The effect of the WPS on the ship is modelled solely as an aerodynamic side force. Results indicate that the active keel and the extended rudder are similarly relevant to reduce sail-induced resistance and rudder angle. In contrast, the reduction in sail-induced resistance and rudder angle is much more limited with the passive keel. Moreover, it is shown that for ships with a low metacentric height, such as containerships, being primary wind-powered can be a challenge with respect to heel angle. Keywords wind propulsion; sail-induced resistance; 4-DOF MMG; KCS; high-aspect-ratio appendages