© 2021Screw propellers create asymmetry around the ship in motion, leading to differences in both side turnings despite the ship having symmetric hull form. A conventional rudder is not expected to contribute to it but a twisted rudder will generate additional asymmetry in the flow and may either balance or increase the difference in both side turnings. In this study, we try to understand the physics of appendage forces effecting the ship's maneuvering abilities. To fulfill this aim, we use the special benchmark case that has a twisted rudder; the Duisburg Test Case (DTC) Post-Panamax Container Ship. The study starts with showing that DTC does not have course-keeping ability. This will eventually lead to continuous turning, even at zero rudder angle, and it is proved by numerical simulations DTC leans to the starboard side during self-propulsion tests. Numerical simulations of turning circle motion shows that the ship has a smaller turning diameter towards the port direction. Flow visualizations reveal that the propeller opposes both side turnings but the degree of opposition to the starboard side is greater. Additionally, vortices generated at the pressure side of the rudder are more dominant in starboard turning leading to higher turning circle diameters towards the starboard side.