Recently, as environmental standards for ships have become harder like EEDI, and ship speed became slower, securing of maneuverability of a ship in low speed operation becomes to be an important issue. As well known, marine rudders play the most important role in ship maneuvering and navigating. High lift performance rudders such as fishtail rudders and flap rudders have been widely used for smaller ships in order to improve their maneuvering and navigating in ports and docking. For larger ships such high performance rudders should be developed too. The rudders should be optimized in order not only to maneuver the ship safely, but also to improve the efficiency of her propulsion. In this book, a CFD commercial code, ANSYS FLUENT, is used to investigate the hydrodynamics performance of the high lift rudders such as fishtail and wedge tail rudders to understand the mechanism of increasing of the lift and drag forces. A smaller rudder with the same lift performance as a conventionalrudder is developed by using the CFD.