In this paper，the stable heel angle and the hydrodynamic performance(rudder side force)of SWATH during full rudder rotation are the research objects. Based on CFD calculations，the influence analysis of different rudder area ratios on the rotary heel angle and the power of the steering gear is carried out. The two working conditions with rudder area ratio of 3.0% and 4.0% are evaluated separately，and anauzed in combination with the general rules and methods of rudder design，which can provide reference and basis for the design of SWATH rudder area.
