A posture control system for a hull includes trim tab main bodies as posture control plates attached to a stern of the hull to control the posture of the hull. Trim tab actuators drive the trim tab main bodies. Engines generate a propulsive force on the hull. A controller controls the trim tab actuators. Based on a throttle opening angle of the engines, the controller determines a time when the trim tab main bodies are to be lowered by the trim tab actuators.