Accurate estimation of added resistance in waves is very important for evaluation of ship performance in actual seas. However, most estimation methods do not treat the influence of roll motion on added resistance in waves.

In this paper, a practical correction method for added resistance considering the influence of roll motion is proposed, and the proposed method is investigated by tank tests. In this estimation method, the roll component is extracted from the equation for added resistance in waves in accordance with the concept of Gerritsma & Beukelman's method. This study demonstrated that adding the roll component to the estimation equations improves the accuracy of estimations of added resistance in oblique waves. A sensitivity analysis was also performed using the proposed method in order to discuss the effect of roll motion on fuel consumption in actual seas.