In the previous paper¹⁾ the authors reported some capsizing motions of a small craft in concentric transient waves with two successive crests in beam sea conditions. Large drift motions on the wave crests were observed, which seems to be characteristic of small crafts because of their light bodies and small drafts. As mentioned by Tanaka et al.²⁾ sway drag force can be significant in that large drifting motion because of the complicated under-water hull forms of small crafts. In this paper forced sway motion test was conducted. It is clarified that in a large amplitude sway motion drag component explains the main part of sway damping force, and that the moment coefficient due to the drag force varies widely according to heel angle. It is also clarified by a simulation program that the moment due to sway drag played a significant roll in the roll motion reported in the previous paper. This paper also deals with drag force and moment in a constant sway drift motion and in wind. The moment coefficient in a constant drift varies according not only to heel angle and but also to drift speed. As a result the heel angle is proportional to U³ in a free drift test in wind.