The manoeuvrability of ships in restricted water, particularly in narrow waterways, has been receiving a great deal of attention in recent years because of the ever-increasing size of ships such as tankers. This paper deals with the effect of finite water channel width on ship manoeuvrability and is a expansion of the author's previous paper for shallow water effects on ship manoeuvrability. It is calculated that the derivatives of the force acting on a rectangular plate which is to be combined motion in forced yawing technique in narrow, shallow waterways and in open, shallow waterways. From these results of calculation, it is presumed that the effect of finite water channel width on ship manoeuvrability. According to this results, it can be said that the ratio of derivatives in narrow waterways and in open waterways is relatively small compared to the shallow water effects. And the effect of finite water channel width is not affect in W/L ≥1.0