Abstract
Many researches have been done about the effect of a steering motion on roll motion, as the turning motion sometimes introduces a capsizing of ship and makes serious disasters. On the contrary, the researches of the effect of a roll motion on the manoeuvrability are very few, and the mechanism is not clear. In 1970s after the construction of a high-speed container ship, it began to be pointed out that the navigation difficulty arises with such ships, and then the research on the latter was started. Eda1), Hirano2) and Sohn3)respectively proposed the mathematical models of manoeuvring motion including the roll motion, and pointed out that the course-keeping ability becomes worse and the turning radius becomes smaller when ship speed increases. This tendency becomes remarkable with lower GM. In these researches, although the turning motions were well simulated using each mathematical model,the mechanism or structure of the roll effect on the manoeuvrability has not been clarified yet.In this paper, the author introduces the rudder to yaw response equation from the simple linear mathematical model, and has clarified the following principal structure regarding to the effect of the roll motion on ship manoeuvrability. 1) The turning moment Yφφ and Nφφ induced by the roll angle become the key parameter that strongly affects the course-keeping and turning abilities of ship. This tendency becomes remarkable when roll angle becomes larger by the lower GM and higher Froude number.2) For a high-speed merchant ship whose (N'φ -Y'φl'β) becomes larger in negative due to the large bulbous bow for example, the larger negative (N'φ -Y'φl'β) makes the less stability on course and the stronger turning ability, which may make the smaller turning radius and the larger overshoot angle in Z-manoeuvre.3) On the other hand, when (N'φ -Y'φl'β) is a positive value, it becomes a phenomenon completely contrary to the above.
