Abstract
It is well known that the coupling effect of sway on roll of a ship at zero forward speed in beam seas is significant. The effect at forward speed, however, has not been clarified yet. In this study, the coupling effect of a ship at forward speed is experimentally investigated. Roll motions of a scale model of a training ship "Kagoshima maru" running in beam seas are measured in sway-fixed condition, and the results demonstrate that the roll amplitude increases with forward speed. It is common that the roll amplitude of a ship generally decreases with forward speed since the roll damping of it increases with forward speed. Therefore the phenomenon obtained in the measurements is different from the general characteristics of roll motion of a ship. To clarify the reasons, measurements of roll damping and wave exciting moment are carried out, and the lift component in the wave exciting moment is predicted. Then, it is revealed that this is partly because the lift component created by transverse velocity in beam seas increases the roll exciting moment, and partly because the roll damping of the ship used here does not increase with forward speed. The characteristics of the roll damping of the ship are also discussed.
