Effect of bilge keels on maneuverability of a fine ship

This paper discusses the effect of bilge keels on maneuverability of a fine ship experimentally and theoretically. To capture the effect, first, free-running model tests were conducted using a KCS container ship model with detachable bilge keels. We found that bilge keels improve the turning performance and enlarge overshoot angles in zig-zag maneuvers, and that this tendency becomes more pronounced with increasing ship speed. Next, captive model tests were conducted to capture the hydrodynamic forces' effects on maneuvering to clarify the reason for the difference in maneuvering in the presence of bilge keels. By attaching bilge keels, the absolute values of , , and (the linear derivatives of lateral force, yaw moment, and roll moment acting on the ship with respect to lateral velocity v, respectively) are increased and (the derivative of the lateral force with respect to roll ) is also increased. It can be explained theoretically that the change of the hydrodynamic derivatives leads to course instability according to the course stability criterion presented by Yasukawa and Yoshimura [3]. The special feature of the criterion is to include the roll-coupling effect. Thus, the roll-coupling significantly affects ship maneuverability through hydrodynamic derivative changes by attaching bilge keels to fine ships with small metacentric height (GM) over bar.