Turning and zig-zag maneuvers of ships with large block coefficients under full- and ballast-load conditions

This study investigates the differences in ship maneuverability between full- and ballast-load conditions using systematic tank tests. First, free-running tests were conducted to capture turning and zig-zag maneuvers under both load conditions using three ship models with different block coefficients ( C b ). Turning indices (advance, tactical diameter) are smaller under full-load conditions than under ballast-load conditions. Consequently, if the turning indices under ballast-load conditions satisfy the International Maritime Organization (IMO) rules, compliance is automatically ensured under full-load conditions. In contrast, the overshoot angles (OSAs) of zig-zag maneuvers under full-load conditions are approximately two to three times larger than those under ballast-load conditions. Therefore, even if the OSAs under ballast-load conditions satisfy the IMO rules, compliance with the IMO rules under full-load conditions is not necessarily ensured. In fact, the OSA of the ship with C b = 0 . 87 under the full-load condition was only at the limit of the IMO rules. Subsequently, captive model tests were conducted to grasp the hydrodynamic force characteristics during maneuvering using the same ship models. The difference in maneuverability between the full- and ballast-load conditions is attributed primarily to the difference in the derivative N G v ′ , which represents the yaw moment derivative with respect to lateral velocity. The absolute value of N G v ′ under full-load conditions was approximately twice that under ballast-load conditions, causing the fully loaded ship to move toward course instability. Thus, turning performance improves, whereas OSAs increase significantly and zig-zag maneuvering performance deteriorates. • Investigated ship maneuverability between full-load, FL and ballast-load, BL. • Conducted free-running tests using three models with different block coefficients. • If turning indices in BL satisfy the IMO rule, compliance is ensured in FL. • Even if OSAs in BL satisfy the rule, compliance is not necessarily ensured in FL. • The OSAs in FL are approximately two to three times larger than those in BL.