Question 56 OSV01 - Master/Chief Mate - Offshore Supply Vessels

The Correct Answer is A **Explanation for Option A (Shifting weights to the stern):** Shifting weights to the stern (or pumping out tanks forward and pressing them aft) increases the vessel's longitudinal radius of gyration ($K_L$). Increasing $K_L$ increases the vessel's longitudinal inertia. A higher longitudinal inertia means the vessel resists changes to its heading more effectively. Yawing in a following sea is primarily caused by the stern being lifted by a wave crest, allowing the hull to swing easily. By increasing the inertia resisting this swing, the amplitude and speed of the yawing motion are reduced, stabilizing the vessel's course. This effect is often described as making the ship "heavier on the ends." **Why the other options are incorrect:** * **Option B (Pumping out tanks aft):** Pumping out tanks aft shifts weight forward, which decreases the longitudinal radius of gyration ($K_L$). This reduces the vessel's longitudinal inertia, making the vessel less stable directionally and more prone to yawing and broaching in a following sea. * **Option C (Increasing GM):** GM (metacentric height) is a measure of transverse stability. While important for rolling and capsize resistance, GM primarily affects transverse stability and rolling period, not the vessel's resistance to yawing in a following sea (which is a longitudinal/directional stability problem). Increasing GM might even lead to a quicker, more uncomfortable roll, but it does not directly reduce yawing motion. * **Option D (Shifting weights to the bow):** Similar to Option B, shifting weights to the bow centralizes the mass, reducing the longitudinal radius of gyration ($K_L$) and longitudinal inertia. This makes the vessel directionally unstable and increases the tendency to yaw or broach when wave action affects the rudder effectiveness.