Question 66 OSV02 - Mate - Offshore Supply Vessels

The Correct Answer is A ### Explanation for A (Excessive rolling) When the period of the external force (the beam seas, meaning waves approaching from the side) is equal to the natural period of oscillation of the vessel (specifically, its natural rolling period), the condition known as **resonance** occurs. Resonance is a fundamental principle in physics where an external force applied at the natural frequency of a system causes the amplitude of the system's oscillations to increase dramatically. Since the external force is applied as beam seas (from the side) and matches the vessel's natural period for side-to-side motion (rolling), the energy input with each wave crest/trough reinforces the previous roll, leading to a rapid buildup of the rolling angle, resulting in **excessive rolling**. This phenomenon is extremely dangerous and can lead to cargo shifting or capsizing. ### Why other options are incorrect: **B) Excessive pitching:** Pitching is the motion of the bow and stern moving up and down (fore and aft oscillation). This motion is primarily excited by head seas (waves coming from directly ahead) or following seas (waves coming directly behind). Beam seas primarily excite rolling, not pitching. **C) Excessive yawing:** Yawing is the side-to-side rotation of the vessel around its vertical axis (deviation from the intended course). While excessive rolling can sometimes lead to minor yawing effects, yawing is primarily related to steering control, rudder action, or waves acting on the vessel's length, not the direct effect of beam seas matching the natural rolling period. **D) No change should be evident:** The matching of the wave period with the vessel's natural period is the definition of resonance, which by its nature causes the largest possible change in amplitude. Therefore, a significant change (excessive motion) is the most likely outcome, making "no change" incorrect.