Which situation exemplifies a vessel that is unable to maneuver?

A vessel that is unable to maneuver is one that cannot take the necessary actions to avoid collision or navigate safely due to operational limitations. When a vessel loses its engine, it loses the propulsion needed to steer and control its movement, effectively rendering it unable to maneuver effectively. This situation creates a significant risk of collision and requires other vessels to take precautions according to the navigation rules, which classify the vessel as "not under command."

In contrast, restricted visibility may hinder a vessel's ability to detect hazards but does not inherently prevent it from maneuvering. A vessel that is making way and is underway indicates that it is actively moving, demonstrating that it has the capability to maneuver as needed. Thus, loss of engine power is the clear situation that illustrates a vessel being unable to maneuver.