What does Rule 30 specify about vessel communication?

Answer: C — Vessels must signal their intentions

Rule 30 of the COLREGs addresses the communication of intentions between vessels to avoid collisions and ensure safe navigation. It emphasizes that vessels must signal their intentions when the circumstances require it. This may include using sound signals or other appropriate measures to communicate their planned actions, such as maneuvers or changes in course. The requirement for vessels to signal their intentions is critical for effective navigation in congested waters or situations where visibility may be limited, as it helps prevent misunderstandings that could lead to dangerous encounters. It reinforces the importance of clear communication in maritime operations. Other options do not align with the provisions of Rule 30. Communication is not limited to commercial vessels or restricted to visual signals, and sound signals are permissible regardless of the time of day, so those do not accurately represent the specifications set out in Rule 30.