What defines a head-on situation between two vessels?

In a head-on situation, the defining factor is that the vessels see each other nearly ahead, and they can observe their respective masthead lights in line. This alignment indicates that both vessels are on a direct collision course. The interpretation of "head-on" is crucial for determining the responsibilities that each vessel has to avoid a collision.

This scenario establishes that each vessel is approaching the other from the front, which requires them to follow the regulations outlined in the COLREGs to take appropriate action to avoid a collision, typically by altering course to starboard. This is vital for maintaining safety at sea and ensuring that both vessels can pass safely.

Understanding this definition helps mariners recognize the importance of communication and navigation practices when encountering other vessels in close quarters, ultimately promoting safer maritime navigation. The other options describe situations that do not fit the parameters of a head-on encounter and would invoke different rules or navigational considerations.