What defines a head-on situation between two vessels?

A head-on situation between two vessels is defined by the scenario where each vessel observes the other's masthead lights in line or nearly in line. This configuration indicates that the vessels are on a collision course, directly facing each other, leading to the need for action to avoid a collision.

In such cases, the visibility of the masthead lights from either vessel signals that they are effectively navigating towards one another, creating a critical requirement for adherence to navigational rules under the COLREGs. This situation obligates both vessels to take appropriate measures to alter course to prevent a collision, usually by each vessel altering to starboard.

Being able to see each other nearly ahead underscores the imminent risk of collision, distinguishing this scenario from situations where vessels are simply in proximity but not directly approaching each other head-on. Thus, the definition provided aligns with the principles outlined in the COLREGs, ensuring navigational safety by emphasizing the importance of communication and maneuvering in such circumstances.