What does "22.5 degrees abaft her beam" indicate about the overtaking vessel's position?

The phrase "22.5 degrees abaft her beam" describes the position of the overtaking vessel relative to the vessel being overtaken. When an overtaking vessel is said to be at this angle, it signifies that the overtaking vessel is approaching from behind and to the side of the vessel being overtaken.

When a vessel is located at 22.5 degrees abaft the beam, it is positioned in such a way that the vessel being overtaken is unable to show its sidelights to the overtaking vessel. Instead, the overtaking vessel will primarily see the sternlight of the vessel being overtaken. This is crucial for understanding the navigation rules, as it indicates the overtaking scenario and the responsibilities that come with it.

Understanding this positioning and the visibility of the lights helps in determining the traffic situation on the water and adhering to the COLREGs, especially when it comes to safe navigation and avoiding collisions.