Mast Light

The masthead light is a white light shining over a 225-degree arc, from right ahead to 22.5 degrees abaft each beam, mounted over the fore-and-aft centerline above the sidelights. Under COLREGs Rule 23 a power-driven vessel underway carries it; vessels of 50 m or more carry a second masthead light aft and higher, and the two in line show the heading and relative length at a distance. A sailing vessel under sail alone does not carry a masthead light, which is one way to tell sail from power at night.