BOTH INTERNATIONAL & INLAND Which light configuration may a sailing vessel exhibit while underway?

Correct Answer: Option C — a red light over a green light at the masthead

Rule 25(c) permits a sailing vessel underway to exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower green. These are in addition to the required sidelights and stern light.