BOTH INTERNATIONAL & INLAND At night you sight a vessel displaying a single green light. Which vessel have you sighted?

Correct Answer: Option C — a sailing vessel underway

Rule 25(a) states that a sailing vessel underway shall exhibit sidelights and a stern light. However, Rule 25(c) allows a sailing vessel of less than 20 meters to combine these into a single lantern at or near the top of the mast, appearing as a single green light.