Two white lights, no colours
At anchor. Advanced level, about 2 min. COLREGs Rule 30.
The situation
Night. Ahead of you are two white lights, well apart horizontally. The left one is higher than the right. You can see no red or green light, and the bearing of both stays the same.
What are you looking at?
- A vessel of 50 m or more at anchor: A higher forward and a lower after anchor light.
- A large power-driven vessel underway, seen abeam: Two masthead lights.
- A vessel aground: Anchor lights.
Lookout: With no sidelight, ask whether she is moving at all. Then compare which white light is higher and where it is.
The sound answer
A vessel of 50 m or more at anchor
A vessel at anchor of 50 m or more shows an all-round white light forward and a second, lower one at or near the stern. The higher light marks her bow, here on the left.
Why the other options fall short
A large power-driven vessel underway, seen abeam
Underway, a large power-driven vessel shows her after masthead light higher than the forward one, and a sidelight is visible from abeam. Here there is no sidelight, and the forward light is the higher one.
A vessel aground
A vessel aground shows anchor lights plus two all-round red lights in a vertical line. No red lights are visible here.
Rule 30 · Anchored vessels and vessels aground
A vessel at anchor shows an all-round white light in the fore part and, if 50 m or more, a second lower one at or near the stern. A vessel aground adds two all-round red lights in a vertical line.