Two white lights and a green
Large vessel, crossing. Developing level, about 2 min. COLREGs Rules 21 & 23.
The situation
Night, good visibility. Fine on your port bow you see two white lights, the right one lower than the left, and a green light below them. Use the binoculars before you decide.
What are you looking at?
- A power-driven vessel of 50 m or more, showing her starboard side: Two masthead lights and a green sidelight.
- A power-driven vessel towing, seen from starboard: Two white lights and a green.
- A vessel under 50 m showing her port side: One masthead light and a sidelight.
Lookout: Two masthead lights reveal a larger vessel and her heading: the lower forward light and higher after light open apart as she turns across you.
The sound answer
A power-driven vessel of 50 m or more, showing her starboard side
Two staggered white masthead lights, the after one higher, mark a power-driven vessel of 50 m or more. Her green sidelight means you see her starboard side: she is crossing ahead of you from port to starboard.
Why the other options fall short
A power-driven vessel towing, seen from starboard
A towing vessel shows two or three masthead lights in a vertical line, one above the other, plus a yellow towing light above her sternlight. These white lights are separated fore and aft, not stacked.
A vessel under 50 m showing her port side
Green is always the starboard sidelight, and a vessel under 50 m need show only one masthead light. Two staggered masthead lights point to a larger vessel.
Rules 21 & 23 · Masthead lights and sidelights
A power-driven vessel of 50 m or more shows a forward masthead light and a second, higher masthead light abaft it, sidelights and a sternlight. The green sidelight shows on the starboard side from right ahead to 22.5° abaft the beam.