Two masthead lights arranged vertically indicate which situation?

• A. A vessel at anchor
• B. A vessel not under command
• C. A vessel underway and making way
• D. A vessel towing another astern (tow less than 200 m)

Answer: (D)

Two white masthead lights stacked in a vertical line signal a towing arrangement. When a vessel is towing another astern and the tow length is under 200 meters, the towing vessel displays two masthead lights in alignment one above the other. This distinctive vertical pairing lets other mariners recognize that there is a tow behind, and it helps gauge how the vessel will maneuver with the attached tow. If the tow were longer, the lighting pattern would differ, reflecting the extended tow, but for a short tow the two vertical masthead lights are the standard indication.