From sunset to sunrise, what navigational lights must be shown when a vessel is underway?

• A. Only a white stern light
• B. Sidelights (red on the port side, green on the starboard side) and a white running light; a white stern light if required.
• C. A blue masthead light
• D. Only fog lights

Answer: (B)

From sunset to sunrise, a vessel underway must display navigation lights that reveal its presence, heading, and movement to other mariners. The red light on the port side and the green light on the starboard side (sidelights) together with a white running light (forward) show that the vessel is moving and help others determine its direction. A white stern light is required if the vessel’s size or local rules call for it, completing the signaling from behind. This combination provides the essential, unambiguous signals needed to prevent collisions at night. Other options miss one or more of these standard signals or use lights that don’t convey the vessel’s underway status.