You see both red and green sidelights and three white lights in a vertical line at night. What does this indicate about the vessel?

The sighting of both red and green sidelights along with three white lights in a vertical line suggests that the vessel is engaged in towing operations, specifically towing a tow that measures more than 200 meters in length. According to the Rules of the Road, vessels that are towing must display a specific light configuration to indicate their activity to other vessels.

The red and green sidelights denote the sides of the vessel, with red indicating the port side and green indicating the starboard side. The presence of three white lights arranged vertically typically signifies that the vessel is in a towing operation, with the additional lights indicating the length and potential hazard of the tow it is managing.

This arrangement fulfills regulatory requirements under the navigation rules, ensuring that other vessels are made aware of the towing operation and the increased risk associated due to the length of the tow. Therefore, this combination of lights serves as a clear signal about the vessel's role on the water at night, ensuring safe navigation and awareness among all vessels in the vicinity.