What does showing three masthead lights indicate about a tow?

Showing three masthead lights indicates that the vessel being towed exceeds 200 meters in length. This marking is part of the International Regulations for Preventing Collisions at Sea (COLREGs), which establish guidelines to promote navigational safety. According to these regulations, different configurations of masthead lights serve as visual signals to other vessels about the size and type of the vessel in question.

When a vessel displays three vertical masthead lights, it signals that the tow is long and demands specific attention from the crewmembers of other vessels. This configuration helps those on the water to identify the tow’s dimensions effectively and understand that it is larger than 200 meters. This is crucial, as vessels of such length impose unique navigational challenges and require appropriate caution when maneuvering in their vicinity.

The other options relate to different size classes for towed vessels but do not correspond with the requirements set for a vessel exceeding 200 meters, confirming the accuracy of the answer.