What do three white lights signal on a vessel?

The presence of three white lights on a vessel is a specific signal indicating that the vessel is engaged in a long tow. According to maritime navigation rules, vessels involved in towing operations use a specific configuration of lights to inform other mariners about their activities and the nature of their tow.

When a vessel is towing, particularly if it is a significant distance or weight, it is required to display these three white lights in a vertical arrangement. This signal serves to alert other vessels of the potential hazards associated with the towing operation, indicating that the tow may restrict the vessel's maneuverability and the tow-line may pose risks for nearby vessels. Understanding these lighting configurations is crucial for safe navigation and ensuring that all mariners are aware of the status and intentions of other vessels, particularly in busy waterways.

In contrast, the other options relate to different maritime signals that are not represented by three white lights, making it essential for mariners to recognize these indications accurately to navigate safely.