What does two masthead lights in a vertical line typically indicate?

Two masthead lights arranged in a vertical line typically indicates a long tow. In maritime navigation, the display of lights on vessels is crucial for identifying their status and operations. When you see two masthead lights, it signals that the vessel is towing another vessel, which can significantly affect its handling and maneuverability.

The regulation regarding masthead lights specifies that when a vessel is engaged in towing that is more than 200 meters in length, it should show two masthead lights in a vertical line. This arrangement allows other vessels to recognize the potential hazards associated with long tows and gives advance warning of the towing vessel's capabilities.

Understanding this signaling system is vital for maintaining safety on the water, as it helps to prevent collisions by informing other mariners of a vessel's operational condition.