How many masthead lights are required when a 50-meter power-driven vessel is towing a tow that exceeds 200 meters?

In accordance with the COLREGs (International Regulations for Preventing Collisions at Sea), power-driven vessels that are towing must display additional lights to ensure they are clearly visible to other vessels, especially when towing operations exceed certain lengths.

For a power-driven vessel that is towing a tow exceeding 200 meters in length, the regulations specify that it should show three masthead lights in a vertical line. This is essential to communicate to other vessels that the tow is significantly long, which increases the risk of collision and requires greater situational awareness from nearby ships.

The first light indicates the power-driven vessel itself, the second light shows that it is engaged in towing, and the third light is displayed due to the length of the tow exceeding the requirement, providing an additional visual signal of the vessel's overall dimensions. Therefore, the correct answer is that three masthead lights are necessary in this particular scenario, ensuring compliance with safety regulations on the water.