What do vessels of 50 meters display in addition to their sidelights and a stern light?

Vessels that are 50 meters in length or longer are required to display a masthead light in addition to their sidelights and stern light. The masthead light is typically positioned at the fore part of the vessel and is visible over an arc of 225 degrees, enabling other vessels to determine the direction the larger vessel is facing. This lighting requirement is intended to enhance visibility and navigation safety, particularly in conditions with limited sight.

The other options provided, such as two aft lights or additional sidelights, are not specified requirements under navigation rules for vessels of this size. The correct lighting configuration helps ensure that vessels can be identified by other mariners, which is crucial for safe navigation, particularly during nighttime or poor visibility conditions.