Which lights are required for a barge, not part of a composite unit, being pushed ahead?

A barge that is not part of a composite unit and is being pushed ahead is required to display sidelights and a special flashing light. This configuration is important for ensuring visibility and identifying the vessel's status and activity to other mariners.

The sidelights, which are red and green, indicate the barge's port and starboard sides, allowing other vessels to understand its direction and orientation. The addition of a special flashing light serves as a warning to other vessels, particularly in reducing visibility conditions or congested waterways, making the barge more detectable.

The other options do not meet the regulatory requirements of the International Regulations for Preventing Collisions at Sea (COLREGs) for a barge being pushed ahead. For instance, only a masthead light or two all-round white lights do not provide the necessary indication of both the vessel's identity and direction, thus lacking adequate navigation safety. Sidelights and stern lights alone also fail to deliver adequate information about the vessel's operation in line with the collision regulations. Therefore, the necessity for sidelights combined with a special flashing light enforces a higher standard of communication on the water, ensuring both safety and navigational clarity.