Final answer:
A vessel being pushed ahead that is not a composite unit must display two masthead lights in a vertical line, sidelights, a sternlight, and a special flashing light in accordance with the COLREGs Rule 24, and a diamond shape during the day if the tow length exceeds 200 meters as per Rule 25.
Step-by-step explanation:
The lights and shapes for a vessel being pushed ahead, but not forming a composite unit, are specified in the International Regulations for Preventing Collisions at Sea (COLREGs). According to Rule 24 of the COLREGs, a power-driven vessel when pushing ahead or towing alongside, except in the case of a composite unit, must exhibit:
- two masthead lights in a vertical line,
- sidelights,
- a sternlight,
- and a special flashing light.
In addition, Rule 25 requires that these vessels exhibit shapes during the day, including a diamond shape where it can best be seen to indicate that it is towing and the length of the tow exceeds 200 meters.