A vessel is towing two vessels on her starboard side. How should these vessels be lit?

The correct choice is that the two vessels being towed should exhibit two towing lights and two all-round lights.

When a vessel is engaged in towing multiple vessels, the regulations specify that each towed vessel must display appropriate navigation lights to ensure they are properly identified during nighttime or reduced visibility. Each of the towed vessels must show a towing light above the stern light, which signifies that they are being towed. The all-round lights are required to indicate the presence of vessels that are not underway on their own.

This arrangement clearly communicates to other vessels that these are towed vessels and provides safety to avoid potential collisions, especially when they are side by side. The lights help in determining the relative position and movement of the vessels, which is crucial for safe navigation on waterways where multiple vessels operate together.

In different configurations or numbers of towed vessels, such as if there were just one vessel or a specific towing situation, the lighting would differ according to the COLREGs, but for the scenario of two vessels being towed, displaying two towing lights and two all-round white lights is the proper and lawful method to ensure visibility and identification.