Which vessel may combine her sidelights and sternlight in one lantern on the centerline?

The correct choice indicates that a 16-meter sailing vessel may combine her sidelights and sternlight in one lantern on the centerline. This provision is based on the International Regulations for Preventing Collisions at Sea (COLREGs), which dictate the navigation lights required for different types of vessels based on their size and nature of operation.

In the case of vessels under 20 meters in length, especially sailing vessels, there is flexibility in the lighting configurations. Specifically, when the vessel is shorter than 20 meters, the rules allow for the arrangement of lights to be simpler, making it permissible for these vessels to combine the sidelights into a single lantern situated on the centerline.

This simplification is practical for smaller vessels, enhancing visibility while complying with safety regulations. Therefore, the ability to combine sidelights and a sternlight in one lantern is appropriate for a sailing vessel of this specified size. Larger vessels and motorized vessels often need to follow more stringent lighting requirements due to their size and complexity of operations.