Which vessel may combine her sidelights in one lantern on the fore and aft centerline of the vessel?

The vessel that may combine her sidelights in one lantern on the fore and aft centerline is a sailing vessel that is 20 meters or less in length. This regulation allows for a simplified lighting arrangement, which aids in reducing the equipment necessary for smaller vessels.

For a 16-meter sailing vessel, combining the sidelights into a single lantern is permissible, thus ensuring efficient visibility while adhering to navigation rules. This arrangement is beneficial for vessels that may not have the space or resources to accommodate multiple individual lights.

Larger vessels, such as power-driven or sailing vessels over the specified length, must follow different lighting configurations that require distinct sidelights. These configurations are essential for larger vessels to ensure visibility and safety on the water, especially in the presence of other vessels and in varying maritime conditions. Non-self-propelled vessels also have specific regulations regarding their lighting systems, which may not allow for the combination of sidelights.