What light configuration should a vessel at anchor display?

When a vessel is at anchor, it is required to display one all-round white light that is visible from all directions. This light serves to indicate the vessel's presence to other mariners, especially in situations where visibility may be reduced or at night. The all-round white light must be positioned as high as practicable to enhance its visibility to passing boats.

The other options describe light configurations appropriate for different scenarios. For instance, red and green sidelights are used by vessels that are under way to indicate their intentions and orientation. The use of two all-round white lights is typically designated for specific situations, such as vessels that are constrained by their draft or in special circumstances. Finally, while some small vessels may not require lights under certain regulations, this does not apply to all vessels, especially those that must adhere to more stringent lighting requirements. Thus, displaying one all-round white light is the standard and required configuration for vessels at anchor, ensuring safety and visibility in navigable waters.