What should a vessel at anchor display between sunrise and sunset?

A vessel at anchor is required to display one black ball between sunrise and sunset as a visual signal to other vessels. This signal indicates that the vessel is not underway and provides important information for navigational safety. The single black ball has been established as a standard marker to help prevent collisions, especially in busy waterways where other boats may not readily see the anchored vessel.

The reason why this requirement is significant is that it aids in maintaining awareness among all vessels in the area, allowing them to make safe navigational decisions. The other options, which include two black balls or a red ball, are incorrect because they do not conform to the established regulations regarding the appropriate signal for a vessel at anchor. The same applies to the option of displaying two orange and white balls, as this does not pertain to a vessel at anchor and is not a recognized signaling method under maritime rules. Therefore, the display of one black ball serves as a clear and effective signal for a vessel that is at anchor, ensuring safety on the water.