What light should a power-driven vessel display when at anchor?

When a power-driven vessel is at anchor, it is required to display an all-around white light. This light is visible from all directions, which helps ensure that other vessels can easily see the anchored vessel, contributing to safety and navigation in open waters. The reason the all-around white light is specifically mandated is to clearly indicate the vessel's presence to other mariners, especially during low visibility conditions such as nighttime or fog.

The all-around white light allows other vessels to recognize that the power-driven vessel is not underway, which minimizes the risk of collisions that could occur if other vessels mistook the anchored vessel for one that is moving. This is a standard requirement outlined in the International Regulations for Preventing Collisions at Sea (COLREGS) to ensure safe navigation.

Other lighting configurations, such as red sidelights or two vertically aligned masthead lights, are used for vessels that are underway, indicating their course and direction of travel, which is not relevant when the vessel is anchored. A stern light alone would not effectively communicate to approaching vessels the anchored state of the vessel, as it does not provide comprehensive visibility from all angles. Thus, the use of an all-around white light is the appropriate and required indication when a power-driven vessel is at anchor.