What is the primary purpose of an anchor light on a boat?

The primary purpose of an anchor light on a boat is to indicate the presence of the vessel at anchor during nighttime. This light is typically mounted at the highest point on the vessel and is designed to be visible from all directions, thereby alerting other vessels that the boat is not underway but is instead stationary. This is crucial for safety, as it helps prevent collisions by making the anchored vessel visible to other boats navigating in the area. The anchor light must meet specific standards regarding brightness and positioning to ensure it effectively serves its purpose.

While other options may seem plausible, they do not accurately reflect the anchor light's intended function. For instance, powering the navigation system does not relate directly to the role of an anchor light. Similarly, although signaling to other vessels to keep their distance is indirectly achieved through the presence of the anchor light, it is not its primary function. Finally, providing illumination for deck activities is also not a purpose of the anchor light; other types of lights, such as deck lights, are used for that reason. Therefore, option B clearly captures the essential role of the anchor light in maritime safety and navigation.