Which light signals a vessel that is both anchored and greater than 50 meters?

The correct answer is that a vessel that is both anchored and greater than 50 meters in length must display a second all-around light. According to the COLREGs, vessels at anchor are required to show a specific configuration of lights to indicate their status to others.

For vessels over 50 meters in length, this is accomplished by having a second all-around white light positioned higher than the first one, significantly enhancing visibility and ensuring that other vessels can easily recognize that the ship is anchored. This requirement helps prevent collisions and improves safety in navigational waters.

The other options do not adhere to the requirements set forth in the COLREGs for anchored vessels of this size. For example, a blue light on the bow, while it may signify certain conditions in specific contexts, does not fulfill the legal lighting requirements for an anchored vessel. Similarly, having only the initial all-around light fails to provide adequate identification for larger vessels at anchor. Flashing red and white lights are typically associated with different navigational statuses and not with the display of lights required for an anchored vessel. Thus, having a second all-around light is the appropriate measure to follow, ensuring compliance with international regulations for safe navigation.