What action signifies "vessel at anchor in distress"?

The correct answer is tied to the requirements outlined in the COLREGs for vessels signaling their status when at anchor and in distress. When a vessel is at anchor and requires assistance, it must display appropriate lights and signals as specified by the rules to alert other vessels to its situation. This includes using the proper distress signals that convey the message of being in need of help while ensuring visibility and recognition by others on the water.

Displaying a red flag is a commonly recognized emergency signal, but it specifically indicates a "vessel in distress" in certain contexts but not for vessels at anchor. Sounding a continuous horn is a sound signal that might attract attention, but it lacks the specificity required by the COLREGs regarding visual distress signals. Hoarding supplies does not communicate any distress to other vessels and does not adhere to the required signaling procedures for conveying a vessel at anchor in distress. Thus, adhering to the protocols outlined in the COLREGs with the correct lighting and signals is essential for ensuring safe navigation and effective response by nearby vessels.