Which of the following is NOT a requirement for vessels anchored in a traffic separation scheme?

Anchored vessels within a traffic separation scheme do have specific requirements to ensure safe navigation and avoid collisions. Among these requirements, sounding a horn regularly is not a mandated practice for vessels at anchor. Instead, vessels must comply with navigation lights and sound signaling obligations as outlined in the International Regulations for Preventing Collisions at Sea (COLREGS) when they are maneuvering or at anchor, but there is no specific requirement for them to sound a horn at regular intervals while anchored in a traffic separation scheme.

In contrast, displaying proper anchor lights is essential for visibility to other vessels, having a crew member on watch ensures someone can respond to any potential dangers or maneuvering requirements, and displaying an anchor shape indicates that the vessel is anchored, which is relevant to avoiding collisions in an area where ship traffic is regulated. Thus, while these three practices are necessary for ensuring safety and compliance, regularly sounding a horn is not a requirement for anchored vessels in such schemes.