When should shapes be displayed by vessels?

The display of shapes by vessels is crucial for ensuring safe navigation and communication between ships, particularly during the day. Vessels are required to exhibit appropriate shapes from sunrise to sunset regardless of visibility conditions. This requirement helps communicate a vessel's status or activity (such as whether it is at anchor, aground, or restricted in ability to maneuver) to other vessels in the vicinity, contributing to maritime safety.

By displaying shapes during daylight hours, vessels can alert others to their presence and intentions, which is essential even when visibility is good, as other vessels may be relatively close. This regulation ensures that all vessels adhere to a standard method of indicating their status, thereby reducing the risk of collisions and misunderstandings at sea.

In contrast, shapes are not limited to specific times or conditions, as indicated by the other options. Certain situations might require lights at night or during restricted visibility, but shapes are a continuous requirement during daylight hours regardless of those factors. Displaying shapes solely when anchored or only at certain times would compromise the effectiveness of these communication methods in various navigational contexts.