What size is the shape used to indicate a cone on a vessel?

The correct answer is that the shape used to indicate a cone on a vessel must be at least 0.5 meters in size. According to the International Regulations for Preventing Collisions at Sea (COLREGs), the specifications for shapes, including the cone used to signify a vessel that is restricted in its ability to maneuver, require a minimum height for visibility and identification purposes.

This dimension ensures that the signal is effectively recognized by other vessels in various conditions, meeting the safety requirements for navigation. The size of the shape is critical for clear communication between vessels, which helps prevent maritime accidents. Understanding these specifications is essential for anyone involved in maritime operations and navigation.

The other options reflect different sizes that do not meet the COLREGS requirements for visibility and effectiveness in signaling. Hence, they do not fulfill the criteria necessary for the cone shape used on a vessel.