What daytime shape is required for a vessel constrained by draft?

A vessel constrained by draft is required to display a shape that represents its restriction of movement. The correct daytime shape is a cylinder. This is used to indicate that the vessel is unable to maneuver easily because of its deep draught. According to the International Regulations for Preventing Collisions at Sea (COLREGs), the cylindrical shape effectively communicates to other vessels that extra caution is needed when navigating in the proximity of the constrained vessel.

In contrast, the other shapes listed have specific meanings: a diamond typically signifies a vessel that is engaged in fishing but not at anchor, a square indicates a vessel at anchor, and a ball is used to indicate a vessel operating with a towing or a vessel that is not under command. Thus, the cylindrical shape is the appropriate signal for a vessel constrained by draft, making it essential for safe navigation in shared waterways.