Which vessel is required to display a day shape for a vessel constrained by her draft?

A vessel that is constrained by her draft is one that cannot safely navigate in shallow waters due to her draft limitations. To alert other vessels about her condition, the International Regulations for Preventing Collisions at Sea (COLREGs) stipulate specific day shapes that must be displayed.

For a vessel restricted in her ability to maneuver, such as one that is constrained by her draft, the appropriate day shape is a cylinder. This visual signal serves to inform other mariners of her special operating situation, indicating that the vessel might not be able to maneuver freely, especially around shallow areas.

The other options listed do not pertain to the specific requirement for a vessel constrained by her draft. For instance, a vessel under sail typically displays a different set of day shapes. A vessel at anchor shows a specific day shape that indicates it is stationary and not underway, while a vessel towing another would display a day shape that signifies its towing activity, which differs from the constraints imposed by draft.