Which visual signal indicates that a vessel is constrained by its draft?

The visual signal that indicates a vessel is constrained by its draft is represented by three all-round red lights. This specific configuration is used to communicate to other vessels that the ship has significant draft constraints, meaning it cannot maneuver as freely as other types of vessels might in certain waters. The three all-round red lights are aligned vertically, making them easily recognizable for their intended signaling.

This signal plays a crucial role in maritime navigation, especially in constrained waters, ensuring that other vessels are aware of the limitations the constrained vessel faces due to its draft. Understanding these signaling conventions is critical for mariners to prevent collisions and ensure safe navigation in proximity to such vessels.

While other options consist of different combinations of lights, they signify other limitations or statuses that do not pertain specifically to the draft constraint of a vessel. Hence, the three all-round red lights distinctly identify a vessel's constrained status regarding its draft.