Which day shape indicates a vessel aground?

• A. One black ball
• B. Two black balls in a line
• C. Three black balls in a line
• D. A black diamond

Answer: (C)

Day shapes show a vessel’s status in daylight to help others avoid collisions. When a vessel is aground, it cannot effectively maneuver, so the signal used is three black balls arranged in a vertical line. This combination clearly communicates restricted ability to maneuver due to grounding, signaling others to give wide space and proceed with caution. The other shapes don’t indicate grounding: a single black ball means a vessel at anchor, two black balls in a vertical line indicate a vessel not under command, and a black diamond isn’t the standard day shape for an aground vessel.