BOTH INTERNATIONAL & INLAND Which shape must be shown by a vessel 25 meters in length aground during daylight hours?

Correct Answer: Option C — Three black balls

Rule 30(d) of the COLREGS and Inland Rules mandates that a vessel aground shall exhibit three black balls in a vertical line where they can best be seen. This day shape provides clear visual notification to other mariners that the vessel is not under command due to grounding.