BOTH INTERNATIONAL & INLAND You are approaching a vessel dredging during the day and see two balls in a vertical line on the port side of the dredge. These shapes mean that __________.

Correct Answer: Option D — there is an obstruction on the port side of the dredge

COLREGS Rule 27(d) mandates that a vessel engaged in dredging or underwater operations display two balls in a vertical line on the side where an obstruction exists, indicating to approaching mariners the unsafe side to pass.