A vessel servicing a pipeline during the day shall display

• A. One black ball
• B. Two white balls
• C. Three black shapes in a vertical line; the highest and lowest are balls, and the middle one is a diamond
• D. Four black shapes

Answer: (C)

Day shapes tell other mariners what a vessel is doing, so actions don’t surprise nearby traffic. For a vessel servicing a pipeline, the standard daytime signal is three shapes in a vertical line: a ball at the top, a diamond in the middle, and a ball at the bottom. All shapes are black on a white background. This specific pattern clearly communicates underwater or pipeline work, prompting others to give a wider berth and proceed with caution. Other options don’t fit the recognized daytime signal for this operation—the color, number, or arrangement of shapes isn’t correct for pipeline/underwater work.