What is the purpose of Cardinal marks on nautical charts?

• A. Shows depth contour
• B. Marks the location of a reef
• C. Indicates safe water direction
• D. Marks the location of a channel

Answer: (C)

Cardinal marks are used to show where the safe water lies relative to a hazard. They indicate the direction you should pass in order to stay in safe water around that hazard. There are four kinds, each corresponding to a direction (north, east, south, or west), and the mark tells you which side of it is the safe side. For example, a mark indicating safe water to the north means you should stay north of that mark as you pass.

This is the best answer because cardinal marks are specifically about guiding vessels by the direction of safe water, rather than showing depth (depth contours), marking a reef, or pinpointing a channel. Those functions are handled by other types of marks or chart features.