Your vessel has changed course and is heading 285°T, you are on the charted range and it appears as in illustration D048NG below. After several minutes the range appears as in illustration D047NG below and your heading is still 285°T. What does this indicate?

Correct Answer: Option D — north-setting current

According to Bowditch, a range that continues to open while maintaining course indicates an external set, such as a north-setting current acting perpendicular to the intended track, pushing the vessel progressively off the line despite constant heading.