On a Mercator chart, which line allows navigation by maintaining a constant bearing?

• A. Rhumb line
• B. Great circle
• C. Isobar
• D. Meridian

Answer: (A)

On a Mercator chart, the line that allows navigation by maintaining a constant bearing is the rhumb line. A rhumb line is a path that cuts all meridians at the same angle, meaning you can keep a single compass heading throughout the voyage. Because the Mercator projection preserves angles, this constant bearing translates to a straight line on the chart, making it practical to steer by a fixed bearing from start to destination.

Great-circle routes, while the shortest path on a globe, appear curved on a Mercator chart and would require changing your bearing to stay on course. Isobars have to do with atmospheric pressure, not navigation bearings. Meridian lines are longitudes and indicate north-south direction, but the general navigation concept of a single fixed bearing across a voyage is represented by a rhumb line.