Coastal Skipper and Yachtmaster Quiz · Chartwork and passage planning
The course drawn on the chart is 084°T. Using the variation shown and this deviation curve, what course do you steer by the ship's compass?
A deviation curve: a graph of deviation, from 4°W to 4°E with a line for every degree, against the ship's magnetic heading from 000° to 360° with a line every 45 degrees. The curve is a single smooth wave: zero at 000°, rising to a peak of 4°E at 090°, back to zero at 180°, down to 4°W at 270° and back to zero at 360°. A note reads: variation 6°W.
Show the answer
086°C. Go from true to magnetic first: add the 6° westerly variation to get 090°M. Then read the deviation for that heading from the curve, 4°E, and subtract it because it is easterly: 086°C. Deviation changes with the heading, so always enter the curve with the heading you are about to steer.
