Navigation
From chart to fix
Candidates must understand the Earth's shape and the coordinate system, chart projections and their distortions, the triangle of velocities, track and heading, drift, wind correction angle, and the calculation of groundspeed and ETA. Learn the use of the navigation computer, the plotting of fixes, and the principles of dead reckoning, pilotage and radio navigation. Understand the meaning of true, magnetic and compass headings, and the variation and deviation that connect them.
Traps in questions
A frequent trap is mixing up track and heading, or applying variation in the wrong direction. Another is forgetting that wind affects groundspeed and drift simultaneously. Questions also test the difference between a rhumb line and a great circle, and the effect of projection on the apparent shape of a route.
Worked example
"True track 090°, variation 5°E, deviation 2°W. What is the compass heading?" Answer: magnetic = 090° − 5° = 085°; compass = 085° + 2° = 087°. Rule of thumb: east is least, west is best for applying variation to convert true to magnetic.
Key points
- Understand the triangle of velocities and drift.
- Distinguish track, heading, variation and deviation.
- Apply the east-is-least rule correctly.
- Wind affects groundspeed and drift at the same time.
- Know rhumb line versus great circle.