Navigation and Position Determination
What the exam tests
Navigation and Position Determination tests independent position fixing, chart and ECDIS work, compass error, tidal calculations and passage planning under Norwegian and international practice. Answers must show the method, not just a final position.
Core rules and concepts
- Fix by at least three position lines; a cocked hat is an error ellipse, not proof of a true fix.
- Apply gyro error and magnetic variation/deviation before plotting true bearings. Check the sign of gyro error carefully.
- Use a running fix when only one object is available; advance the earlier line by course and distance.
- ECDIS must use official ENC, correct safety settings and a route check; cross-check with radar, visual bearings or soundings.
- GNSS integrity: monitor HDOP/VDOP, RAIM and unexpected jumps; do not treat one GNSS fix as an independent cross-check.
- Tidal height comes from chart datum plus height of tide; UKC must also allow for squat, heel and chart accuracy.
Worked example
A vessel steams 000°T at 10 kn. At 1000 a lighthouse bears 090°T; at 1030 it bears 045°T. Run in 0.5 h = 5 nm. Relative bearings from course are 90° and 45°, change 45°. Distance at 1030 = run × sin 90° × sin 45° / sin 45° = 5 nm. Plot the 045°T bearing from the lighthouse at 5 nm. Confirm with a radar range or sounding.
Traps
Plotting compass bearings as true; forgetting the sign of gyro error; using a single GNSS fix as a cross-check; ignoring set and drift in a running fix; and treating an ECDIS route check as a one-off.
Key points: three position lines; gyro error signs; running fix method; ENC and route check; GNSS integrity monitoring; UKC allowance.