Navigation General: Piloting, Buoyage, and Compass Work
Piloting fundamentals
Navigation General questions reward precise chart and compass work. Know how to plot a fix from two or more intersecting lines of position, how a running fix works, and how dead reckoning differs: DR uses only course and speed, while an estimated position (EP) adds set and drift. Set is the direction a current flows toward; drift is its speed. Remember that course steered, course made good, and heading differ when leeway or current is present.
Aids to navigation and chart symbols
U.S. waters use IALA Region B. Returning from sea, red buoys are on your starboard side, green on your port: "red right returning." Red buoys carry even numbers and green carry odd. Know preferred-channel marks, safe-water marks, isolated-danger marks, special marks, and cardinal marks, plus light rhythms: Fl (flashing), Iso (equal light and dark), Oc (occulting, light longer than dark), Q (quick), VQ (very quick), and Mo (Morse). Chart soundings are measured from chart datum, normally MLLW, and are not the same as depths at any given moment.
Traps
Questions often test compass conversion, buoy identification, and light rhythm recognition. Use "Can Dead Men Vote Twice, Add East": Compass + Deviation = Magnetic; Magnetic + Variation = True; add easterly error, subtract westerly error. Going from true to compass reverses the signs. Watch whether an error is east or west and whether the question asks for true, magnetic, or compass.
Worked example
Compass course 052°, deviation 3°E, variation 10°W. Compass 052 + 3°E = magnetic 055. Magnetic 055 - 10°W = true 045. Check by reversing: true 045 + 10°W = 055 magnetic; 055 - 3°E = 052 compass.