Navigation and Chartwork
Navigation and chartwork is a heavy scoring domain in the Greek Category A paper: plotting fixes, courses and estimated positions on Hellenic Navy Hydrographic Service (ΧΥΣ/ΥΝ) charts, converting between compass and true, and solving the drift, current and leeway problems that decide whether a passage plan is safe. Questions are numeric and practical, and they expect you to read the chart extract and the vessel's deviation table correctly.
Charts, datum and symbols
- Depths are in metres below chart datum, roughly the lowest level the sea is expected to reach; drying heights are underlined; heights of lights and landmarks are above mean high water.
- Greek waters are IALA Region A: red can buoys to port, green cone buoys to starboard when entering from seaward. Cardinal marks use black/yellow; isolated danger is black with red bands and two black balls.
- The compass rose gives variation at the edition date plus annual change in minutes - update it to the current year before use.
- Note chart cautions such as "positions approximate" for buoys and unsurveyed areas.
Compass to true (TVMDC)
Compass → Deviation → Magnetic → Variation → True. Add easterly errors, subtract westerly. Read deviation for the compass heading, interpolating between table values. A hand-bearing compass carried away from the boat's own magnetism needs variation only.
Fixing and course to steer
A three-bearing fix is stronger than two; a cocked hat means a small constant error - suspect a compass error rather than a plotting error. Current set is the direction toward which it flows; drift is its speed.
Worked example
Boat speed 6.0 kn through water, required track 090°T, current setting 180°T at 2.0 kn. The current pushes you south, so you must steer north of the track: angle = arcsin(2/6) = 19.5°, so course to steer = 090 − 19.5 = 070.5°T. Speed made good = √(36 − 4) = 5.66 kn, so 12 NM takes 2 h 07 m. Reasoning: the water track must form a triangle with the current vector to give the required ground track.
Traps that cost marks
- Using speed through water for passage time with current or leeway running.
- Applying deviation to a hand-bearing compass bearing.
- Confusing set with drift, or drawing the current in the wrong direction.
- Assuming Mediterranean conditions mean no water-level change: tides are small, but meltemi-driven surges and strong currents in straits (Kafireas, Euripus) matter.
- Plotting fixes on the buoy's charted position rather than its observed one.