Piloting & Terrestrial Navigation

Buoys, beacons and lighthouses mark channels and dangers. IALA harmonised them into two regions whose lateral colours are reversed.

The magnetic compass reads a direction corrupted by the Earth's field and the ship's own magnetism. Correcting between true and compass is the most-used skill in practical navigation.

DR advances the last known position by course steered and speed through the water. Adding current and wind converts the DR into an estimated position and the ground track.

Piloting is navigation with the shore in sight, where errors are measured in tens of metres and the response time is short. It is built on lines of position.

Tide is the vertical rise and fall of the water; tidal current is its horizontal flow. They are related but not simultaneous, and both are predicted, not guaranteed.