Navigation

The systematic measurement of depths, seabed features, shoreline and other information needed to describe navigable waters. Modern surveys combine positioning, echo sounding, sonar, tide observations and quality control. Results support nautical charts and publications, but coverage, date and uncertainty must be considered when assessing hazards.

The maritime buoyage region in which port-hand lateral marks are red and starboard-hand lateral marks are green when following the conventional direction of buoyage. Region A covers most of Europe, Africa, Asia and Australasia. Shape, topmark, light and numbering also identify lateral marks, and cardinal and other mark types are common to both IALA regions.

The maritime buoyage region in which port-hand lateral marks are green and starboard-hand lateral marks are red when following the conventional direction of buoyage. Region B includes the Americas, Japan, Korea and the Philippines. Mariners must confirm the region and direction of buoyage rather than relying on colour alone.

The internationally adopted zero-longitude reference used by modern terrestrial coordinate systems. It lies close to, but not exactly on, the historic Greenwich transit-circle meridian because modern datums are geocentric. Navigation systems and charts normally express longitude within a stated geodetic datum tied to this reference.

A route that follows, or approximates, the shortest path between two positions on the Earth’s surface. Its course normally changes continuously and may be planned as a series of waypoints or composite legs to avoid high latitudes, weather, ice or hazards. It is most advantageous over long distances.

The path actually followed by a vessel or craft over the Earth’s surface. It results from heading and through-water or air motion combined with current, leeway or wind. Ground track is distinct from the intended route and is commonly monitored by GNSS and plotted positions.

The shorter distance between two points measured along a great circle on a sphere. It is the minimum spherical route distance and is especially relevant on long ocean passages. On the ellipsoidal Earth, geodesic calculations provide greater precision, while a Mercator chart represents the great-circle track as a curve except in special cases.

The detailed pilotage plan for leaving a berth, harbour or constrained waterway. It covers unberthing, communications, tidal and weather limits, courses, clearing bearings, traffic, abort options and the transition to the main passage. Responsibilities and contingencies should be briefed before lines are let go.