Navigation

An advance notice of a navigational change or development for which complete details are not yet available. It allows mariners to anticipate work, new routes, altered aids or hazards before a permanent chart correction can be issued. The notice remains relevant until cancelled, replaced or incorporated into updated products.

A georeferenced digital image of a paper nautical chart. An RNC preserves the chart’s printed appearance but does not contain the same object-based data as a vector ENC. Display scale, edition, corrections and datum remain important, and zooming cannot add source detail.

A navigational publication providing practical coastal and harbour information to supplement charts. It may describe approaches, anchorages, hazards, facilities, local weather, regulations and tidal effects. Pilot books must be kept current with corrections and checked against official charts, notices and local directions.

An official notice of a newly reported or temporary hazard significant to safe navigation. Warnings may concern failed aids, wrecks, military exercises, drifting objects or changes not yet included in charts. They are distributed through coastal, NAVAREA, NAVTEX, satellite and other services and should be incorporated into passage planning and monitoring.

A vessel’s condition when it is under way but has no movement through the water. It remains under way if it is not anchored, made fast to shore or aground. The distinction matters for navigation lights and collision assessment and differs from making no progress over the ground because current may still carry the vessel.

A conformal cylindrical map projection on which rhumb lines appear straight. Angles and local shapes are preserved, making it convenient for marine chartwork, but scale increases toward the poles and areas become greatly exaggerated. Distance must be measured on the nearby latitude scale.

The graduated latitude markings along the sides of a nautical chart. On a Mercator chart, one minute of latitude represents one nautical mile locally, so distance is measured on the latitude scale beside the area concerned. Longitude scale should not normally be used for distance measurement.

A charted or observed line formed by two aligned marks that indicates a safe or defined track. When the rear mark appears vertically above the front mark, the vessel is on the line. Opening the marks shows which side of the line the vessel lies on, making leading lines valuable for pilotage and clearing hazards.

The angle between a vessel’s heading and its direction of movement through the water caused by sideways drift. Wind acting on the hull and rig is the usual cause for sailing vessels. An allowance is applied to heading or course calculations with the correct direction, while current is treated separately as movement of the water…