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Separate the direction the boat points from its movement across the chart. Navigation quantities need a reference, a unit and a source before they can be meaningfully compared.
Navigation brands & tutorials →MarineBrands editorial definitions · Reviewed 5 October 2026 · Examples explain context, not operating procedures.
12 of 12 terms
Also find under: BRG
The direction from one position towards another, expressed against a stated reference.
Check whether a bearing is true, magnetic or relative before comparing numbers.
Also find under: CD
The reference level from which charted depths and related tidal heights are measured.
Confirm that tide information and the chart use compatible references before comparing them.
Also find under: COG
The direction of the vessel’s movement over the Earth’s surface.
A GNSS-derived course describes motion, so it should not be assumed to equal bow direction.
Also find under: HDG
The direction in which the vessel’s bow points, expressed against a stated north reference.
Heading can differ from the path over the seabed when current or leeway acts.
Also find under: lat
Angular position north or south of the equator.
Keep the hemisphere and coordinate format when passing a position to someone else.
Also find under: lon long
Angular position east or west of the reference meridian.
Minutes and decimal degrees are different formats; copy the complete position convention.
Also find under: NM nmi
A unit of distance equal to 1,852 metres.
Keep nautical miles separate from land miles when reading ranges or planning distances.
An ordered series of navigation legs or waypoints.
An automatically proposed route still requires appropriate checking against current information and the vessel.
Also find under: SOG
The rate of movement relative to the Earth’s surface.
Current can make this differ from speed through the water without either sensor being wrong.
Also find under: STW boat speed
The vessel’s speed relative to the surrounding water.
Compare the sensor type and calibration before using it alongside ground speed.
Also find under: UKC
The vertical separation between the lowest relevant part of a vessel and the seabed.
A simple chart-depth subtraction omits factors such as tide, motion and uncertainty.
A stored geographical position used as a reference in navigation.
A saved waypoint records a position; it does not establish that reaching it is safe or permitted.
Original concise explanations for equipment research. Use these specialist resources for the wider technical context and the relevant current documentation for a particular product or activity.
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