Glossary
Marine navigation has its own secret language, and let’s face it—half of it sounds like someone making things up after too much grog. You’ve got your 'dead reckoning,' which isn’t nearly as ominous as it sounds, and 'bearing,' which has nothing to do with polar bears but everything to do with pointing the right way. Don’t even get us started on 'knots'—why measure speed like you’re tying a shoelace? And then there’s 'fix (not for your engine) and 'DR' (spoiler: it’s not a doctor). If you’re baffled, don’t worry—we’re here to help you decipher this nautical code so you can sound like a pro, not a landlubber who’s lost their compass.
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TermDefinition
- General Nautical Terminology, Navigation APEM More Details
- General Nautical Terminology, Navigation Appraise, Plan, Execute, Monitor (APEM) More Details
- General Nautical Terminology, Navigation Bearing
The direction or angle between a reference point, typically true north, and an object or destination, usually expressed in degrees.
A bearing...
More Details - General Nautical Terminology, Navigation Bearing to Waypoint (BTW)
The direction from a vessel's current position to a predetermined navigational point or waypoint.
In marine navigation, Bearing to Waypoint is...
More Details - General Nautical Terminology, Navigation BTW
The direction from a vessel's current position to a predetermined navigational point or waypoint.
In marine navigation, Bearing to Waypoint is...
More Details - Navigation CADET
The CADET mnemonic can help remember the corrections needed when converting between True North and Compass North bearings. It assists in...
More Details - General Nautical Terminology, Navigation, Safety CBDR
A navigational situation where two vessels maintain the same relative bearing to each other while the distance between them diminishes, often...
More Details - General Nautical Terminology, Navigation Chart
A detailed map used in marine navigation, showing water depths, hazards, and other critical information for safe passage.

A marine chart...
More Details - General Nautical Terminology, Navigation Chronometer
A highly accurate timekeeping instrument, specifically designed for determining longitude at sea.
A chronometer is a precision timepiece used...
More Details - General Nautical Terminology, Navigation Closest Point of Approach (CPA)
Used primarily in maritime and aviation contexts to describe the shortest distance that will be achieved between two moving objects, such as...
More Details - General Nautical Terminology, Navigation Cocked Hat
The small triangular area formed when three position lines on a nautical chart intersect but do not meet at a single point, indicating a degree...
More Details - General Nautical Terminology, Navigation COG
The actual path a vessel follows over the surface of the Earth, as opposed to its heading or intended course.
Course Over Ground (COG) is a...
More Details - Navigation Compass Add East for True (CADET)
The CADET mnemonic can help remember the corrections needed when converting between True North and Compass North bearings. It assists in...
More Details - General Nautical Terminology, Navigation Compass Rose
A circular diagram on nautical charts and compasses that displays directions relative to true north and magnetic north, often including...
More Details - General Nautical Terminology, Navigation, Safety Constant Bearing, Decreasing Range (CBDR)
A navigational situation where two vessels maintain the same relative bearing to each other while the distance between them diminishes, often...
More Details - General Nautical Terminology, Navigation Coordinated Universal Time (UTC)
The primary time standard by which the world regulates clocks and time serving as the basis for civil time globally.
Coordinated Universal...
More Details - General Nautical Terminology, Navigation, Weather (Meteorology) Coriolis Effect
The apparent deflection of moving fluids, such as air or water, caused by the Earth's rotation, influencing large-scale ocean currents and wind...
More Details - General Nautical Terminology, Navigation Course Over Ground (COG)
The actual path a vessel follows over the surface of the Earth, as opposed to its heading or intended course.
Course Over Ground (COG) is a...
More Details - General Nautical Terminology, Navigation CPA
Used primarily in maritime and aviation contexts to describe the shortest distance that will be achieved between two moving objects, such as...
More Details - General Nautical Terminology, Navigation Cross Track Error (XTE)
The lateral distance and drift between a vessel's actual position and the intended navigational track or course.
Cross Track Error (XTE) is a...
More Details - General Nautical Terminology, Navigation Current
The continuous, directed movement of seawater or other bodies of water caused by various factors such as wind, tides, and differences in water...
More Details - General Nautical Terminology, Navigation Dead Reckoning (DR)
A navigational method used to estimate a vessel's current position based on a previously known position, factoring in speed, time, and course...
More Details - General Nautical Terminology, Navigation Deviation
The difference between a vessel's actual compass heading and the magnetic heading indicated by the compass.
Deviation is caused by the...
More Details - General Nautical Terminology, Navigation Deviation card
A reference chart used on a vessel to indicate the compass error caused by local magnetic influences, showing the necessary corrections for...
More Details - General Nautical Terminology, Navigation Dilution of Precision (DOP)
Used in satellite navigation and geolocation to provide the likely accuracy of a satellite-derived position.
The DOP concept is essential to...
More Details - General Nautical Terminology, Navigation Direction of Buoyage
The direction in which lateral marks (port and starboard buoys) should be passed when entering a harbour or following a main channel, based on...
More Details - General Nautical Terminology, Navigation Distance to Waypoint (DTW)
The measured distance, typically in nautical miles, between a vessel's current position and a predetermined navigational point or...
More Details - General Nautical Terminology, Navigation Dividers
A navigational tool consisting of two hinged legs with pointed ends, used by mariners to measure distances on a nautical chart.

Dividers...
More Details - General Nautical Terminology, Navigation DOP
Used in satellite navigation and geolocation to provide the likely accuracy of a satellite-derived position.
The DOP concept is essential to...
More Details - General Nautical Terminology, Navigation DR
A navigational method used to estimate a vessel's current position based on a previously known position, factoring in speed, time, and course...
More Details - General Nautical Terminology, Navigation DTW
The measured distance, typically in nautical miles, between a vessel's current position and a predetermined navigational point or...
More Details - General Nautical Terminology, Navigation Ebb Tide
The period during which the tide is receding, causing water levels to fall as it flows away from the shore towards the sea.
Ebb tide is a...
More Details - General Nautical Terminology, Navigation ECDIS
An Electronic Chart Display and Information System (ECDIS) is a geographic information system used for nautical navigation that complies with IMO...
More Details - General Nautical Terminology, Navigation Electronic Chart Display and Information System (ECDIS)
An Electronic Chart Display and Information System (ECDIS) is a geographic information system used for nautical navigation that complies with IMO...
More Details - General Nautical Terminology, Navigation Electronic Navigation Chart (ENC)
A digital database of maritime chart information designed for use with Electronic Chart Display and Information Systems (ECDIS) to support safe...
More Details - General Nautical Terminology, Navigation ENC
A digital database of maritime chart information designed for use with Electronic Chart Display and Information Systems (ECDIS) to support safe...
More Details - General Nautical Terminology, Navigation EP
The approximate location of a vessel determined by dead reckoning, and accounting for external factors such as wind (Leeway) and Tide.
An...
More Details - General Nautical Terminology, Navigation Estimated Position (EP)
The approximate location of a vessel determined by dead reckoning, and accounting for external factors such as wind (Leeway) and Tide.
An...
More Details - General Nautical Terminology, Navigation Estimated Time of Arrival (ETA)
The predicted time at which a vessel is expected to reach a specific destination, based on current speed, course, and environmental...
More Details - General Nautical Terminology, Navigation ETA
The predicted time at which a vessel is expected to reach a specific destination, based on current speed, course, and environmental...
More Details - General Nautical Terminology, Navigation Flood Tide
The incoming or rising phase of the tide, during which seawater flows landward and the water level increases.
A flood tide is the period...
More Details - General Nautical Terminology, Navigation Global Navigation Satellite System (GNSS)
The collective set of systems that enables positioning devices to calculate latitude & longitude. The system includes solutions including the GPS...
More Details - General Nautical Terminology, Navigation GMT
The mean solar time at the Prime Meridian in Greenwich, London, used as a global time standard.
Greenwich Mean Time (GMT) is a timekeeping...
More Details - General Nautical Terminology, Navigation Gnomonic Projection
A type of map projection where the surface of the Earth is projected onto a plane from the centre of the globe, causing great circles to appear...
More Details - General Nautical Terminology, Navigation GNSS
The collective set of systems that enables positioning devices to calculate latitude & longitude. The system includes solutions including the GPS...
More Details - General Nautical Terminology, Navigation Greenwich Mean Time (GMT)
The mean solar time at the Prime Meridian in Greenwich, London, used as a global time standard.
Greenwich Mean Time (GMT) is a timekeeping...
More Details - General Nautical Terminology, Navigation HAT
The highest level of sea water that can be predicted to occur under average meteorological conditions and under any combination of astronomical...
More Details - General Nautical Terminology, Navigation HDOP
Used in satellite navigation and positioning systems to quantify the accuracy of horizontal position measurements. It is a unitless factor that...
More Details - General Nautical Terminology, Navigation Heading
The direction in which a vessel's bow is pointed at any given moment, typically measured in degrees relative to true north or magnetic...
More Details - General Nautical Terminology, Navigation Height of Light
The vertical distance from the water's surface at Mean High Water Springs to the focal plane of a lighthouse's light source.
Height of Light...
More Details - General Nautical Terminology, Navigation Height of Tide
The vertical distance between the water's surface at any given time and the established chart datum, typically the lowest astronomical...
More Details - General Nautical Terminology, Navigation Highest Astronomical Tide (HAT)
The highest level of sea water that can be predicted to occur under average meteorological conditions and under any combination of astronomical...
More Details - General Nautical Terminology, Navigation Horizontal Dilution of Precision (HDOP)
Used in satellite navigation and positioning systems to quantify the accuracy of horizontal position measurements. It is a unitless factor that...
More Details - Did you know?, General Nautical Terminology, Navigation IDL
An imaginary longitudinal line located at approximately 180 degrees longitude serving as the demarcation where the calendar date changes by one...
More Details - General Nautical Terminology, Navigation IHO
An intergovernmental organisation dedicated to ensuring the uniformity and standardisation of hydrographic and nautical charting practices...
More Details - Did you know?, General Nautical Terminology, Navigation International Date Line (IDL)
An imaginary longitudinal line located at approximately 180 degrees longitude serving as the demarcation where the calendar date changes by one...
More Details - General Nautical Terminology, Navigation International Hydrographic Organization (IHO)
An intergovernmental organisation dedicated to ensuring the uniformity and standardisation of hydrographic and nautical charting practices...
More Details - Did you know?, Navigation International Meridian Conference
A diplomatic meeting held in 1884 in Washington, D.C., where representatives from 25 nations convened to establish a standard prime meridian for...
More Details - General Nautical Terminology, Navigation Knot
A unit of speed used in maritime navigation, equivalent to one nautical mile per hour.
A knot is a crucial measurement in marine navigation,...
More Details - General Nautical Terminology, Navigation LAT
The lowest level that sea tides can reach under normal meteorological conditions, based on astronomical influences such as the gravitational pull...
More Details - General Nautical Terminology, Navigation Latitude
The angular distance of a location on Earth's surface, measured in degrees(°), minutes('), and seconds('') north or south of the equator which is...
More Details - General Nautical Terminology, Navigation Lines of Position (LOP)
Navigational lines drawn on a chart, each representing a possible location of a vessel based on a single observation or measurement.
A line...
More Details - General Nautical Terminology, Navigation Longitude
The geographic coordinate that specifies the east-west position of a point on the Earth's surface, measured in degrees(°), minutes(') and...
More Details - General Nautical Terminology, Navigation LOP
Navigational lines drawn on a chart, each representing a possible location of a vessel based on a single observation or measurement.
A line...
More Details - General Nautical Terminology, Navigation Lowest Astronomical Tide (LAT)
The lowest level that sea tides can reach under normal meteorological conditions, based on astronomical influences such as the gravitational pull...
More Details - General Nautical Terminology, Navigation Maritime Safety Information
Defined in the Safety of Life at Sea (SOLAS) Convention, Chapter IV as "navigational and meteorological warnings, meteorological forecasts and...
More Details - General Nautical Terminology, Navigation Mean High Water Springs (MHWS)
A tidal datum representing the average height of the high water level during spring tides over a specific period, typically measured over a...
More Details - General Nautical Terminology, Navigation MHWS
A tidal datum representing the average height of the high water level during spring tides over a specific period, typically measured over a...
More Details - General Nautical Terminology, Navigation Nautical Mile
A nautical mile is a unit of measurement used in maritime navigation that is equivalent to one minute of latitude or approximately 1.852...
More Details - General Nautical Terminology, Navigation Navigational Telex (NAVTEX)
A maritime communication system used for the automatic broadcast of navigational and meteorological warnings, forecasts, and urgent safety...
More Details - General Nautical Terminology, Navigation NAVTEX
A maritime communication system used for the automatic broadcast of navigational and meteorological warnings, forecasts, and urgent safety...
More Details - General Nautical Terminology, Navigation Neap Tide
When the difference between high and low water is at its smallest, typically occurring twice a month during the first and third quarters of the...
More Details - General Nautical Terminology, Navigation NM
A Notice to Mariners is an official publication issued by maritime authorities to provide important information and updates regarding...
More Details - General Nautical Terminology, Navigation Notice to Mariners (NM)
A Notice to Mariners is an official publication issued by maritime authorities to provide important information and updates regarding...
More Details - General Nautical Terminology, Navigation, Safety Passage
A journey or route taken by a vessel from one location to another, often across open water or between specific points such as harbours or...
More Details - General Nautical Terminology, Navigation, Safety Passage Plan
A detailed, structured navigational strategy outlining the safest and most efficient route for a vessel from departure to destination,...
More Details - General Nautical Terminology, Navigation PDOP
Measurement of the geometric strength of satellite configuration in a Global Navigation Satellite System (GNSS) receiver.
It quantifies the...
More Details - General Nautical Terminology, Navigation Pilotage
Pilotage is the use of fixed visual references by sight or radar to safely navigate to a destination, usually a port or harbour, with the help of...
More Details - General Nautical Terminology, Navigation Portland Plotter
A navigational tool used in marine chartwork to measure and plot courses, bearings, and distances on nautical charts.

The Portland Plotter...
More Details - General Nautical Terminology, Navigation Position Dilution of Precision (PDOP)
Measurement of the geometric strength of satellite configuration in a Global Navigation Satellite System (GNSS) receiver.
It quantifies the...
More Details - General Nautical Terminology, Navigation Prime Meridian
The zero-degree longitude line that is the starting point for measuring longitude and dividing the Earth into the Eastern and Western...
More Details - General Nautical Terminology, Navigation Range of Tide
The vertical difference between the high tide and the succeeding low tide in a specific tidal cycle.
The range of tide is a fundamental...
More Details - General Nautical Terminology, Navigation Rate (Tidal Stream)
The speed at which a tidal stream flows, typically measured in knots.
The rate of a tidal stream is the velocity at which the water moves due...
More Details - General Nautical Terminology, Navigation RYA Handy Plotter
A lightweight Plotter, suitable for use in a classroom for navigation exercises.

This handy size plotter has been specifically designed to...
More Details - Navigation RYA Training Almanac
Publication compiled to support RYA Theory courses. The RYA Training Almanac contains exerts that mimic Nautical Almanacs in the real world.

- Navigation RYA Training Chart
A specialised, non-navigational chart produced by the Royal Yachting Association (RYA) for teaching and practising navigation and chartwork...
More Details - General Nautical Terminology, Navigation S-100 Universal Hydrographic Data Model
An international standard developed by the International Hydrographic Organization (IHO) for the management, exchange, and interoperability of...
More Details - General Nautical Terminology, Navigation Sailing Directions
Sailing directions, also known as nautical directions or pilots, are publications that provide detailed information for navigating coastal and...
More Details - General Nautical Terminology, Navigation Secondary Port
A location where tidal information is derived by applying corrections to data from a nearby Standard Port.
A secondary port is a coastal...
More Details - General Nautical Terminology, Navigation Set
The direction which a current flows in a body of water.
In marine navigation, understanding the set of a current is crucial for plotting an...
More Details - General Nautical Terminology, Navigation Set
The process of securing a boat in a stationary position by deploying and embedding an anchor into the seabed.
When a mariner 'sets anchor',...
More Details - General Nautical Terminology, Navigation Slack Water
The short period of still water occurring at the turn of the tide, when the tidal current changes direction and its speed is minimal.
Slack...
More Details - General Nautical Terminology, Navigation Small Vessel Electronic Chart Systems (SV-ECS)
Electronic navigation standards for commercial vessels less than 24m .
Equipment meeting the requirements of this performance standard is...
More Details - General Nautical Terminology, Navigation SOG
The actual velocity of a vessel relative to the Earth's surface, accounting for the effects of currents, tides, and other environmental...
More Details - General Nautical Terminology, Navigation Speed Over Ground (SOG)
The actual velocity of a vessel relative to the Earth's surface, accounting for the effects of currents, tides, and other environmental...
More Details - General Nautical Terminology, Navigation Speed Through Water (STW)
The velocity at which a vessel moves relative to the water it is travelling through, excluding the effects of current or tidal flow.
Speed...
More Details - General Nautical Terminology, Navigation Spring Tide
A tide with the greatest difference between high and low water occurring when the Sun, Moon, and Earth are aligned during new and full...
More Details - General Nautical Terminology, Navigation Standard Port
A primary tidal reference location for which full tidal predictions, including times and heights of high and low water, are...
More Details - General Nautical Terminology, Navigation STW
The velocity at which a vessel moves relative to the water it is travelling through, excluding the effects of current or tidal flow.
Speed...
More Details - General Nautical Terminology, Navigation Superbuoy
Large buoys, generally more than 5 m in diameter, are distinguished on charts because their unusually large size renders them a potential hazard...
More Details

