Navigation & Seamanship
Terms from Abeam to Waypoint, each linked to related terms and to the desks that work with them.
Entries updated May 2026
Related desks
Terms in Navigation & Seamanship
32 termsAbeam
A direction at right angles (90 degrees) to the fore-and-aft centerline of a vessel.
Astern
Behind the vessel, or moving in a backward direction.
Beam
The width of a vessel at its widest point, measured at the midship section.
Bearing
The horizontal direction of one point from another, measured clockwise from true north, magnetic north, or the heading of a vessel.
Bow
The forward-most part of a vessel's hull, designed to reduce the resistance of the hull cutting through water.
Chart Datum
The reference level from which depths on a nautical chart are measured, typically the lowest astronomical tide (LAT).
Compass Rose
A graduated circle printed on nautical charts showing both true and magnetic north, used to determine bearings and courses.
Course
The intended horizontal direction of travel measured as an angle from north.
Course Over Ground
The actual direction of a vessel's movement over the earth's surface, as determined by GPS or other positioning systems.
Dead Reckoning
A method of estimating a vessel's current position by advancing a known position using the course steered, speed through the water, and time elapsed.
Draft
The vertical distance between the waterline and the lowest point of a vessel's hull, indicating how deep the ship sits in the water.
Draught
The British English spelling of draft, referring to the depth of water a vessel draws.
ECDIS
Electronic Chart Display and Information System, a computer-based navigation system that complies with IMO regulations and can be used as an alternative to paper nautical charts.
Great Circle
The shortest distance between two points on the surface of a sphere, formed by the intersection of the sphere with a plane passing through its center.
Heading
The direction in which a vessel's bow is pointed at any given moment, measured in degrees from north.
Knot
A unit of speed equal to one nautical mile per hour, approximately 1.852 kilometres per hour or 1.151 miles per hour.
Latitude
The angular distance of a point north or south of the equator, measured in degrees, minutes, and seconds from 0 degrees at the equator to 90 degrees at the poles.
Lee Shore
A shore that lies downwind of a vessel, toward which the wind is blowing.
Leeway
The sideways drift of a vessel from its intended course, caused by wind pushing against the hull and superstructure.
Longitude
The angular distance of a point east or west of the Prime Meridian at Greenwich, measured in degrees from 0 to 180.
Magnetic North
The direction indicated by a magnetic compass needle toward the earth's magnetic north pole, which differs from true north by an angle called magnetic variation or declination.
Meridian
A great circle on the earth's surface passing through both the North and South Poles.
Nautical Mile
A unit of distance used in maritime and air navigation equal to approximately 1,852 metres or 1.151 statute miles.
Parallel
A circle on the earth's surface formed by the intersection of a plane parallel to the equator.
Port (Direction)
The left-hand side of a vessel when facing forward (toward the bow).
Rhumb Line
A line on the earth's surface that crosses all meridians at the same angle, appearing as a straight line on a Mercator projection chart.
Speed Over Ground
The speed of a vessel relative to the earth's surface, as measured by GPS or other positioning systems.
Starboard
The right-hand side of a vessel when facing forward (toward the bow).
Stern
The rear-most part of a vessel's hull where the rudder and propeller are typically located.
Transit
The passage of a vessel through a canal, strait, or narrow waterway.
True North
The direction along the earth's surface toward the geographic North Pole, as opposed to magnetic north.
Waypoint
A predetermined geographical position defined by latitude and longitude coordinates, used as a reference point for navigation and route planning.