Maritime Glossary (A-Z)

Directional reference toward the stern (rear) of a ship.

Directional term meaning toward the stern (rear) of the ship. Astern means backward movement.

The vertical distance from the surface of the water to the highest point on a ship, usually the top of a mast. Crucial for passing safely under bridges or power lines.

The angular distance of a celestial body above the horizon, measured by a sextant.

The middle section of a vessel.

An automated tracking system that displays other vessels in the vicinity. It broadcasts a ship's identity, position, course, and speed to other ships and coastal authorities.

The true bearing or horizontal direction of a celestial body from the observer.

Water pumped into a ship's ballast tanks to improve its stability, balance, and structural integrity when it is not carrying enough heavy cargo.

The study of underwater depth of ocean floors.

Horizontal direction of an object from the observer.

The lowest inner part of a ship's hull.

A vital legal document issued by a carrier to a shipper that details the type, quantity, and destination of the goods being carried. It serves as a receipt of shipment.

The stand housing the ship's compass.

The conventional measure of the pulling (or towing) power of a watercraft, usually a tugboat. Measured in tonnes (TBP).

A transversal propulsion device built into, or mounted to, either the bow or stern of a ship to make it more maneuverable during docking.

The width of a ship at its widest point.

The command center of the ship.

A merchant ship specially designed to transport unpackaged bulk cargo, such as grains, coal, ore, and cement, in its cargo holds.

Unpackaged cargo like grain, coal, or ore.

An upright wall within the hull of a ship. They compartmentalize the ship for structural rigidity and watertight safety.

The intricate process of supplying a ship with fuel (bunker) for its engines. It requires strict adherence to safety and environmental protocols to prevent spills.

Fuel stored and used by the vessel.

A distance equating to one-tenth of a nautical mile.

Ultra-large cargo vessels too large to transit the Suez or Panama Canals. To travel between oceans, they must round the Cape of Good Hope or Cape Horn.

A rotating machine for applying force to mooring ropes.

The practice of position fixing using observation of celestial bodies like the sun, moon, and stars.

A legally binding maritime contract between a shipowner and a charterer for the hire of either a ship for the carriage of passengers or cargo, or of a yacht for pleasure purposes.

An empty space or void lying between two bulkheads or decks within a ship, designed to form a barrier against toxic gas leaks, fire spread, or cargo contamination (e.g. between a fuel tank and a fresh water tank).

The actual path of a vessel over the seabed.

Closest Point of Approach (CPA) is the minimum distance between two moving vessels. Time to Closest Point of Approach (TCPA) is the time remaining until that minimum distance is reached. Essential for collision avoidance.

The distance a vessel is off its intended track.

A crane-like device used for lifeboats.

The process of calculating a ship's current position by advancing a previously known position using its course steered and speed through the water, without factoring in external elements like current or wind.

A charge payable to the shipowner by the charterer in respect of failure to load or discharge the ship within the agreed allowed time (laytime).

A lifting device for cargo handling.

A monetary reward paid by the shipowner to the charterer if the ship is loaded or discharged in less time than the agreed laytime.

The total volume or weight of water displaced by a floating ship. By Archimedes' principle, this equals the total actual weight of the ship and everything on board.

A ship hull design and construction method where the bottom and sides of the ship have two complete layers of watertight hull surface, increasing safety immensely in case of grounding or collision.

Numbers painted on the side of a ship's bow, midships, and stern to indicate the vertical distance from the bottom of the keel to the waterline.

A commercial method of determining the weight of cargo loaded or discharged from a vessel by reading its draft marks before and after the operation, and calculating displacement changes using hydrostatic tables.

The vertical distance from the bottom of the keel to the waterline, representing how deep the ship sits in the water.

Material used to protect cargo.

A computer-controlled system to automatically maintain a vessel's position and heading by using its own propellers and thrusters against wind, waves, and ocean currents.

Electronic Chart Display and Information System. A geographic information system used for nautical navigation that complies with IMO regulations as an alternative to paper nautical charts.

Device to map underwater topography via sonar.

The calculated time a vessel is expected to arrive at a pilot station, port, or waypoint.

Unit of length equivalent to six feet.

Wreckage remaining afloat after a ship mishap.

Directional term meaning toward the bow (front) of the ship.

The destabilizing effect caused by liquids moving freely within partially filled (slack) tanks as a ship rolls. This virtual rise in the center of gravity reduces the ship's overall GM.

The vertical distance measured from the waterline to the upper deck (main deck/freeboard deck) of the hull. Essential for reserve buoyancy.

The kitchen and food prep area on a vessel.

The point on Earth directly beneath a celestial body at a given exact moment in time.

The practice of navigating along the arc of a great circle, which is the intersection of a sphere with a plane passing through its center. This represents the shortest possible distance between two points on the globe.

A nonlinear measure of a ship's overall internal volume (not weight). It forms the basis for manning regulations, safety rules, and port dues.

Compass operating on Earth's rotation, free from magnetism.

A graphical representation of a ships static stability, showing the righting lever (GZ) at various angles of heel.

The steel tube or pipe passing through the bow of the ship that the anchor chain passes through, securely housing the anchor when it is hauled up.

The direction in which the ship's bow is pointing.

The temporary inclination or tilt of a ship to one side, usually caused by external forces like wind or a high speed turn.

The vertical height of the observers eye above the sea level, used to correct sextant altitude for the curvature of the Earth (Dip).

A mechanical error in a sextant reading when the index and horizon mirrors are not perfectly parallel at zero.

The difference between the True Observed Altitude (Ho) and the Calculated Altitude (Hc) in celestial navigation.

Also known as the Marcq St. Hilaire method, a standard technique for reducing celestial sights to establish a line of position.

The central structural backbone of the hull.

A unit of speed equal to one nautical mile per hour.

The amount of time allowed in a voyage charter for the loading and unloading of cargo. Exceeding this triggers demurrage, while finishing early yields despatch.

A line constructed on a nautical chart representing a series of possible positions of a vessel. Two intersecting LOPs create a fix.

A widely used method of celestial sight reduction. It compares a Calculated Altitude (Hc) for an Assumed Position with the True Observed Altitude (Ho) to establish an intercept distance toward or away from a celestial body.

The distance between the center of gravity of a ship and its metacenter. A positive GM indicates initial static stability, meaning the ship will naturally return to an upright position after being heeled over.

Thick ropes, cables, or synthetic synthetics used to secure a ship to a dock, pier, buoy, or another ship. Includes head lines, stern lines, breast lines, and springs.

An annual publication containing astronomical data (ephemeris) used for celestial navigation, including GHA and Declination.

A nonlinear measure of the useful capacity of a ship (revenue-earning volume), calculated by deducting non-carnage spaces (engine room, crew quarters) from the Gross Tonnage.

The form factor and size limit for ships traveling through the original locks of the Panama Canal. Usually around 65,000 to 80,000 DWT for bulk carriers.

A comprehensive, berth-to-berth navigation plan developed to ensure the safe and efficient voyage of a vessel.

A cyber security or communication term referring to unauthorized traffic that rides along with authorized data streams.

A reference mark located on a ship's hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo.

The left-hand side of a vessel when facing forward. It is historically indicated by a red navigational light.

The inspection of foreign ships in national ports to verify that the condition of the ship and its equipment comply with the requirements of international regulations.

The determined location of a vessel on a chart, usually obtained by the intersection of two or more position lines (LOPs).

A line crossing all meridians of longitude at the same angle on the surface of the earth. It represents a path of constant bearing, which appears as a straight line on a Mercator projection chart but is not the shortest distance between two points.

Vessels designed to carry wheeled cargo, such as cars, trucks, semi-trailer trucks, trailers, and railroad cars, that are driven on and off the ship on their own wheels.

The process of selecting the most optimal path for a voyage, considering distance, weather, currents, and navigational hazards.

Terms describing ocean current vectors. Set is the true direction the current is flowing toward, while Drift is the speed of that current (usually measured in knots).

A precision optical instrument used by navigators to measure the angle between a celestial body and the visible horizon.

A specialized retail dealer who supplies required equipment, spare parts, provisions, and food for ships and their crew.

A documented plan developed under the ISPS Code to ensure the application of measures onboard the ship to protect persons and cargo.

A dedicated vertical tube extending from the main deck down to the absolute bottom of a tank, used by the crew to manually measure (sound) the exact depth of liquid contained within.

The hydrodynamic phenomenon where a vessel moving quickly through shallow water creates an area of lowered pressure under its hull, causing the ship to sink deeper into the water than its static draft.

A specific loading scenario for a vessel (e.g., Departure Full Load, Arrival Ballast) mathematically verified to meet IMO stability criteria.

The right-hand side of a vessel when facing forward. It is historically indicated by a green navigational light.

A dockworker or manual laborer primarily responsible for loading and unloading ships in a port.

A naval architecture term for the largest ship measurements capable of transiting the Suez Canal in a laden condition. Mostly used in reference to crude oil tankers of around 160,000 DWT.

An inexact unit of cargo capacity often used to describe the capacity of container ships and container terminals.

The estimated time remaining to reach the next waypoint or the final destination based on the current Speed Over Ground.

The empty space available in a partially filled tank or drum. Measured from the surface of the liquid to the very top ceiling reference point of the tank.

The vertical distance between the lowest part of the ship's hull (the keel) and the seabed. Accurately calculating UKC, including variables like squat, tide, and wave response, is critical to prevent grounding.

A very large crude oil tanker with a cargo carrying capacity ranging between 200,000 and 319,000 deadweight tons (DWT).

The maritime equivalent of the aviation "black box." A data recording system designed to collect data from various sensors on board the vessel for use in accident investigation.

A specific set of coordinates on a nautical chart used as a reference point for navigation and route planning.

A heavy-duty mechanical winch located on the forecastle (bow) of a ship, driven by an electric or hydraulic motor, used specifically to hoist and lower the ship's massive anchors.