Glossary of maritime terminology

a b c d e f g h i j k l m n o p q r s t u v w x y z


The A-frame is a lifting apparatus commonly found installed on the stern of pipe laying vessels, cable laying vessels, and offshore construction vessels.

Abandon Ship

"Abandon ship" is a maritime term used to inform the passengers and crew that they need to leave the ship immediately due to an emergency, such as the vessel being about to sink.

Able Bodied Seaman

An Able Bodied Seaman (also called an Able Seaman, or just AB) is a member of the Deck Department. They will have more than two years’ worth of experience and be expected to know the ins and outs of their job. An Able Seaman’s duties and responsibilities include standing watch / keeping lookout, cleaning and maintenance, conducting security rounds, supervising lower ranking deck crew, and assisting with operations such as docking, undocking, line handling and the loading and unloading of cargo.  


The accommodation area is the part of the ship in which the crew facilities are located. This includes the cabins and the crew mess (the dining area and place where crew members can hang out when they aren’t working.)

Accommodation Ladder

The accommodation ladder is a portable flight of stairs, with handrails, that is attached to the side of a vessel. This enables easy access between the dock or a smaller boat and the ship. The ladder is designed so that no matter what its angle of inclination, the steps will always be horizontal.

Accommodation Vessel

Some offshore workers sleep on their vessel or rig while others will decamp to a vessel moored nearby at the end of their working day or shift. These ships are known as accommodation vessels - or ACVs. They have living quarters, cabins, and usually dining rooms, and recreation facilities such as a gym.

Act of God

Usually described as 'force majeure' particularly in documents pertaining to Insurance, in maritime terminology, an Act of God is a natural event that is unpredictable and not able to be prevented by humans. Acts of God include floods, lightning, storms, tsunamis etc. 

Active Fin Stabilizers

Active fin stabilizers aim to reduce the rolling of a vessel in rough seas. This helps to provide greater stability and safety while reducing the negative impact on speed and fuel performance in adverse conditions. The fins are normally located near amidships on both sides (port and starboard) of the ship. They can be both retractable and non-retractable. Active fin stabilizers have long been a feature of passenger ships, such as cruise liners, however they are becoming increasingly popular on commercial cargo and container ships.   


ACV stands for air cushion vehicle - otherwise known as a hovercraft -  is supported mainly, or in its entirety, by a cushion of air. ACVs are supported both when in motion and at rest, meaning the air must be continuously generated.


Some offshore workers sleep on their vessel or rig while others will decamp to a vessel moored nearby at the end of their working day or shift. These ships are known as ACVs - or accommodation vessels. They have living quarters, cabins, and usually dining rooms, and recreation facilities such as a gym.

Added Mass

In shipping terms, when a vessel is in transit, the water that is moving around the hull creates a hydrodynamic force. Because a ship is a complexly shaped object, as opposed to a simple tube or sphere for example, an additional quantity of water is added to the water which has been displaced by the vessel’s movement to factor in the added mass.


Admeasurement is the formal measurement of a vessel in order to determine its capacity or tonnage.


Administration in freight terms refers to the government of the state under whose authority a vessel is operating. A ship flies a flag of a state and the administration is therefore the government of that state.


If a vessel is adrift, she is floating without being either steered or moored.


If a vessel is afloat, she is in the state of floating on water. She is not in dry dock on land or run aground.

Aframax Tanker

An aframax tanker is an oil tanker that has a DWT (deadweight) of between 80,000 and 120,000 metric tonnes. The name aframax comes from Average Freight Rate Assessment (AFRA). In shipping terms meaning, this is a rating system used for tankers coined by Shell Oil in 1954 in order to standardize the terms of shipping contracts.

Because of their size, aframax tankers are best suited to short- to medium-haul journeys, however their size is also to their advantage as they are able to serve the majority of the world’s ports, particularly those in regions that are unable to accommodate VLCC (very large crude carriers) and ULCC (ultra large crude carriers) tankers due to their smaller ports or lack of offshore oil terminals.   


Aft means towards or near to the vessel's stern.

Aft Peak

The aft peak is a compartment that is located aft (at, near, or towards the vessel’s stern) of the aftermost watertight bulkhead. 

Aft Peak Bulkhead

The aft peak bulkhead is the name for the first main transverse bulkhead forward of the stern. It must be kept watertight.

Aft Peak Tank

The aft peak tank is a water tank that is located in the right aft of a vessel. The tank will either be a designated freshwater tank or a ballast water tank which will be used to adjust the ship’s trim.

Aft Perpendicular

The aft perpendicular on a ship is an imaginary vertical line which is drawn between the forward side of the stern with the summer load waterline. However, it depends on the designer of the ship whether the aft perpendicular is drawn through the aft side of the rudder post or through the center-line of the rudder pintles. The length overall (LOA) is the distance between the fore and aft extreme points of the vessel and is the aft reference line for hydrostatic calculations.


The afterbody is the section of a vessel's hull which lies aft of midships. It encompasses the entire after half of the hull from the upper deck to the keel.

Afternoon Watch

The Afternoon Watch is the period of being on duty (AKA watch) that takes place onboard a vessel between 1200hrs and 1600hrs.

Agency Fee

An agency fee is a sum of money that is charged to the vessel by the ship's agent to compensate for any services that were received while the ship was in port.


Aground is the word used when a vessel is lying upon or touching shallow ground. The opposite of being afloat.


AHTS is short for anchor handling tug supply vessel - a tugboat that is used to tow and anchor offshore vessels, particularly in the oil and gas industry. If called upon, they will also provide emergency assistance.

Aids to Navigation

Aids to Navigation (AtoN) are anything that helps a vessel navigate more safely. They are charted marks and include items such as beacons, lighthouses, buoys, lights, and radio beacons.

Aids to Navigation Service Vessel

An aids to navigation service vessel is a ship or boat that carries special equipment in order to service, maintain and repair navigation aids such as automatic lighthouses, buoys, beacons, and lights.

Air Cushion Vehicle

An air cushion vehicle (ACV), otherwise known as a hovercraft, is supported mainly, or in its entirety, by a cushion of air. ACVs are supported both when in motion and at rest, meaning the air must be continuously generated.

Air Draft

The air draft (or air draught) is the vertical distance from the surface of the water (the waterline) to the highest fixed point on a vessel.

Air Lock

An air lock is a protected, enclosed area generally found on a gas carrier vessel that enables safe entrance between a dangerous gas zone and a gas safe space.

Air Lubrication

Air lubrication is a way to reduce hull friction by generating a layer of air between the underside of a vessel and the surface of the water. This increases a ship’s efficiency by reducing drag by up to 15%.

Air Resistance

Air resistance refers to a vessel’s resistance to motion that is caused by the air circulating around the part of the ship that is above water.

Air Trunks

Air trunks are a part of a vessel’s hull that either contain air ducts as well as other lines such as pipes and cables, or are themselves used to conduct air.


AIS stands for Automatic Identification System - an automated tracking system that is used to identify vessels assist in target tracking simplify information exchange and provide additional information to boost situational awareness.

Alarm and Monitoring System

The ship’s Alarm and Monitoring System (AMS) is a crucial piece of equipment for ensuring that all onboard operations are conducted safely. The system's main function is to keep the officers and engineers informed and updated by detecting any issues and alerting them to the vessel’s status and critical conditions. 

Aldis Lamp

The Aldis lamp (also called a signal lamp or Morse lamp) is a hand-held electric lamp which is normally found on the bridge wing of a vessel. It is used to signal Morse code messages via flashing light between ships of all types, including naval and commercial.


Alfa stands for the letter A in the International Radiotelephony Spelling Alphabet, which is most often referred to as the NATO Phonetic Alphabet or simply the Phonetic Alphabet. This is the most commonly used group of code words used to clearly communicate the letters of the Roman alphabet, particularly over the radio and is essential in helping seafarers give and receive messages, orders and instructions clearly and correctly.

Note that Alfa is intentionally spelled ‘incorrectly’ to avoid any confusion caused by its original spellings - i.e. Alpha - being mispronounced

All Hands

All hands refers to the entire ship’s company, including all crew members as well as officers. Most commonly heard in the expression "All hands on deck.”


An alleyway is the name given to any corridor onboard a vessel that connects one area of the accommodation to another.


Allision is the name given to the act of a moving ship striking or colliding with a stationary object - such as a dock. Not to be confused with collision which generally refers to two vessels colliding with one another.


A vessel is alongside when she is positioned side by side with another ship, or a jetty, wharf or dock.


Amidships refers to the middle of a ship either longitudinally or laterally. In ship building amidships is located in the middle of the length of the vessel.


 AMS is the abbreviation for Alarm and Monitoring System - a crucial piece of equipment for ensuring that all onboard operations are conducted safely. The system's main function is to keep the officers and engineers informed and updated by detecting any issues and alerting them to the vessel’s status and critical conditions.  


An anchor is a heavy object or device that is attached to a cable, chain or rope, and is shaped, typically with barbed flukes, so that it grips the sea bed. The anchor holds a ship (or other floating structure) in her desired position regardless of wind and current.

Anchor Ball

The anchor ball is a round black ball which is displayed at the front of a vessel to show that the ship is anchored.

Anchor Buoy

The anchor buoy is a small buoy that is sometimes used to mark the position of the anchor when it's on the bottom. The anchor buoy is fastened to the anchor's crown by a buoy rope and normally either painted red (port) or green (starboard).

Anchor Cable

The anchor cable (or anchor rode, anchor chain, or anchor rope) is attached at one end to the vessel and at the other end to the anchor. 

Anchor Chain

The anchor chain (or anchor rode, anchor cable, or anchor rope) is attached at one end to the vessel and at the other end to the anchor. 

Anchor Handling Tug

An anchor handling tug is a type of tugboat that is used to move anchors, as well as for towing drilling vessels, lighters and other similar vessels.

Anchor Lights

Anchor lights are the lights that a vessel must display when she is at anchor.

Anchor Pocket

The anchor pocket is a recess in the bow of a ship that houses a stockless anchor.

Anchor Rode

The anchor rode (or anchor chain, anchor cable, or anchor rope) is attached at one end to the vessel and at the other end to the anchor. 

Anchor Rope

The anchor rope (or anchor rode, anchor cable, or anchor chain) is attached at one end to the vessel and at the other end to the anchor. 

Anchor Watch

The anchor watch is when an Officer remains on deck at night when the ship is at anchor, to safeguard the vessel. This can mean everything from staying alert to intruders, to making sure the anchor is not dragging and moving the ship, to keeping an eye out for other vessels who may be dragging or sailing too close.

Anchor Windlass

An anchor windlass is a mechanical device that operates on a pulley system and is used to raise and lower the anchor and chain down to, and up from, the sea bed. This system consists of a barrel with a chain or cable wound around it and is operated using a belt or crankshaft, either manually, or by motor.   


Anchorage is the fee charged by a port or harbor to allow a vessel to moor there.

Anti-Exposure Suit

 In maritime terms, an anti-exposure suit (also called an exposure suit) is a garment designed to protect the wearer from an extreme environment. For example, from wet and cold environments found at sea, specifically in evacuation or rescue operations, or in diving. Depending on the type of suit and the situation it has been designed for, the garment may provide buoyancy, total isolation from the environment, or thermal insulation.  

Anti-Fouling Paint

Anti-fouling paint is a type of paint that is manufactured using specific agents to prevent the growth and attachment of organisms on a vessel’s hull.

Anti-Fouling System

An Anti-Fouling System is a device, treatment, paint or coating that controls, or prevents, the attachment of organisms on a vessel’s hull.

Anti-Heeling System

An Anti-Heeling System is used during cargo operations - i.e. during the loading and unloading of freight - to ensure that the ship’s heeling angle is kept to a minimum. This is important as excessive heeling could result in rolling cargo being damaged, containers getting jammed in cell guides or ramps being twisted.

Anti-Rack Spacer System

An Anti-Rack Spacer System is a system that can be used to connect two 20-foot shipping containers to create one single 40-foot container.

Anti-Roll Tank

An anti-roll tank is a tank that is fitted onto a vessel with the aim of improving that tank's response to roll motion. The rate of water transferred to the port side of the tank to the starboard side is slowed by baffles, whilst the tank itself is designed so that a greater quantity of water remains on the ship’s higher side.


An appendage is any part of a ship that protrudes from the hull below the waterline. This includes propellers, the rudder, shafts, bilge keels, struts, and sonar domes.


The apron is an area that is directly in front or behind a wharf shed onto which cargo is lifted. The cargo is unloaded or loaded onto a vessel from the front apron and into and out of trucks or railroad cars from the rear apron.


ARPA stands for Automatic Radar Plotting Aid - a computerized add-on feature to the radar. ARPA identifies the ship’s course and speed and a target's course and speed and calculates the collision avoidance data. This makes it much easier for humans rather than calculating the data themselves.


Arrest or ship arrest refers to a court order in which a vessel is ‘arrested’ and held under state authority in a port in the face of a pending present or future claim that relates to the vessel. The reasons for a ship’s arrest can be due to anything from a claim by creditors to the vessel’s unseaworthiness.

Articles of Agreement

The Articles of Agreement is the document which contains all information relating to the maritime terms of agreement between the Master (Captain) of the vessel and the crew. 

Assembly Station

A ship’s assembly station is an area in which passengers and crew must meet in the event of an alarm, emergency or announcement.


Astern can variously mean behind a ship, located at or towards the stern of a ship, or the act of a ship moving backwards.


Generally used to describe cargo, athwartships is to be in a position across a vessel from side to side at right angles to the keel.


Similar to an atrium in land-based architecture, this is a public area with a high roof. In nautical terms, the height spans three or more open decks.

Auto Container

An auto container is a shipping container used for the transportation of cars and other vehicles.

Auto Mooring System

An Auto Mooring System makes the mooring and unmooring of vessels a faster process, reducing the time spent in port and therefore fuel consumption and emissions. The system is controlled remotely from the bridge of the ship, or by a location on shore. 

Automatic Identification System (AIS)

 An Automatic Identification System (AIS) is a navigational aid and automated tracking system that is used for the identification of vessels and navigational marks. It displays other vessels in the vicinity of a ship whilst also showing the ship it is located on to other vessels with AIS in that area. AIS is a broadcast transponder system that operates in the VHF mobile maritime band, autonomously and continually.  

Automatic Radar Plotting Aid (ARPA)

An Automatic Radar Plotting Aid (ARPA) is a marine radar technology designed to replace the manual plotting of targets. The ARPA uses radar contacts to calculate the course speed and closest point of approach (CPA) to various tracked objects. This enables whoever is steering or navigating a vessel to monitor the screen and take action if there is a potential chance of collision with that object.


 An autopilot (or automatic pilot) is a self-steering device system used for automatic navigation. They come in varying degrees of complexity and sophistication although any autopilot should be able to maintain a vessel on a pre-set compass course. More advanced autopilots gather data from the ship’s instruments or connect to GPS receivers. The system will be able to tell the difference between the vessel’s ordered course and the actual course and will automatically adjust the rudder so that it moves to an angle that is proportional to the discrepancy.   


A vessel’s auxiliaries are equipment such as motors, engines, winches and pumps etc. They have a part to play in the running of the vessel alongside the main propulsive machinery - such as boilers and engines on a steam installation.

Auxiliary Boiler

The auxiliary boilers on a vessel are boilers that supply the steam that enables the running of essential machinery and equipment such as motors, engines, winches and pumps. Unlike the main propulsion boiler, they do not have anything to do with the actual propulsion of the ship.

Auxiliary Crane Shp

An auxiliary crane ship is usually a converted container ship. These vessels are equipped with cranes that are able to lift shipping containers and other cargo and are used to unload goods from their own holds as well from other vessels. They are typically used at ports and terminals which don’t have their own cargo handling capabilities.


Avast is a nautical term. It is an order to immediately stop doing something.


Awash is a term used to describe it when a vessel is so low in the water that the water is washing across the deck.


Aweigh is a term used to describe the moment when the anchor has just been lifted from the seabed.