Maritime glossary

290 terms indexed. Browse by letter or category.

• 'Tween Deck
  An intermediate deck between the upper and lower decks of a cargo hold, providing separate stowage tiers for break-bulk cargo.
• 15 ppm Bilge Alarm
  An automatic alarm fitted to an oily water separator that stops overboard discharge when oil content exceeds 15 parts per million.
• Able Seaman (AB)
  Certified deck rating with a minimum of 18 months sea service, competent in watchkeeping, mooring, and cargo handling.
• AIS Class A
  The mandatory AIS transponder fitted on SOLAS ships transmitting vessel data at regular intervals and responding to interrogations.
• AIS Class B
  A lower-power AIS transponder used by smaller non-SOLAS vessels, transmitting position and identity data at reduced reporting rates.
• Anchor Handling Tug Supply Vessel (AHTS)
  An offshore support vessel designed to tow and position mobile drilling rigs and handle anchors in deepwater operations.
• Anchorage
  A designated area with suitable holding ground where a vessel anchors to wait for a berth, tide, or clearance.
• Angle of Loll
  The angle at which a vessel with negative initial stability comes to rest on her side as she cannot return to upright.
• Annual Survey
  A classification inspection conducted each year to confirm that a vessel's hull and equipment remain in a satisfactory condition.
• Automatic Identification System (AIS)
  VHF transponder system that automatically broadcasts vessel identity, position, course, and speed to nearby ships and shore stations.
• Auxiliary Engine (AE)
  A diesel generator engine providing electrical power for shipboard systems independent of the main engine.
• Azimuth
  The angular bearing of a celestial body measured clockwise from true north, used to check compass error.
• Azimuth Thruster
  A propulsion unit that can rotate 360 degrees, providing both thrust and steering without a conventional rudder.
• Ballast Water Management Convention (BWM Convention)
  The 2004 IMO convention requiring ships to manage ballast water to prevent transfer of invasive aquatic species between regions.
• Ballast Water Record Book (BWRB)
  A mandatory log recording all ballast water uptake, treatment, exchange, and discharge operations under the BWM Convention.
• BAPLIE
  An EDI message format conveying the stowage positions of all containers aboard a vessel between terminals and ship operators.
• Basic Safety Training (BST)
  Mandatory STCW training covering personal survival, fire prevention, first aid, and personal safety for all seafarers.
• Bay Plan
  A grid diagram showing every container slot in a vessel's cross-section by bay, row, and tier with container data.
• Bearing
  The horizontal direction of one point from another, expressed in degrees from 000° to 359°.
• Beaufort Scale
  An empirical scale from 0 to 12 that relates wind speed to observed sea surface conditions and wave heights.
• Berth
  A designated position at a wharf or quay where a vessel moors to load or discharge cargo or embark passengers.
• Bilge
  The lowest interior space of a vessel where leakage, condensation, and drainage water collects; must be pumped out regularly.
• Bill of Lading (B/L)
  A legal document issued by a carrier acknowledging receipt of cargo for shipment, serving as a receipt, title document, and contract of carriage.
• Bosun
  Senior unlicensed deck rating responsible for the upkeep of deck equipment, mooring gear, and supervision of the deck crew.
• Bow Thruster
  A transverse propulsion unit fitted in a tunnel through the bow section to improve low-speed manoeuvrability in port.
• Break Bulk
  Non-containerised cargo loaded individually as bags, bales, crates, or drums rather than in standard containers.
• Bridge Alarm
  An alarm system on UMS vessels that channels all critical engine room and safety alarms to the navigating bridge when the engine room is unmanned.
• Bridge Log
  A watchkeeping record maintained on the bridge detailing courses steered, speed, weather conditions, and watch handovers.
• Broken Stowage
  The wasted space in a cargo hold that cannot be utilised due to the shape or packaging of the cargo being carried.
• Bulk Carrier
  A single-deck cargo vessel designed to carry unpackaged dry bulk cargoes such as grain, coal, iron ore, or fertiliser.
• Bunker
  Fuel oil carried aboard and consumed by a ship's main and auxiliary engines; also refers to the act of taking on fuel.
• Bunkering
  The operation of taking fuel oil aboard a vessel, requiring careful monitoring of quantities, trim, and pollution prevention measures.
• Cadet
  A trainee officer serving aboard ship as part of an approved maritime academy programme to gain sea service for certification.
• Call Sign
  An ITU-assigned alphanumeric identifier used to identify a vessel during radio communications.
• Capstan
  A vertical-axis powered drum on deck used to heave in mooring lines or warping lines.
• Cargo Control Room Operator (CCR Operator)
  An officer or rating on a tanker or bulk carrier who monitors and controls cargo loading, discharging, and ballasting operations from a centralised control room.
• Cargo Pump
  A large-capacity pump on a tanker used to discharge liquid cargo from cargo tanks to shore or to another vessel.
• Celestial Navigation
  The art and science of determining a vessel's position by measuring the altitudes of celestial bodies with a sextant.
• Certificate of Registry
  An official document issued by the flag state confirming the vessel's registration, nationality, and ownership details.
• Charter Party (C/P)
  A contract between a shipowner and a charterer for the hire of a vessel or cargo space, setting out terms and conditions of the voyage.
• Chemical Tanker
  A tanker built to carry noxious liquid substances in bulk, constructed to IBC Code standards for cargo containment.
• Chief Engineer (C/E)
  The senior engineer officer responsible for the operation, maintenance, and safety of all machinery and technical systems aboard.
• Chief Mate (C/O)
  The officer second in command to the master, responsible for cargo operations, stability, deck maintenance, and crew safety.
• Chronometer
  A precision timekeeping instrument used in celestial navigation to provide accurate GMT for the calculation of longitude.
• Classification Society
  A non-governmental organisation that establishes and verifies structural and mechanical standards for ship construction and maintenance.
• Clearing Line
  A bearing or line on the chart that, when maintained, keeps a vessel clear of a specific hazard such as a shoal or reef.
• Cold Lay-up
  A long-term idling of a vessel with systems shut down and crew reduced to a minimum, used when reactivation is uncertain.
• Combination Ladder
  A pilot boarding arrangement combining a pilot ladder below with an accommodation ladder above to accommodate height differences.
• Company Security Officer (CSO)
  The shore-based person designated by a company to be responsible for developing and implementing its Ship Security Plans under the ISPS Code.
• Compass
  Instrument indicating direction relative to magnetic north or true north, fundamental to ship navigation.
• Compass Bearing
  A bearing measured by a ship's compass, requiring correction for both variation and deviation to obtain a true bearing.
• Container Ship
  A cargo vessel designed to carry ISO standard intermodal containers stacked in cells below deck and in tiers on deck.
• Controllable Pitch Propeller (CPP)
  A propeller whose blade pitch can be varied in service, allowing speed and thrust control without changing engine rotation direction.
• Crankcase
  The lower enclosed section of an engine housing the crankshaft, connecting rods, and bearing lubrication system.
• Crude Oil Washing (COW)
  A tank cleaning method using crude oil cargo as the washing medium to dissolve and remove waxy residue from tank surfaces.
• Cruise Ship
  A large passenger vessel offering multi-day voyages with onboard leisure facilities as the primary commercial product.
• Danger Angle
  A horizontal or vertical sextant angle that, when not exceeded, ensures a vessel remains clear of a coastal hazard.
• Dangerous Goods (DG)
  Cargo classified under the IMDG Code as posing risks to health, safety, property, or the environment during sea transport.
• Dead Reckoning (DR)
  Calculating current position using a known past position, then advancing it using speed, course, and elapsed time.
• Deadweight (DWT)
  The total weight a vessel can carry including cargo, fuel, water, stores, and crew, measured in metric tonnes.
• Deck Cadet
  A trainee deck officer undertaking approved sea service under a maritime academy programme to qualify for an OOW certificate.
• Deck Cargo
  Cargo stowed on the open weather deck and exposed to the sea environment, requiring additional securing and weatherproofing.
• Deck Log
  The official daily record of the ship's position, weather, incidents, crew changes, and navigational events kept by deck officers.
• Deep Water Route
  A route within defined limits, surveyed and confirmed to have sufficient depth, designated for use by vessels requiring deep draught.
• Demurrage
  A penalty charge payable by the charterer when a vessel is kept at the loading or discharging berth beyond the agreed laytime.
• Designated Person Ashore (DPA)
  The ISM Code-required company contact point with direct access to the highest management level, responsible for safety and pollution prevention oversight.
• Deviation
  The error in a magnetic compass caused by the ship's own magnetic field, varying with the vessel's heading.
• Deviation Card
  A tabulated record of a magnetic compass's deviation on successive headings, prepared after compass adjustment or swing.
• Digital Selective Calling (DSC)
  A standard for transmitting pre-defined digital messages over VHF/MF/HF radio to initiate distress, urgency, or routine calls.
• Dispatch
  A payment made by the shipowner to the charterer for completing loading or discharging operations before the agreed laytime expires.
• Displacement
  The total mass of water displaced by a floating vessel, equal to the combined weight of the hull, machinery, cargo, and stores.
• Docking Survey
  An in-water or drydock inspection of the hull, rudder, propeller, and sea valves required by classification societies every two to five years.
• Document of Compliance (DOC)
  A certificate issued to a shipping company confirming its Safety Management System meets ISM Code requirements.
• Draft
  The vertical distance between the keel and the waterline, determining the minimum water depth needed for safe navigation.
• Drydock
  A scheduled period when a vessel is taken out of service and placed in a dry facility for hull inspection, maintenance, and repairs.
• Dunnage
  Timber, mats, or other material placed under or between cargo to protect it from moisture, damage, and shifting.
• Dynamic Positioning (DP)
  A computer-controlled system that automatically maintains a vessel's position and heading using thrusters, without anchoring.
• Dynamic Positioning Operator (DPO)
  A certificated officer qualified to operate and monitor a vessel's dynamic positioning system during offshore operations.
• Electro-Technical Officer (ETO)
  A certificated officer responsible for the maintenance and repair of electrical, electronic, and automation systems aboard.
• Electronic Chart Display and Information System (ECDIS)
  A navigation information system that displays ENCs and vessel position, accepted as a replacement for paper charts under SOLAS.
• Emergency Escape Breathing Device (EEBD)
  A self-contained breathing device providing approximately 10 minutes of breathable air to escape a smoke-filled space.
• Emergency Fire Pump
  A self-contained fire pump located outside the machinery space, capable of supplying fire mains if the main pumps are disabled.
• Emergency Generator
  A self-contained standby generator automatically supplying essential electrical power to safety systems if the main supply fails.
• Emergency Position Indicating Radio Beacon (EPIRB)
  A satellite beacon that transmits a distress signal with vessel identity and position to the Cospas-Sarsat system when activated.
• Emission Control Area (ECA)
  A sea area designated under MARPOL Annex VI where stricter limits on sulfur and NOx emissions from ships apply.
• Engine Cadet
  A trainee engineer officer undertaking approved sea service as part of an engineering degree programme to qualify for a watchkeeping certificate.
• Engine Log
  The official daily record maintained by the engine department of machinery performance, fuel consumption, and maintenance events.
• Equasis
  A free public database providing safety-related information on commercial vessels including inspection history, class, and owner details.
• Estimated Position (EP)
  A position obtained by advancing a known fix using course and speed while applying estimated leeway and current allowances.
• Exclusive Economic Zone (EEZ)
  A sea zone extending up to 200 nautical miles from a coastal state's baseline where it has sovereign rights over resources.
• Exhaust Gas Cleaning System (EGCS)
  A device fitted in the exhaust line that removes sulfur oxides from engine gases, allowing use of high-sulfur HFO under IMO 2020.
• Fender
  A cushioning device of rubber, foam, or rope placed between a vessel and a berth or another vessel to prevent damage.
• Fire Drill
  A mandatory shipboard exercise practising the crew's response to a fire emergency, required at least monthly under SOLAS.
• Fire Safety Systems Code (FSS Code)
  IMO code detailing international requirements for fire detection, suppression, and firefighting equipment on SOLAS ships.
• Fitter
  A skilled engine room rating who performs mechanical repairs and maintenance on machinery, pipework, and deck equipment.
• Fix
  A confirmed vessel position established by two or more simultaneous position lines from observed bearings, ranges, or electronic navaids.
• Fixed Pitch Propeller (FPP)
  A propeller with blades cast at a fixed angle to the hub; speed and direction are changed by varying engine rpm and rotation.
• Flag of Convenience (FOC)
  Registration of a vessel in a country offering lower taxes or less strict regulations than the owner's home nation.
• Flag State Inspection
  An official inspection of a vessel carried out by or on behalf of the flag administration to verify compliance with its regulations.
• Fleet Broadband (FBB)
  An Inmarsat satellite broadband service providing high-speed voice and data communications on mobile maritime terminals.
• Fleet Manager
  A senior shore-side executive responsible for the commercial, operational, and crewing management of a group of vessels.
• Floating Dock
  A pontoon structure that can be submerged to receive a vessel then raised to lift it clear of the water for repair work.
• Floating Production Storage and Offloading (FPSO)
  A floating vessel used by the offshore oil and gas industry for production, processing, storage, and offloading of hydrocarbons.
• Floating Storage and Offloading (FSO)
  A stationary floating vessel used to store crude oil or petroleum products at offshore fields pending transfer to shuttle tankers.
• Forty-foot Equivalent Unit (FEU)
  Standard unit of cargo capacity equivalent to one 40-foot ISO shipping container, equal to two TEU.
• Four-Stroke Engine
  An internal combustion engine requiring four piston strokes per cycle, widely used as medium-speed auxiliary and propulsion engines.
• Fourth Engineer (4/E)
  The most junior watchkeeping engineer officer, gaining experience under supervision of senior engineers.
• Free Surface Effect (FSE)
  The virtual reduction in GM caused by a liquid surface in a partially filled tank that moves as the ship heels, reducing stability.
• Freeboard
  The vertical distance from the waterline to the main deck edge, indicating reserve buoyancy and load line compliance.
• Fresh Water Generator (FWG)
  A distillation unit using main engine jacket water waste heat to evaporate and condense seawater into fresh water at sea.
• Gangway
  A portable access ladder or bridge rigged over the ship's side to allow persons to embark and disembark safely.
• Garbage Record Book (GRB)
  A mandatory log recording all garbage disposal and incineration operations on board, required under MARPOL Annex V.
• General Cargo Ship
  A multipurpose vessel with cargo holds, tween decks, and derricks or cranes, designed to carry a variety of break-bulk and unitised cargoes.
• Generator Set (genset)
  A diesel-electric power unit installed in a ship's hold or on deck to supply electrical power to reefer containers.
• Global Maritime Distress and Safety System (GMDSS)
  An internationally agreed set of safety procedures and communications equipment required on SOLAS ships for distress and safety.
• Global Positioning System (GPS)
  US satellite-based radionavigation system providing position, velocity, and time data worldwide to marine and other users.
• GMDSS Sea Area A1 (Area A1)
  An area within range of at least one VHF DSC coast station providing continuous alerting coverage, typically within 20–50 miles of shore.
• GMDSS Sea Area A2 (Area A2)
  An area beyond A1 but within MF DSC continuous coverage, typically up to 400 nautical miles from shore.
• GMDSS Sea Area A3 (Area A3)
  An area beyond A1 and A2 within coverage of an Inmarsat geostationary satellite, covering most ocean areas between latitudes 70°N and 70°S.
• GMDSS Sea Area A4 (Area A4)
  The polar sea areas beyond GMDSS Area A3, not covered by geostationary satellites, where HF radio is used for distress alerting.
• Graving Dock
  A watertight basin into which a vessel is floated, then dewatered, allowing access to the entire underwater hull for inspection and repair.
• Great Circle
  The shortest route between two points on a sphere, formed by the intersection of the sphere and a plane through its center.
• Gyrocompass
  A compass using a gyroscope to find geographic north, unaffected by magnetic fields; mandatory on most large vessels.
• Hague-Visby Rules
  The amended 1924 Hague Rules governing carrier liability for cargo under bills of lading, widely incorporated into national law.
• Hamburg Rules
  The 1978 UN convention on the carriage of goods by sea, placing greater liability on carriers than the Hague-Visby Rules.
• Hawser
  A large rope or cable used for mooring or towing a vessel, typically greater than 25mm in diameter.
• Heavy Fuel Oil (HFO)
  Residual fuel oil with high viscosity and sulfur content, historically the primary bunker fuel for ocean-going vessels.
• Hot Lay-up
  A temporary idling of a vessel with full crew and systems maintained, enabling rapid return to service when market conditions improve.
• Hull Cleaning
  Removal of fouling organisms and paint buildup from the underwater hull to restore vessel speed and fuel efficiency.
• Hurricane
  A tropical cyclone in the Atlantic or eastern Pacific with sustained winds of 64 knots or more on the Beaufort scale.
• Immersion Suit
  A watertight thermal protective suit worn in cold water abandonment that significantly extends survival time.
• IMO Number
  A unique seven-digit identifier assigned to a ship for life, used to track its history regardless of flag, owner, or name changes.
• Inert Gas System (IGS)
  A system supplying inert gas (flue gas or nitrogen) to tanker cargo tanks to maintain an oxygen-deficient atmosphere and prevent explosion.
• Innocent Passage
  The right of foreign ships to navigate through a coastal state's territorial sea continuously and without prejudice to its peace or security.
• Inshore Traffic Zone (ITZ)
  The water between a traffic separation scheme and the adjacent coast, normally reserved for local and small craft traffic.
• Intercept
  In celestial navigation, the difference in minutes of arc between the observed altitude and the calculated altitude, used to plot a position line.
• Intermediate Fuel Oil (IFO)
  A blend of heavy residual and distillate fuel oil with viscosity typically 180 or 380 cSt, used as main engine bunker.
• Intermediate Survey
  A classification survey conducted midway through the five-year special survey cycle, typically around the second or third year.
• International Association of Classification Societies (IACS)
  A body of twelve major classification societies that collectively establish and promote uniform technical standards for ship construction and maintenance.
• International Convention for the Prevention of Pollution from Ships (MARPOL)
  The main international convention covering prevention of pollution of the sea by ships from operational and accidental causes.
• International Convention for the Safety of Life at Sea (SOLAS)
  The primary IMO convention setting minimum safety standards for ship construction, equipment, and operation.
• International Maritime Dangerous Goods Code (IMDG)
  IMO code governing the safe carriage of hazardous materials by sea, covering classification, packing, marking, and stowage.
• International Regulations for Preventing Collisions at Sea (COLREGs)
  IMO rules prescribing conduct of vessels to prevent collisions, including lights, shapes, sound signals, and steering rules.
• International Safety Management Code (ISM Code)
  IMO code requiring shipping companies to establish a Safety Management System to ensure safe ship operation and pollution prevention.
• International Ship and Port Facility Security Code (ISPS Code)
  IMO code mandating security plans, officers, and assessments for ships and port facilities to prevent terrorism and unlawful acts.
• Intertropical Convergence Zone (ITCZ)
  A band of low pressure near the equator where trade winds converge, producing persistent convective weather and squalls.
• Jacking Gear
  A reduction-gear device coupled to the engine flywheel used to slowly turn the engine by hand or motor for inspection.
• Laid Up
  The status of a vessel taken out of active trading and moored or anchored in a sheltered location while awaiting employment.
• Lashing
  Chains, wire, or webbing straps used to secure cargo on deck or in holds against movement during sea passage.
• Lashing Rod
  A threaded steel rod used in combination with turnbuckles to secure containers and deck cargo against movement at sea.
• Laytime
  The agreed time allowed in a charter party for loading or discharging cargo; excess time results in demurrage charges.
• Leading Line
  Two charted objects in line that define a safe course into or within a port, keeping the vessel clear of hazards.
• Life-Saving Appliances Code (LSA Code)
  IMO code specifying performance standards and testing for all life-saving appliances required by SOLAS Chapter III.
• Lifeboat
  A survival craft capable of sustaining life at sea, required on all SOLAS vessels and capable of being launched under adverse conditions.
• Liferaft
  An inflatable or rigid survival craft stowed on deck and launched by hand or hydrostatic release if the vessel sinks.
• Light Ship
  A vessel's weight when fully equipped with permanent fixtures but without cargo, fuel, ballast, stores, or crew on board.
• List
  A permanent transverse inclination of a vessel caused by an uneven distribution of weights across the ship.
• LNG Carrier
  A purpose-built vessel carrying liquefied natural gas in insulated cargo tanks at approximately −163°C.
• Load Line Certificate
  A certificate assigned by the flag state or classification society specifying the minimum freeboard and maximum loading depth for each zone.
• Loading Master
  A terminal representative who supervises the safe conduct of cargo transfer operations between shore installation and vessel.
• Long Range Identification and Tracking (LRIT)
  A mandatory satellite-based tracking system requiring SOLAS ships to transmit identity and position to flag and port state authorities.
• Loxodrome
  A line on the earth's surface crossing all meridians at the same angle, synonymous with a rhumb line course.
• LPG Carrier
  A gas tanker designed to carry liquefied petroleum gases such as propane or butane under pressure or refrigeration.
• Magnetic Bearing
  A bearing measured clockwise from magnetic north, requiring correction for variation to obtain a true bearing.
• Magnetic Compass
  A compass that aligns with Earth's magnetic field to indicate magnetic north; required as backup on all SOLAS vessels.
• Main Engine (ME)
  The primary propulsion engine driving the ship's propeller shaft, typically a large slow-speed two-stroke diesel on cargo ships.
• Mandatory Pilotage
  A legal requirement in certain ports or waterways that a licensed pilot must be employed to navigate a vessel through that area.
• Marine Diesel Oil (MDO)
  A distillate fuel oil with low sulfur content, used in auxiliary engines and during port operations where ECA rules apply.
• Marine Superintendent
  A senior shore-side manager responsible for the nautical operations, safety, and compliance of vessels in a company fleet.
• Maritime Labour Convention 2006 (MLC)
  ILO convention establishing minimum working, living, and social security standards for seafarers worldwide.
• MARPOL Annex I
  The annex of MARPOL regulating prevention of pollution by oil, covering operational discharges and accidental spills from ships.
• MARPOL Annex II
  The annex of MARPOL controlling discharge of noxious liquid substances carried in bulk, applicable to chemical tankers.
• MARPOL Annex V
  The annex of MARPOL governing disposal of garbage from ships, prohibiting most plastics discharge into the sea.
• MARPOL Annex VI
  The annex of MARPOL setting limits on sulphur oxides, nitrogen oxides, and other air pollutant emissions from ships.
• Mast Riser
  A large-diameter high-velocity vent pipe fitted to a tanker's mast to discharge cargo vapours safely above ignition sources.
• Master
  The certificated officer in overall command of a vessel, legally responsible for the safety of the ship, crew, cargo, and environment.
• Material Safety Data Sheet (MSDS)
  A document providing information on the hazards, handling precautions, and emergency procedures for a chemical or dangerous cargo.
• Mercator Sailing
  A method of solving rhumb line problems using the properties of a Mercator chart to find course and distance between positions.
• Metacentric Height (GM)
  The vertical distance between the centre of gravity (G) and the metacentre (M), the primary indicator of a vessel's initial stability.
• METAREA
  One of twenty-one geographic areas for which meteorological services co-ordinate the broadcast of marine weather forecasts.
• MMSI Number (MMSI)
  A nine-digit Maritime Mobile Service Identity used to identify a ship's radio and AIS transmissions uniquely.
• Moment to Change Trim 1 cm (MCT1cm)
  The trimming moment in tonne-metres needed to alter a vessel's trim by one centimetre, used in stability calculations.
• Monsoon
  A seasonal reversal of prevailing winds affecting the Indian Ocean and western Pacific, bringing heavy rainfall on its wet phase.
• Mooring
  Securing a vessel to a berth, buoy, or anchor using lines, chains, or anchors to keep it stationary.
• Motorman
  An engine room rating who assists engineers with machinery operation, maintenance, and watchkeeping duties.
• Muster Station
  A designated assembly point where crew and passengers gather when an emergency alarm is sounded prior to abandoning ship.
• NAVAREA
  One of sixteen geographic sea areas defined by IMO/IHO for the co-ordination of worldwide navigational warning broadcasts.
• Navigational Telex (NAVTEX)
  An automated medium frequency broadcast system transmitting navigational warnings, weather forecasts, and search and rescue notices.
• Notice of Readiness (NOR)
  A formal written notice given by the master to the charterer or shipper that the vessel has arrived and is ready to load or discharge.
• Oil Discharge Monitoring and Control System (ODMCS)
  Equipment on oil tankers that continuously monitors the oil content and flow rate of overboard discharges to ensure MARPOL compliance.
• Oil Mist Detector (OMD)
  A crankcase monitoring device that samples air from each crankcase compartment and alarms if oil mist concentration reaches explosive levels.
• Oil Record Book (ORB)
  A mandatory log in which all oil-related operations including bilge pumping and bunkering must be recorded under MARPOL Annex I.
• Oiler
  An engine department rating who lubricates machinery, maintains oil records, and stands engine room watches.
• Oily Water Separator (OWS)
  Equipment that separates oil from bilge water to reduce oil content to 15 ppm before overboard discharge under MARPOL.
• Ordinary Seaman (OS)
  Entry-level unlicensed deck rating assigned general duties under the supervision of ABs and the bosun.
• Parallel Index (PI)
  A radar technique using lines parallel to the course line to monitor closest approach to a fixed radar target.
• Paris Memorandum of Understanding (Paris MOU)
  A regional port state control arrangement covering European and North Atlantic waters with 27 member maritime authorities.
• Pilot
  A licensed navigational specialist employed to guide a vessel through a specific port, harbour, or restricted waterway.
• Pilot Boarding Point (PBP)
  A designated position at sea where a pilot boards or disembarks a vessel before proceeding to or after leaving a port.
• Pilot Ladder
  A rope side ladder rigged overside to enable a pilot to board or disembark from a ship at sea.
• Pilotage
  The navigational service provided by a licensed pilot who boards a vessel to guide it through a port or restricted waterway.
• Platform Supply Vessel (PSV)
  An offshore supply vessel designed to carry deck cargo, dry bulk, liquid mud, and fuel to offshore platforms and rigs.
• Port Captain
  A company representative ashore, usually a former master, who assists vessels in port with local knowledge, clearances, and operational support.
• Port State Control (PSC)
  Inspection regime where a coastal nation's surveyors inspect foreign vessels in its ports for compliance with international conventions.
• Port State Control Inspection (PSC inspection)
  An examination of a foreign-flagged vessel in port by officers of the port state to verify compliance with international conventions.
• Precautionary Area
  A routing measure where vessels must navigate with caution due to converging traffic lanes or hazardous conditions.
• Pressure/Vacuum Valve (P/V valve)
  A safety valve on a cargo tank vent that opens at set over- or under-pressure limits to protect the tank structure.
• Product Tanker
  A tanker designed to carry refined petroleum products such as gasoline, jet fuel, and diesel in coated or stainless steel tanks.
• Pumpman
  A specialised deck or engine rating on tankers responsible for operating cargo and ballast pumps and maintaining pump rooms.
• Purifier
  A centrifugal separator that removes water and solid contaminants from fuel or lubricating oil before engine use.
• Radio Officer (R/O)
  An officer certified to operate GMDSS equipment and manage all radio communications on board; a role increasingly merged with other duties.
• Recommended Track
  A route of undefined width for the convenience of vessels in transit, indicated on charts but not mandatory.
• Reefer
  A refrigerated container or cargo space maintaining a controlled temperature for perishable goods during transport.
• Reefer Container
  A refrigerated ISO container with an integral refrigeration unit maintaining controlled temperatures for perishable cargo.
• Reefer Plug
  An electrical socket in a ship's hold or on deck providing power to a reefer container's refrigeration unit.
• Renewal Survey
  A statutory survey conducted to renew a SOLAS or MARPOL certificate for a further period, typically five years.
• Rhumb Line
  A course that crosses all meridians at the same angle, appearing as a straight line on a Mercator chart.
• RightShip
  A third-party maritime risk-assessment platform providing GHG ratings and vetting inspections used by cargo owners to screen vessels.
• Ro-Ro Vessel
  A ship with built-in ramps allowing wheeled cargo such as cars, trucks, and trailers to be driven directly on and off.
• Roll-On/Roll-Off (RoRo)
  Cargo handling method where wheeled vehicles or trailers drive on and off the vessel under their own power via ramps.
• Rotterdam Rules
  The 2008 UN convention on contracts for international carriage of goods wholly or partly by sea, modernising earlier cargo liability regimes.
• Running Fix
  A position obtained from two or more bearings of the same object taken at different times and advanced along the course line.
• Safe Working Load (SWL)
  The maximum load that lifting gear, mooring lines, or deck equipment is certified to bear without risk of failure in normal use.
• Safety Management Certificate (SMC)
  A certificate issued to a ship confirming its Safety Management System is operating in accordance with the ISM Code.
• SafetyNET
  The Inmarsat-C broadcast service transmitting maritime safety information including navigational warnings and weather forecasts in GMDSS Areas A3/A4.
• Scavenge Air
  Pressurised air supplied to the cylinder of a two-stroke diesel engine to expel exhaust gases and supply fresh charge for combustion.
• Sea State
  A description of wave conditions at a given location, typically expressed by significant wave height and period.
• Search and Rescue Transponder (SART)
  A radar transponder that responds to X-band radar pulses to indicate the position of a survival craft to SAR aircraft and vessels.
• Second Engineer (2/E)
  The engineer officer second in command, directly overseeing day-to-day operation and maintenance of the main propulsion plant.
• Second Mate (2/O)
  A certificated deck officer responsible for navigation equipment, charts, publications, and often designated ship's safety officer.
• Segregation
  The physical separation of incompatible dangerous goods in stowage to prevent hazardous reactions if packaging fails.
• Self-Contained Breathing Apparatus (SCBA)
  A compressed-air breathing set worn by firefighting team members to allow entry into oxygen-deficient or toxic atmospheres.
• Sewage Treatment Plant (STP)
  A biological or chemical system treating shipboard sewage to standards permitting overboard discharge under MARPOL Annex IV.
• Sextant
  A precision optical instrument used to measure the angle between a celestial body and the horizon for position fixing.
• Shaft Alley
  The enclosed tunnel running through the stern of the ship enclosing the propeller shaft from the engine room to the stern tube.
• Ship Security Officer (SSO)
  The officer on board responsible for implementing and maintaining the Ship Security Plan and liaising with the CSO and port facility security.
• Ship-to-Ship Transfer (STS)
  The transfer of cargo between two vessels moored alongside each other at sea or in an anchorage.
• Ship's Cook
  A certificated crew member responsible for preparing all meals and maintaining hygiene standards in the ship's galley.
• Sight Reduction
  The mathematical process of converting a celestial observation into a position line using tables or a calculator.
• Slop Tank
  A dedicated tank on tankers used to collect cargo residues and tank washing water, allowing oil-water separation before discharge.
• SOLAS Chapter III
  The chapter of SOLAS covering life-saving appliance requirements including lifeboats, liferafts, immersion suits, and drills.
• SOLAS Chapter IX
  The chapter of SOLAS making the ISM Code mandatory for ships, requiring companies to hold a Document of Compliance.
• SOLAS Chapter V
  The chapter of SOLAS dealing with safety of navigation, requiring ECDIS, AIS, VDR, pilot ladders, and bridge watchkeeping standards.
• Special Survey
  A comprehensive five-yearly classification survey requiring drydocking and full structural inspection to renew class for a further five years.
• Spring Line
  A mooring line leading forward or aft at a shallow angle to prevent the ship from moving ahead or astern.
• Squall
  A sudden, brief and intense increase in wind speed often accompanied by rain or hail, posing an immediate hazard to vessels.
• Standards of Training, Certification and Watchkeeping (STCW)
  International convention setting minimum training, certification, and watchkeeping standards for merchant ship officers and crew.
• Starting Air Receiver
  A pressure vessel storing compressed air at 30 bar used to crank and start the main engine and diesel generators.
• Stern Tube
  The watertight bearing assembly through which the propeller shaft passes through the hull from the engine room to the propeller.
• Stowage Factor (SF)
  The volume in cubic metres or cubic feet that one metric tonne of a commodity occupies when stowed in a ship's hold.
• Stowage Plan
  A diagram showing the planned or actual position of all cargo units aboard a vessel for a given voyage.
• Summer Draft
  The maximum permissible draft when loading in a Summer load line zone, shown on the ship's side as the Summer load line mark.
• Supercargo
  A cargo owner's representative sailing aboard a vessel to oversee the handling and care of the cargo throughout the voyage.
• Swell
  Long-period regular waves that have travelled out of the generating area, independent of current local wind conditions.
• Tailshaft Survey
  A classification survey of the propeller shaft withdrawn from the stern tube to inspect for corrosion, cracking, and bearing wear.
• Tank Cleaning
  The process of removing cargo residues and gas from cargo tanks using water, chemicals, or crude oil washing prior to loading a new cargo.
• Technical Superintendent
  A shore-side engineer responsible for overseeing planned maintenance, drydockings, and technical compliance of assigned vessels.
• Territorial Waters
  The belt of coastal waters extending up to 12 nautical miles from the baseline over which a coastal state has full sovereignty.
• Third Engineer (3/E)
  A junior engineer officer responsible for a watchkeeping duties and maintenance of assigned machinery and systems.
• Third Mate (3/O)
  The most junior certificated deck officer, typically responsible for maintaining fire-fighting and life-saving appliances.
• Three-Point Bearing
  A position fix obtained by simultaneously measuring horizontal angles between three charted objects using a sextant or compass.
• Tokyo Memorandum of Understanding (Tokyo MOU)
  A regional port state control arrangement covering the Asia-Pacific region, established in 1993 with 21 member authorities.
• Tonnage Certificate
  A statutory certificate stating a ship's gross and net tonnage calculated under the International Tonnage Convention 1969.
• Tonnes Per Centimetre (TPC)
  The mass required to change a vessel's mean draft by one centimetre, used to calculate draft changes during loading or discharging.
• Traffic Separation Scheme (TSS)
  An IMO-adopted routing measure separating opposing traffic into lanes to reduce collision risk in congested waters.
• Transit
  Two or more objects in line with each other, used as a position line or to verify vessel alignment in a channel.
• Trim
  The difference between forward and aft draft; a vessel trims by the head if forward draft exceeds aft draft.
• Trim by the Head
  A trim condition where the forward draft exceeds the aft draft, reducing steering effectiveness and increasing wave-making resistance.
• Trim by the Stern
  A trim condition where the aft draft exceeds the forward draft, generally preferred for sea passage to improve propulsive efficiency.
• True Bearing
  A bearing measured clockwise from true north, used for chart plotting and unaffected by magnetic variation or compass deviation.
• Turbocharger (TC)
  A device driven by exhaust gas that compresses intake air to increase diesel engine power output and fuel efficiency.
• Turbocharger Surge
  An abnormal flow reversal in a turbocharger compressor, evidenced by a loud banging or barking noise, caused by sudden load changes.
• Turnbuckle
  A threaded tensioning device fitted in a lashing rod or wire to adjust and tighten cargo securing arrangements.
• Turning Gear
  An electric motor-driven gear unit that slowly rotates the main engine crankshaft for maintenance, cooling-down, or warming-through.
• Twenty-foot Equivalent Unit (TEU)
  Standard unit of cargo capacity equivalent to one 20-foot ISO shipping container, used to measure container ship capacity.
• Twistlock
  A securing device that fits into container corner castings and locks by a 90° twist to stack and secure containers.
• Two-Stroke Engine
  A type of internal combustion engine completing the power cycle in a single up-and-down piston stroke, common in large slow-speed marine main engines.
• Typhoon
  A tropical cyclone of the western North Pacific with sustained winds exceeding 64 knots, the regional name for a hurricane.
• Unattended Machinery Space (UMS)
  A classification notation permitting the engine room to operate without a watchkeeper at night, subject to enhanced alarms and automation.
• United Nations Convention on the Law of the Sea (UNCLOS)
  The international treaty defining rights and responsibilities of nations in their use of the world's oceans, including maritime zones.
• Variation
  The angular difference between true north and magnetic north at a given location, shown on navigational charts.
• Very High Frequency Radio (VHF)
  Marine radio operating in the 156–174 MHz band used for short-range ship-to-ship and ship-to-shore communications.
• Very Large Crude Carrier (VLCC)
  A crude oil tanker with a deadweight of 200,000 to 320,000 DWT, among the largest vessels operating at sea.
• Very Low Sulfur Fuel Oil (VLSFO)
  Fuel oil with a sulfur content of 0.50% m/m or less, required globally under IMO 2020 sulfur cap regulations.
• Vessel Traffic Service (VTS)
  A shore-based radar and communications service that monitors and manages vessel movements in a port or busy waterway.
• VHF Channel 16 (Ch 16)
  The international distress, safety, and calling frequency at 156.8 MHz; all SOLAS ships must maintain a continuous watch on this channel.
• Voyage Data Recorder (VDR)
  A tamper-proof device recording bridge audio, radar images, and navigational data onto a protected capsule for post-incident investigation.
• Weather Routing
  A service providing vessel operators with recommended routes based on forecast weather and sea conditions to optimise safety and economy.
• Windlass
  A powered deck machine used to heave in or pay out anchor chain and sometimes mooring lines.
• Wiper
  The most junior engine room rating who cleans machinery spaces and assists with basic maintenance tasks.