M

The spaces containing the propulsion machinery, boilers, generators, and major auxiliaries; as high fire-risk areas they are subject to extensive fire-protection, escape, and safety requirements under SOLAS. IMO-grounded

A proprietary name for magnetic-particle inspection, a method of detecting surface and near-surface cracks in steel.

A compass that indicates direction by aligning with the earth's magnetic field; required to be carried as an independent heading reference under SOLAS, with corrections for the ship's own magnetism. IMO-grounded

A non-destructive test for surface and near-surface cracks in ferromagnetic materials, in which magnetic particles gather at flaws revealed by a magnetic field.

A ship's first voyage in service after delivery.

The system that stores, cools, filters, and circulates lubricating oil to the main engine's bearings, pistons, and other parts.

The space and equipment providing the ship's main electrical power, supplying the switchboard from which the ship's services are fed.

The power delivered by the main engines to drive the ship, the basis of its design speed.

The generating plant that normally supplies the ship's electrical needs, backed up by an independent emergency source as required by SOLAS. IMO-grounded

The divisions, not normally exceeding a set length, into which a passenger ship's hull and superstructure are subdivided by fire-resisting bulkheads to contain fire, as required by SOLAS chapter II-2. IMO-grounded

The ease with which equipment can be maintained and repaired, an important design consideration affecting availability and cost.

The work of keeping a ship and its equipment in proper condition, whether by routine servicing, planned overhaul, or repair.

The expenditure on keeping a ship and its systems in working order, a significant part of operating costs.

The continued compliance of a ship with classification rules, demonstrated through the programme of periodic surveys, on which the validity of its class depends. IMO-grounded

The tools and equipment carried aboard for the upkeep and repair of the ship's machinery and structure.

The tasks carried out to maintain the ship, ranging from routine servicing to repair, planned to minimise disruption to operation.

A serious failure category used in assessing tanker safety and risk, involving significant loss of containment or structural integrity.

A standard ship-handling manoeuvre to return a vessel to a person who has fallen overboard, the Williamson turn bringing the ship back along its original track.

A type of shackle used in mooring or rigging connections.

A small access opening, with a removable cover, allowing entry into a tank or enclosed space for inspection and maintenance.

A junction of pipes through which flows are distributed or collected, such as a tanker's cargo manifold.

A remotely controlled arm, for example on a remotely operated vehicle, used to handle tools and objects underwater.

An offshore installation or unit that is permanently or regularly staffed, as opposed to a normally unattended one.

The provision of crew to operate a ship; ships must carry a safe minimum manning appropriate to their type and operation, documented under SOLAS. IMO-grounded

A ship's ability to change and hold its course and speed in response to its rudder and engine, assessed against the IMO standards for manoeuvrability. IMO-grounded

A booklet aboard giving detailed information on the ship's manoeuvring characteristics, recommended by IMO to assist the master in ship handling. IMO-grounded

The measurable qualities describing how a ship responds in manoeuvres, such as turning circle, stopping distance, and course-keeping, evaluated under the IMO manoeuvring standards. IMO-grounded

The standards set by the IMO defining acceptable manoeuvring performance for ships, covering turning, initial turning, yaw-checking, and stopping ability. IMO-grounded

Information on a ship's handling characteristics, presented in a pilot card, wheelhouse poster, and manoeuvring booklet as recommended by the IMO. IMO-grounded

A reduced, controllable speed suitable for close-quarters manoeuvring and for prompt engine response.

The positions, such as the bridge, engine controls, and mooring stations, that are manned during manoeuvring into and out of port.

The standard trials, such as turning circles and zig-zag tests, carried out to measure a ship's manoeuvring characteristics against the IMO criteria. IMO-grounded

A mooring winch whose tension is adjusted by hand by the crew, as opposed to an automatic self-tensioning winch.

A line at least 76 millimetres below the upper surface of the bulkhead deck at the side, used in subdivision and damage-stability assessment as a limit the waterline must not reach after flooding. IMO-grounded

The plate forming the outboard edge of the inner bottom, connecting it to the bilge, bounding the double-bottom tanks.

The Maritime Research Institute Netherlands, a leading hydrodynamic research and model-testing organisation.

A proprietary marine evacuation system using a chute and inflatable platform to evacuate people from a ship into liferafts.

Systems, such as chutes or slides leading to inflatable platforms and liferafts, that allow rapid evacuation of large numbers of people from a ship; required and regulated under SOLAS and the LSA Code. IMO-grounded

The oils supplied for burning in ships' engines and boilers, ranging from heavy residual fuels to distillates, with quality and sulphur content regulated under MARPOL Annex VI. IMO-grounded

The large-diameter pipe connecting a floating drilling or production unit to equipment on the seabed, through which fluids and tools pass.

Organisations serving the maritime industry, such as trade associations, classification societies, and research institutes.

An official investigation into a marine casualty or incident to establish its causes and improve safety, conducted under the principles of the Casualty Investigation Code. IMO-grounded

The senior technical committee of the IMO, responsible for measures concerning the safety and security of shipping, which adopts and amends conventions such as SOLAS. IMO-grounded

Navigational and meteorological warnings, forecasts, and other urgent safety messages broadcast to ships, for example through NAVTEX and SafetyNET within the GMDSS. IMO-grounded

A membrane-type LNG cargo containment system (Mark III), in which the cargo is held by a corrugated stainless-steel membrane over insulation supported by the hull.

The International Convention for the Prevention of Pollution from Ships, the principal IMO treaty for preventing pollution of the sea and air by ships, comprising annexes covering different pollutant types. IMO-grounded

The MARPOL annex governing the control of pollution by noxious liquid substances carried in bulk, such as chemicals, including discharge criteria and tank-cleaning requirements. IMO-grounded

The MARPOL annex governing the prevention of pollution by harmful substances carried by sea in packaged form, linked to the IMDG Code. IMO-grounded

The MARPOL annex governing the prevention of pollution by sewage from ships, including treatment and discharge requirements. IMO-grounded

The MARPOL annex governing the prevention of pollution by garbage from ships, prohibiting or restricting the discharge of most wastes into the sea. IMO-grounded

The MARPOL annex governing the prevention of air pollution from ships, limiting emissions of sulphur and nitrogen oxides and addressing ship energy efficiency and greenhouse gases. IMO-grounded

Maritime security; the term is associated with maritime security levels used under the ISPS Code framework. IMO-grounded

The maximum allowable relief valve setting of a gas-carrier cargo tank, a key design pressure parameter under the IGC Code. IMO-grounded

An outbreak of illness affecting many persons aboard, requiring a public-health response.

A vertical structure carrying lights, antennas, signalling gear, and sometimes cargo-handling equipment.

The control device by which an operator sets the demand to a system, such as a propulsion or winch control.

The greatest speed the ship is designed to maintain ahead in service at its deepest draught, a reference for navigation and manoeuvring equipment. IMO-grounded

The highest pressure at which a piping system may safely be operated, used as a design and safety limit.

The greatest speed the ship can attain going astern, relevant to manoeuvring and stopping.

The maximum power and speed at which an engine is designed to run continuously, the basis for its rating.

The internationally recognised spoken distress signal, indicating grave and imminent danger and a request for immediate assistance. IMO-grounded

A unit denoting a thousand cubic feet, used for volumes of natural gas.

A statistical measure of the average operating time between failures of equipment, used to express reliability.

The arrangements provided to recover persons from the water and from survival craft, required under SOLAS, distinct from the means of evacuation. IMO-grounded

The ratio of an engine's output power to the power developed in its cylinders, accounting for friction and other mechanical losses.

A shaft seal using precisely finished mating faces, one rotating and one fixed, to prevent leakage along a rotating shaft, used in pumps.

Fire-fighting foam of intermediate expansion ratio between low- and high-expansion foam.

A diesel engine running at moderate speed, more compact than a low-speed engine and usually driving the propeller through gearing or generators.

An engine, typically four-stroke, running at moderate rotational speed, widely used for propulsion through gearing and for power generation.

The change of a solid to liquid on heating to its melting point.

A sewage-treatment technology combining biological treatment with membrane filtration to produce a high-quality effluent, used in advanced shipboard sewage plants under MARPOL Annex IV. IMO-grounded

A gas-carrier cargo tank in which a thin metal membrane forms the liquid barrier, the loads being transmitted through insulation to the hull, as in the Mark III and No96 systems under the IGC Code. IMO-grounded

The use of selectively permeable membranes for separation, such as in reverse-osmosis fresh-water generators and advanced sewage treatment.

An LNG containment system using a thin membrane backed by insulation supported by the inner hull, allowing the cargo loads to be carried by the ship's structure; built to the IGC Code. IMO-grounded

A regional agreement among maritime authorities to coordinate the inspection of foreign ships in their ports, to verify compliance with international standards and detain substandard ships. IMO-grounded

A proprietary podded electric propulsion unit providing combined propulsion and steering.

A light line used to haul across a heavier rope or hawser during mooring or transfer operations.

The space where the crew take their meals.

The point about which a ship is considered to oscillate for small angles of heel, the intersection of successive lines of buoyant force; its height above the centre of gravity determines initial stability. IMO-grounded

The vertical distance between the centre of gravity and the metacentre (GM), the principal measure of a ship's initial stability; minimum values are set by intact-stability criteria. IMO-grounded

An ice-like solid in which methane is trapped within a water lattice, found in seabed deposits and of interest as a potential energy source.

A flow-improving duct fitted ahead of the propeller to condition the inflow and improve propulsive efficiency.

Intermediate, often movable, decks fitted between main decks to increase the area for vehicles or cargo.

A geometric property of the hull's midship cross-section relating bending moment to stress, central to assessing the longitudinal strength of the hull girder.

The layer of iron oxide formed on steel during hot rolling, which must be removed before coating because it is loose and promotes corrosion.

A valve-timing technique in which the inlet valve is closed early or late to modify the effective compression, used to improve efficiency and reduce nitrogen-oxide formation.

A schematic display of a system showing its components and their status, helping operators monitor and control it.

The rated breaking strength of a mooring line, the basis for selecting lines and for the design of mooring fittings and winches.

The least standard of accommodation conditions, such as temperature, ventilation, and noise, considered acceptable for the crew's comfort, addressed under the Maritime Labour Convention. IMO-grounded

A less serious failure category used in assessing tanker safety and risk, involving limited loss of containment or function.

A condition in which components that should be in line, such as shafting and bearings, are out of alignment, causing extra stress, wear, and vibration.

A general category for items not falling under other specific headings.

A proprietary fin arrangement fitted ahead of the propeller to recover swirl energy and improve propulsive efficiency.

The stowage together of different cargoes, which must observe segregation rules where dangerous goods are involved. IMO-grounded

One million British thermal units, a unit of energy used in the gas trade, for example for pricing LNG.

Million standard cubic feet per day, a unit of gas flow rate used in the gas industry.

Equipment provided to recover a person who has fallen overboard from the water back to the ship, part of the means of rescue. IMO-grounded

A proprietary mobile or floating docking system.

Movable offshore structures such as drilling rigs and accommodation units that can be relocated; mobile offshore drilling units are addressed by the IMO MODU Code. IMO-grounded

Test facilities (towing tanks and basins) in which scale ship models are tested to measure resistance, propulsion, seakeeping, and manoeuvring.

A cargo space atmosphere with altered gas composition, for example reduced oxygen, used to preserve perishable cargo.

The turning effect of a force about a point, equal to the force times its distance, fundamental to stability and structural analysis.

A measure of a body's resistance to angular acceleration about an axis; the area moment of inertia of a section measures its resistance to bending.

The righting moment that tends to return a heeled ship to upright, equal to the displacement times the righting arm. IMO-grounded

The continuous observation and measurement of conditions or parameters to detect changes and ensure safe operation.

A system that measures and displays the state of machinery and ship functions and raises alarms on abnormal conditions.

A bridge or control-room position from which the ship's systems are monitored.

A small crane running on an overhead rail used to handle stores and provisions.

The international agreement to phase out substances that deplete the ozone layer, such as halons and CFCs, which has driven the replacement of these fire-extinguishing agents and refrigerants aboard ship. IMO-grounded

An opening through the hull of an offshore or specialised vessel through which equipment, divers, or tools are deployed into the sea while sheltered from waves.

The securing of a ship to a berth, buoy, or another vessel using lines and ground tackle.

A manual recommended by the IMO giving information on the ship's mooring and towing arrangements and their safe use. IMO-grounded

The plan of lines and fittings used to hold a ship at a berth, arranged to restrain it against wind, current, and tide.

The drums of a mooring winch on which the mooring lines are wound.

The winches, drums, capstans, bitts, fairleads, and lines used to moor a ship; shipboard fittings and supporting structure are subject to strength requirements. IMO-grounded

The deck fittings such as bollards, bitts, fairleads, and chocks used in mooring and towing, whose strength and arrangement are governed by class and IMO requirements. IMO-grounded

The ropes or wires used to secure a ship to a berth or buoy.

The restraining force that the mooring arrangement provides to hold the ship against environmental forces.

The ability of the mooring system to keep the ship safely secured under the expected loads.

The complete arrangement of lines, fittings, and equipment by which a ship or floating unit is held in position, which for offshore units may include anchors and chains.

Tests of the mooring winches and arrangements to confirm they perform as required.

A powered winch used to heave in and hold mooring lines, often with an automatic tensioning capability.

The brake on a mooring winch drum that holds the line under load and renders (slips) at a set tension to protect the line and fittings.

The load the mooring-winch brake is designed to hold, set in relation to the line's breaking load to ensure the line renders before it parts.

The powered winches used for handling and holding mooring lines aboard ship.

The power systems (electric, hydraulic, or steam) that drive mooring winches.

A self-supporting spherical-tank LNG containment system (Moss type) in which independent spherical tanks carry the cargo, built to the IGC Code. IMO-grounded

The protective housings of electric motors, classified by their degree of protection against ingress and, for hazardous areas, by their type of explosion protection.

The device used to start and stop an electric motor and protect it from overload.

The vertical distance from the top of the keel to the underside of the freeboard deck at side, measured to the moulded lines, a principal dimension.

The draught measured to the moulded baseline (top of keel) rather than to the bottom of the keel.

The lines defining the hull form to the inside of the shell plating, the reference surface for the ship's dimensions and structure.

A perforated box fitted on the end of a bilge suction pipe that strains out debris to prevent it blocking the pump.

An offshore mooring arrangement in which a tanker is held by several buoys and its own anchors while connected to a pipeline for loading or discharging.

A ship designed to carry several different cargo types, such as general cargo, containers, and bulk, with flexible holds and cargo gear.

A versatile dry-cargo ship able to carry a range of cargoes including break-bulk, containers, and project cargo.

Offshore vessels equipped to carry out a variety of subsea tasks, such as construction, inspection, and intervention, often with cranes and remotely operated vehicles.

The handling of more than one container in a single lift, using a spreader designed to grip several boxes at once.

A mushroom-shaped fitting, such as a mushroom ventilator head or a mushroom anchor used for permanent moorings.

A type of watertight or weathertight door arrangement.