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The government bodies of a state responsible for maritime matters, such as the flag administration and port and coastal authorities, which implement and enforce international and national requirements. IMO-grounded

In a power converter, the turning-off of a switching device by the natural reversal of the supply, as opposed to forced commutation.

The frequency at which a structure or system tends to vibrate freely; matching it with an exciting frequency causes resonance, which must be avoided in shafting and structure.

Natural gas from which the heavier liquefiable hydrocarbons and water have been removed, leaving mainly methane.

Natural gas used as fuel for ship engines, offering lower emissions than oil fuels; its use is governed by the IGF Code under SOLAS. IMO-grounded

A map of a sea area showing depths, hazards, aids to navigation, and coastlines, used for safe navigation; carriage of up-to-date charts is required under SOLAS chapter V. IMO-grounded

A unit of distance used at sea, equal to 1,852 metres, approximately one minute of latitude.

The engineering discipline concerned with the design, construction, and behaviour of ships and floating structures, covering form, strength, stability, and propulsion.

The bridge position equipped with the controls and displays needed to navigate and manoeuvre the ship.

The art and science of safely directing a ship from one place to another, determining position, course, and speed.

External and shipborne devices that assist navigation, such as buoys, lights, radar, and electronic positioning systems.

A vessel used to service and maintain navigational marks such as buoys and beacons.

The lights a vessel must show at night and in restricted visibility to indicate its presence, type, and aspect, as prescribed by the collision regulations (COLREGs). IMO-grounded

The officer responsible for the ship's navigation, including passage planning and position fixing.

An automated international service that broadcasts navigational and meteorological warnings and other safety information to ships by direct-printing telegraphy, part of the GMDSS. IMO-grounded

The local reduction in cross-section of a ductile material under tension before it fractures, seen in tensile testing.

Cutting devices fitted to protect a vessel or its equipment from entanglement in nets, or used in fishing operations.

The hauling aboard of a fishing net and its catch.

A synthetic rubber resistant to oil and fuel, used for seals, gaskets, and hoses where oil resistance is needed.

Equipment that produces nitrogen from air, for example by membrane or pressure-swing adsorption, used to inert tanks and spaces aboard ship. IMO-grounded

Pollutant gases formed during high-temperature combustion in engines; their emission from ships is limited under MARPOL Annex VI and the NOx Technical Code. IMO-grounded

A nitrogen-oxygen compound that is a potent greenhouse gas, also produced in small amounts by combustion. IMO-grounded

A point of a vibrating system that remains stationary; also a connection point in a structure or network.

The IMO Code on Noise Levels on Board Ships, which sets limits on noise in various spaces to protect seafarers' health and provide acceptable working and living conditions. IMO-grounded

Material that neither burns nor gives off flammable vapours in sufficient quantity to ignite when heated, as defined and tested under SOLAS for fire-resisting construction. IMO-grounded

A grease using an inorganic thickener, such as clay, suited to high-temperature applications.

A valve that permits flow in one direction only and prevents reverse flow; see check valve.

A mooring winch with a single undivided drum, on which the full length of line is wound, as distinct from a split-drum winch.

A mooring-winch drum that is not divided into tension and storage parts, carrying the line in a single barrel.

Petroleum products with a high flashpoint that do not readily give off flammable vapour at normal temperatures, handled with fewer fire precautions than volatile products. IMO-grounded

Testing that examines material or welds for defects without damaging them, using methods such as radiography, ultrasonics, and dye penetrant.

The NDT techniques used to verify the soundness of hull welds, including visual, magnetic particle, dye penetrant, ultrasonic, and radiographic methods.

The condition in which the ship as a whole, its machinery, services, and means of habitability are functioning normally, a reference state in safety requirements. IMO-grounded

A heat treatment in which steel is heated and air-cooled to refine its grain and improve its mechanical properties and toughness.

The status of a vessel unable to manoeuvre as required by the collision regulations because of some exceptional circumstance, which must show the prescribed lights and shapes. IMO-grounded

A material's ability to resist brittle fracture in the presence of a notch or stress concentration, important for the safe behaviour of structural steel.

The release of nitrogen oxides in engine exhaust, limited for marine engines under MARPOL Annex VI according to engine speed. IMO-grounded

The IMO code, mandatory under MARPOL Annex VI, setting out how marine diesel engines are tested, surveyed, and certified for their nitrogen-oxide emissions. IMO-grounded

A synthetic polymer used for ropes, bearings, and components, valued for strength, elasticity, and wear resistance; nylon mooring lines absorb shock loads well.