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Encyclopedia of Marine Technology


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National authorities

Either the government of the country in which the ship is registered, or the Administration delegated to deal with merchant shipping for that country.

Natural gas (dry)

Gas without condensation at common operating pressures and temperatures where the predominant component is methane with some ethane and small amounts of heavier hydrocarbons.

Natural gas fuel

With new emission control regulations taking effect, gas as a ship fuel, once banned, is now re-emerging as an environmentally and economically attractive option.

Natural gas-fuelled ferry GLUTRA

Financed by the Norwegian Directorate of Public Roads, a car ferry GLUTRA with a capacity of 100 private cars was designed for operation on natural gas, based on a new set of Norwegian safety standards for gas fuelled passenger ships.

Natural gas-fuelled ferry VIKING GRACE

The PaxCar ferry VIKING GRACE is the largest LNG fuelled passenger ship. Built in STX Turku yard, the ship is designed for efficient year-round service on the trans-Baltic route linking the southwest Finnish port of Turku with Stockholm.

Nautical chart

A map of water area including the adjoining land, intended primarily for use of mariners.

Nautical mile

Distance of one minute of longitude at the equator, equal to 1852m.

Naval architecture

The science and practice of designing ships as distinguished from their construction which is covered to shipbuilding.

Navigating and manoeuvring workstation

The main workstation on the bridge where speed and course are considered and controlled, preferably conceived for working in the seated position with optimum visibility and integrated presentation of information and operating equipment.


All tasks relevant for deciding, executing and maintaining the course and speed in relation to waters and traffic.

Navigation aids

Magnetic compass, gyrocompass, radar, echo sounder, rudder angle indicator, propeller revolution counter, rate of turn indicator.

Navigation aids vessel

A vessel intended for buoy handling.

Navigation lights

All seagoing ships must be equipped with running and signal lights in compliance with the International Regulations for Preventing Collision at Sea (COLREG).


The person navigating, operating the bridge equipment and manoeuvring the ship.


An international maritime radio telex system sponsored by IMO and IHO, which automatically receives the broadcast telex information such as navigational, meteorological warnings and search and rescue (SAR) alerts on 24-hour watch basis.

Necking effect

A term describing local corrosion at junction of plating and stiffeners due to flexure effects caused by reverse, cycling loading with loss of coating or shedding of scale exposing fresh steel to further corrosion.

Net cutters

Stainless steel net cutters are mounted on the rope guard, overlapping the propeller hub.

Net pick-up

A net protection ring with U-shaped cross-section. The net pick-up is the ancillary component of the sterntube aft seal and its purpose is to prevent netting and fishing lines from entering the seal.

Nitrile rubber

A synthetic rubber that is a copolymer of butadiene and acrylonitrile. It has good resistance to petroleum-based substances and is often used in seals.

Nitrogen generator

Chemical tankers, gas carriers and reefer ships need clean, dry nitrogen for inerting, purging and cargo padding.

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