Extended Operational and Trade Vocabulary

Nautical Science, Navigation and COLREGs glossary (page 2)

The formal navigation and collision-avoidance vocabulary: position accuracy and fix terminology, ARPA target acquisition, abnormal refraction, celestial and terrestrial methods, and the COLREGs rules of the road. Grounds each term in the navigational practice and the collision regulation it serves, the precise counterpart to the deck-seamanship section.

734 defined terms.

Showing 250 on this page (page 2 of 3).

G

Ground wave: Radio wave propagating along the Earth's surface.
GTS (Global Telecommunications System): WMO system for exchange of meteorological data.
Gulf Stream: Warm western boundary current of the North Atlantic.
Gyro error: Difference between true north and gyro north, expressed as east or west.
Gyro repeater: Compass card driven by a gyrocompass at a remote location.
Gyrocompass: Heading reference required by SOLAS Chapter V.

H

Hadley Cell: Tropical atmospheric overturning circulation between the equator and around 30 degrees latitude.
Half convergency: Half the difference in longitude between two points, used in radio bearings.
Halo (optical): Ring around the Sun or Moon caused by ice crystals.
Harmonic constants: Amplitudes and phases of tidal constituents at a port.
Harmonic prediction: Method of predicting tides using harmonic constituents.
HAT (Highest Astronomical Tide): Highest tidal level predicted under average meteorological conditions.
Haze: Suspension of dry particles reducing visibility to between 1 and 5 km.
Head-up display: Radar/ECDIS orientation with ship's head at the top.
Heading: Direction in which a vessel's bow is pointing.
Heading line: Radar bearing line indicating own ship's heading.
Heading marker: Index on a compass card aligned with the lubber line.
Heave: Vertical translational motion.
Helmsman: Person at the wheel.
Hertz (Hz): Unit of frequency.
High pressure: Region of pressure higher than its surroundings; anticyclone.
High water (HW): Maximum height reached by a rising tide.
HO-211: Ageton's tables for sight reduction; older US Navy publication.
HO-229 (NGA Pub 229): Sight Reduction Tables for Marine Navigation, six volumes.
HO-249 (NGA Pub 249): Sight Reduction Tables for Air Navigation, three volumes, used at sea for stars.
Horizon: Apparent line where Earth and sky meet; visible, sensible or celestial.
Horizontal angle: Angle between two terrestrial objects in the horizontal plane.
Horizontal sextant angle (HSA): Position-fixing technique using two horizontal angles.
Hour angle: Angular distance west of meridian.
Hour circle: Great circle through a celestial body and the celestial poles.
Humidity: Water-vapor content of the atmosphere.
Hurricane: Tropical revolving storm with winds 64 knots or above in the North Atlantic and eastern North Pacific.
Hydrographic Office: National hydrographic agency producing charts.
Hydrography: Science of surveying water bodies.

I

IALA: International Association of Marine Aids to Navigation and Lighthouse Authorities.
IBC Code: International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk.
Iceberg: Mass of ice broken from a glacier and floating in the sea.
IHO (International Hydrographic Organization): Intergovernmental body governing hydrographic standards.
IMO (International Maritime Organization): UN agency responsible for SOLAS, COLREGs, MARPOL and related instruments.
IMRay chart: Leisure chart series published by Imray, Laurie, Norie and Wilson.
Index correction (IC): Error of the sextant determined by the index error test.
Index error: Sextant error when the true reading should be zero.
Inferior planet: Planet whose orbit lies inside Earth's, Mercury or Venus.
Inmarsat: Satellite communications provider for GMDSS and commercial services.
Inmarsat C: Polling/EGC/SafetyNET service in GMDSS.
Inmarsat Fleet: Voice/data service (legacy).
Inmarsat FleetBroadband: Higher-bandwidth IP service.
Inshore traffic zone (ITZ): Area between landward boundary of a TSS and the coast, governed by COLREGs Rule 10(d).
Inspection (chart): Visual check of a chart before use.
INT chart: International chart conforming to IHO specifications.
Intercept (Marcq Saint-Hilaire): Difference between calculated and observed altitudes, plotted along the azimuth.
Interfix gap: Time interval between successive fixes.
International Code of Signals: Referenced under SOLAS V/21.
International date line: Approximately the 180-degree meridian where the date changes.
Intertropical Convergence Zone (ITCZ): Belt of low pressure near the equator where trade winds converge.
Inverter (electrical): DC-to-AC converter; common bridge equipment item.
Isallobar: Line of equal pressure change.
Isobar: Line of equal atmospheric pressure on synoptic chart.
Isogonal (isogonic line): Line of equal magnetic variation.
Isogriv: Line of equal grid variation.
Isohel: Line of equal sunshine duration.
Isotherm: Line of constant temperature.

J

Jet Stream: Narrow band of strong upper-tropospheric winds.
Jettison position: Logged position at which cargo or stores are jettisoned.
JRCC (Joint Rescue Coordination Center): Combined maritime and aeronautical RCC.

K

K1: Lunar-solar declinational diurnal tidal constituent with period 23.93 hours.
Katabatic wind: Downslope wind driven by cool dense air.
Kelvin scale: Absolute temperature scale used in meteorology.
Knot: One nautical mile per hour.
Kuroshio: Major warm western boundary current of the North Pacific.

L

Lambert conformal projection: Conic projection used for aeronautical and some nautical charts.
Land breeze: Offshore wind at night caused by cooling land.
LAT (Lowest Astronomical Tide): Modern chart datum.
Latitude: Angular distance north or south of the equator.
Lay of the land: Coastal topography as seen from seaward.
Lead Line: Traditional weighted line for taking soundings.
Leading line: Line passing through two leading marks indicating a safe approach.
Leeway: Lateral drift of a vessel caused by wind.
LHA (Local Hour Angle): GHA combined with longitude (east added, west subtracted).
Light characteristic: Color, period, sequence and identification of a navigation light.
Light list: Publication listing aids to navigation; ALL or USCG Light List.
Light sector: Arc through which a sectored light shows a particular color.
Lighthouse: Tower with a navigational light.
Limiting danger line: Line on a chart beyond which dangers exist.
Line of position (LOP): Line on which an observer's position is known to lie.
Local apparent noon (LAN): Instant when the Sun is on the observer's meridian.
Local mean time (LMT): Mean time at the observer's meridian.
Log (ship's): Record of navigational events; or instrument for measuring speed/distance.
Longitude: Angular distance east or west of the prime meridian.
Look-ahead sector (ECDIS): ECDIS-defined sector ahead of own ship monitored against safety alarms.
Lookout: Person stationed to watch for objects ahead.
Loran-C: Legacy hyperbolic radionavigation system.
Low water (LW): Lowest level reached by a falling tide.
Lower limb: Lower edge of the Sun or Moon's disc as observed in a sextant.
Lubber line: Reference line on compass aligned with ship's head.
Lunar distance: Angle between the Moon and another body, historic time-determination method.
Lunitidal interval: Time between the Moon's transit and the following high water.

M

M2: Principal lunar semi-diurnal tidal constituent with period 12.42 hours.
Magnetic anomaly: Localized departure from expected magnetic variation.
Magnetic compass: Standard magnetic compass per ISO 449.
Magnetic course: Course referred to magnetic north.
Magnetic equator: Line on Earth where magnetic dip is zero.
Magnetic meridian: Line on Earth in the direction of the horizontal magnetic field.
Magnetic north: Direction toward magnetic north pole.
Magnetic variation: Angle between true and magnetic north at a location.
Marine forecast: Weather forecast for coastal and offshore waters.
Marine Safety Information (MSI): NAVAREA warnings, weather and other safety broadcasts.
Mariner's Handbook (NP100): UKHO general reference for navigation and bridge practice.
Maritime mobile service identity (MMSI): Nine-digit unique identifier for DSC and AIS.
Master's standing orders: Written instructions to OOW.
Mean High Water (MHW): Average of all high waters over a tidal datum epoch.
Mean High Water Springs (MHWS): Average level of all high waters at spring tides.
Mean Low Water (MLW): Average of all low waters over a tidal datum epoch.
Mean Low Water Springs (MLWS): Average level of all low waters at spring tides.
Mean sea level (MSL): Average level of the sea surface.
Mean solar time: Time based on a fictitious mean Sun moving uniformly.
Mercator projection: Conformal chart projection with rhumb lines as straight.
Mercurial barometer: Barometer using a column of mercury.
Meridian: Great circle through both geographic poles.
Meridian altitude: Altitude of body on observer's meridian.
Meridian passage: Instant when a body crosses the observer's meridian.
Meteorological tide: Departure of actual tide from predicted due to weather effects.
MF/HF radio: Medium and high-frequency radio used in GMDSS Sea Areas A2 and A3.
Micrometer drum: Sextant drum reading minutes of arc.
Mid-latitude sailing: Plane-sailing method using mid-latitude for departure conversion.
Millibar (mb): Unit of atmospheric pressure equal to one hectopascal.
Mixed Tide: Tide with significant diurnal and semidiurnal components.
Mob (Man Overboard): MOB drill/COB procedure.
Mode A/C/S (transponder): Aircraft-related (not maritime).
Monsoon: Seasonally reversing wind system bringing strong climatic forcing, especially in the Indian Ocean.
Moonrise / Moonset: Times when the Moon rises or sets.
Most probable position (MPP): Best estimate of position given available information.
MSI (Maritime Safety Information): Broadcast warnings, weather and SAR information per GMDSS.

N

Napier diagram: Graphical plot of compass deviation against heading.
Nautical Almanac: Annual joint UK/US publication.
Nautical mile: 1852 m international nautical mile.
Nautical twilight: Period when the Sun is between 6 and 12 degrees below the horizon; used for star sights.
NAVAREA: One of 21 navigational warning areas under the Worldwide Navigational Warning Service relevant to incident broadcasts.
NAVAREA warning: Long-range navigational warning issued by an area coordinator.
Navigable semicircle: Side of a TRS away from the storm track, less hazardous.
Navigation alarms (ECDIS): Alerts for crossing safety contour, area warnings, off-track and others.
Navigational warning: Notice broadcast to mariners about hazards to navigation.
Navigator: Officer responsible for the safe navigation of the vessel.
NAVTEX: GMDSS broadcast service under SOLAS IV.
Neap Tide: Tide with smallest range, near first and third lunar quarters.
Night order book: Record of master's specific orders for the night.
NIPC (Notices to Mariners Permanent Index of Corrections): Cumulative list of in-force chart corrections.
No-go area: Area on passage plan excluded from passage.
NOAA chart: US nautical chart issued by NOAA Office of Coast Survey.
Noon position: Daily fix near LAN reported to the company.
North-up display: Radar/ECDIS orientation with true north at the top.
NorthEastern Atlantic Pilot: One of UKHO's regional sailing-direction volumes.
Notice of Intent (sailing): Pre-arrival or pre-departure notice to authorities.
Notices to Mariners (NTM): Weekly amendments to charts and publications; UKHO Section II and US NGA NTM.
NP100: The Mariner's Handbook (UKHO).
NP131: Catalogue of Admiralty Charts and Publications.
NP136: Ocean Passages for the World (UKHO).
NP201 to NP204: Admiralty Tide Tables, by world region.
NP203: Admiralty Tide Tables Volume 3, Indian Ocean and South China Sea.
NP218 series: Tidal Stream Atlases (multiple volumes).
NP281: Admiralty List of Radio Signals Volume 1, Coast Radio Stations.
NP282: ALRS Volume 2, Radio Aids to Navigation, Differential GPS, AIS.
NP283: ALRS Volume 3, Maritime Safety Information Services.
NP284: ALRS Volume 4, Meteorological Observation Stations.
NP285: ALRS Volume 5, GMDSS.
NP286: ALRS Volume 6, Pilot Services, VTS and Port Operations.
NP303: Sight Reduction Tables for Marine Navigation (UKHO; UK equivalent of HO-229).
NP314: The Nautical Almanac (UKHO joint with USNO).
NP5011: Symbols and Abbreviations used on Admiralty Charts.
NP735: IALA Maritime Buoyage System (UKHO).
Nuclear-powered vessel: Vessel governed by SOLAS Chapter VIII.

O

O1: Principal lunar diurnal tidal constituent, period 25.82 h.
Object glass: Front lens of a telescope or sextant.
Observed altitude (Ho): Sextant altitude corrected for index, refraction, dip.
Occluded front: Front formed when a cold front overtakes a warm front.
Occulting light: Light in which total duration of light exceeds darkness.
Ocean current: Persistent flow of ocean water.
Ocean Passages for the World (NP136): UKHO publication describing recommended ocean routes.
OOW (Officer of the Watch): Officer in charge of the navigational watch.
Open sea: Area of sea beyond inshore traffic zones and TSSs.
Optical range: Distance at which a light is theoretically visible by eye.
Original of bearing: Time and value of a bearing as first observed.
Orographic lifting: Rise of air over high ground producing cloud and rain.
Outline plan: Initial summary plan in passage planning appraisal.
Overcast: Sky cover of 8 oktas.
Overfalls: Steep choppy seas at tidal races marked on charts.

P

Pacific Pilot: UKHO Sailing Directions for the Pacific.
Parallax (celestial): Angular difference between observation from Earth's surface and Earth's center.
Parallel index (PI): Radar parallel-indexing technique.
Parallel of latitude: Small circle parallel to the equator.
Parallel ruler: Drafting instrument for transferring parallel lines on a chart.
Passage plan: Berth to berth voyage plan under SOLAS Chapter V.
Pelorus: Sighting device with compass rose for taking relative bearings.
Perigee: Point in the Moon's orbit nearest Earth.
Perihelion: Point in Earth's orbit nearest the Sun.
Pilot card: Standard A4 card given to pilot.
Pilot chart: Chart showing average meteorological and oceanographic data by month.
Pilot station: designated boarding area at sea.
Pilotage: Conduct of vessel by a licensed pilot.
Pitch (motion): Rotational motion about the transverse axis.
Plane sailing: Approximate method assuming a flat Earth over short distances.
Planning stage: Second stage of passage planning per A.893(21).
Plot: Graphical representation of vessel movement.
Plotting sheet: Sheet with latitude and longitude grid for plotting positions.
Point: Direction; 11.25 degrees on the compass.
Polar chart: Chart for use in polar regions, often gnomonic or stereographic.
Polar Code: Adopted under SOLAS XIV and MARPOL; complements Article 234 jurisdiction.
Polaris: Star Alpha Ursae Minoris; used for latitude north of about 1 degree N.
Polaris correction: Tabular correction (a0, a1, a2) applied to Ho of Polaris to obtain latitude.
Port: Left-hand side of a vessel when facing forward; also a harbor.
Position (DR): Position by dead reckoning.
Position (estimated): Position by DR adjusted for set and drift.
Position fixing: Determining the vessel's position.
Position line: Locus on which the vessel lies.
Pre-arrival information: PAI required by the FAL Convention.
Pressure gradient: Rate of change of pressure with distance.
Prevailing wind: Wind that blows most frequently from a particular direction.
Prime Meridian: Reference meridian for longitude, historically Greenwich.
Prime vertical: Great circle through the zenith and east and west points of the horizon.
PRINS (Pure Inertial Navigation System): Inertial navigation independent of GNSS.
Procedure (collision avoidance): Steps taken in compliance with COLREGs to avoid collision.
Promulgation (NTM): Issue and distribution of Notices to Mariners.
Protractor: Instrument for measuring angles on a chart.
PSC (Port State Control): Inspection of foreign ships in national ports.
Pub 102: NGA International Code of Signals.
Pub 117: NGA Radio Navigational Aids.
Pub 1310: NGA Radar Navigation and Maneuvering Board Manual.
Pub 150: NGA World Port Index.
Pub 151: NGA Distances Between Ports.
Pub 217: NGA Maneuvering Board Manual.
Pub 9: Bowditch, The American Practical Navigator.
PZX triangle: Astronomical triangle on the celestial sphere.

Q

QFE: Atmospheric pressure at field elevation (aviation).
QFF: Sea-level pressure used in synoptic meteorology.
QNH: Altimeter setting giving elevation above MSL (aviation).
Quadrantal correctors: Soft-iron spheres on magnetic compass binnacle.
Quartering sea: Sea on the quarter.

R

Racon: Radar transponder marking AtoNs.
Radar: Radio detection and ranging device required by SOLAS V/19.
Radar plotting: Manual or automatic determination of target motion and CPA.
Radar Reflector: Passive device enhancing radar return.
Radar shadow: Area shielded from radar by high ground or structures.
Radial dispersion: Spread of bearings about a mean.
Radio bearing: Bearing determined by direction-finding equipment.
Radio direction finder (RDF): Receiver with directional antenna for taking radio bearings.
Radio Regulations: ITU instrument governing radio use, including maritime bands.
Range light: Two fixed lights in line indicating channel.
Range of tide: Vertical difference between consecutive high and low waters.
Range, nominal: Maximum range of a light in 10 nm meteorological visibility.
Raster chart (RNC): Scanned image of a paper chart conforming to IHO S-61.