Ship Science and Engineering

Nautical Science glossary

The discipline of navigating, handling, and watchkeeping: terrestrial, celestial, and GNSS-based navigation, collision avoidance under the COLREGs, ECDIS and ENCs migrating from S-57 to the IHO S-100 framework, radar and ARPA, AIS and integrated bridge systems, and voyage planning across appraisal, planning, execution, and monitoring. Includes ship handling (pivot point, squat, turning circle), meteorology, weather routing, and tidal prediction.

249 defined terms.

A

Abeam: Bearing 090° relative to ship's heading.
Adcock antenna (radio DF): Direction-finding antenna used in marine RDF.
Aero light: Aeronautical light reported on charts.
Aids to Navigation (AtoN): Buoys, beacons, lights, fog signals, racons.
AIS (Automatic Identification System): Class A/B transponder per ITU-R M.1371.
Almanac (Nautical): Annual ephemeris tables for celestial navigation.
ALRS: Admiralty List of Radio Signals (Vols 1-6).
Altitude (celestial): Angle between horizon and celestial body.
Anchor watch: Watch maintained on anchored vessel.
Angle of cut: Angle between two LOPs on a chart.
Anomalistic month: Time between successive perigees of the Moon.
Apparent wind: Wind perceived from a moving vessel.
ARPA (Automatic Radar Plotting Aid): Auto tracking and CPA/TCPA per IMO Res. A.823(19).
Aspect (target): Relative bearing of own vessel from target.
Assumed position (AP): Reference position for sight reduction.
Astronomical triangle: Celestial PZX triangle for sight reduction.
Atmospheric refraction: Bending of light reducing observed altitude.
Augmentation (Moon): Apparent increase in Moon's semi-diameter near zenith.
Aural sound signal: Whistle/horn signal per COLREGs Annex III.
Autonomous Surface Vessel (MASS): IMO-defined classification of autonomous ships.
Azimuth: Bearing of a celestial body measured from true north.

B

Beacon: Fixed AtoN, lit or unlit.
Beam sea: Seas approaching the vessel from abeam.
Bearing line of position: LOP from a single compass bearing.
Beaufort scale: Empirical wind force scale 0-12.
Berth-to-berth passage plan: SOLAS V/34 mandated passage plan.
Black-ball day shape: Anchor-day shape per COLREGs Rule 30.
Bow-and-beam bearings: Special-case running fix method.
Bridge Resource Management (BRM): STCW competence in bridge team performance.
Bridge Watchkeeping Standard (STCW A-VIII/2): Mandatory watchkeeping requirements.

C

Cardinal mark (IALA): Buoy indicating safe water on a cardinal quadrant.
Catalog of charts: NOAA/UKHO catalog listing chart numbers and coverage.
Celestial fix: Position from intercept of two or more celestial LOPs.
Celestial sphere: Imaginary sphere with stars projected onto it.
CES (Coastal Earth Station): GMDSS Inmarsat shore station.
Chart datum (CD): Reference for sounding depths, usually LAT.
Chart No. 1: NOAA/UKHO chart symbol legend.
Check-off list (ECDIS): ECDIS route safety check sequence.
CIRM: Comite International Radio-Maritime, marine electronics industry body.
Civil twilight: Sun 0-6° below horizon.
Closing speed: Rate of decrease of range to target.
Co-altitude: Complement of celestial altitude.
Coastal traffic zone: Inshore zone seaward of TSS.
COLREGs (72): Convention on the International Regulations for Preventing Collisions at Sea.
Compass course: Course referenced to compass north.
Compass deviation: Difference between magnetic and compass north.
Compass error: Combined deviation and variation.
Composite group flashing light: Light with groups of differing flash counts.
Constant heading line (loxodrome): Rhumb line of constant true course.
Continuous Synopsis Record (CSR): Required under SOLAS XI-1/5.
CPA (Closest Point of Approach): Minimum predicted range to a target.

D

Datum reset (ECDIS): Operation to update WGS-84 datum offsets.
Dead reckoning (DR): Position by course and speed without external fix.
Deck log: Official bridge log book.
Declination (dec): Celestial latitude of a body.
Deep-sea lead: Hand sounding lead, historical practice.
Departure (dep): Easting in plane sailing.
Depth contour line: Isobath on the nautical chart.
Deviation card: Compass deviation table for the magnetic compass.
DGNSS RTCM SC-104: Correction format for differential GNSS.
DGPS: Differential GPS using IALA radio beacons.
Differential Loran: Legacy differential terrestrial radionavigation.
DSC (Digital Selective Calling): GMDSS distress alerting on VHF/MF/HF.
DSC controller: Built-in or standalone DSC modem.

E

ECDIS: Electronic Chart Display and Information System per IMO MSC.232(82).
ECDIS backup arrangement: Type-approved secondary means per SOLAS V/19.
Echo sounder: Acoustic depth sensor.
ECS: Electronic Chart System (non-mandatory).
EGNOS: European SBAS augmentation system.
Electronic Navigational Chart (ENC): S-57 vector chart format.
Ephemeris: Tabulated celestial positions.
EPIRB: Emergency Position-Indicating Radio Beacon required under SOLAS IV/7.
Equation of time: Difference between mean and apparent solar time.
Equinox: Vernal/autumnal crossing of the celestial equator.
Estimated position (EP): DR position corrected for set and drift.
Estimated Time of Arrival (ETA): Predicted time of arrival.

F

FCC ECDIS test set: Type-approval test data set per IHO S-64.
Fix interval: Time between successive position fixes.
Flag signaling: International code of signals (INTERCO).
Forenoon watch: 0800-1200 watch.
Frequency band (Marine VHF): 156-174 MHz channels per ITU-R M.1084.

G

Galileo (GNSS): European Global Navigation Satellite System.
Geo-stationary satellite: Satellite at 35,786 km, used for Inmarsat C.
Geomagnetic equator: Magnetic equator differing from geographic.
Geometric Dilution of Precision (GDOP): GNSS position-accuracy metric.
GLONASS: Russian GNSS constellation.
GMDSS: Global Maritime Distress and Safety System under SOLAS Chapter IV.
Gnomonic chart: Great-circle-as-straight-line chart projection.
GPS L1 C/A: Civilian GPS signal on 1575.42 MHz.
Great circle: Circle on a sphere passing through the center.
Greenwich Hour Angle (GHA): Hour angle measured from Greenwich.
Greenwich Mean Time (GMT/UT1): Mean solar time at Greenwich.
Groundwave (HF): Surface propagation path of HF/MF radio.
GZ curve (collision avoidance): Misnomer; see relative motion plotting.

H

Half convergency correction: Correction in great-circle bearings to chart.
Haversine formula: Spherical trig relation used in distance/bearing.
Heading sensor (THD): Transmitting heading device per IMO MSC.116(73).
Heave-to: Maneuver to hold position in heavy weather.
Hour angle: Angular distance west of meridian.
Hydrographic Office: National hydrographic agency producing charts.
Hydrography: Science of surveying water bodies.

I

IALA Buoyage System (A & B): Regional lateral-buoy color schemes.
IBS (Integrated Bridge System): SOLAS/IMO MSC.252(83) integrated navigation system.
IHO S-100: Universal Hydrographic Data Model.
IHO S-101: Next-generation ENC specification.
IHO S-102: Bathymetric Surface product specification.
IHO S-104: Water Level Information product spec.
IHO S-111: Surface Currents product spec.
IHO S-57: ENC product specification, edition 3.1.
IMO COLREG Rule 13: Overtaking.
IMO COLREG Rule 14: Head-on situation.
IMO COLREG Rule 15: Crossing situation.
IMO COLREG Rule 19: Conduct in restricted visibility.
IMO COLREG Rule 7: Risk of collision determination.
IMO COLREG Rule 8: Action to avoid collision.
Inertial Navigation System (INS): Self-contained dead-reckoning system.
Inshore Traffic Zone: Defined zone between TSS and coast.
Intercept method (Marc St. Hilaire): Standard sight reduction technique.
International Code of Signals (INTERCO): Standard flag and Morse signaling.
Isobar: Line of equal atmospheric pressure on synoptic chart.
Isogonic line: Line of equal magnetic variation.

J

J/T plot (relative): Time-versus-bearing plot of ARPA targets.
Jeppesen RoutePlan: Voyage planning service used commercially.
Junction buoy: Preferred-channel buoy.

K

K-charts: Korean Hydrographic charts.
Karteikomet: Historic chart marker, now archaic.
Knot: One nautical mile per hour.

L

Landfall: First sighting of land after ocean passage.
LAT (Lowest Astronomical Tide): Modern chart datum.
Lateral mark (IALA): Port/starboard channel mark.
Latitude by Polaris: Latitude derived from altitude of Polaris.
Lay course: Course steered along a planned leg.
Leg distance: Distance between two waypoints on the passage plan.
LOA waypoint: Wheelover/initial-turn point.
Local Hour Angle (LHA): Hour angle measured from observer's meridian.
Logbook (Master): Master's official log per SOLAS V/28.
Long-Range Identification and Tracking (LRIT): Required under SOLAS V/19-1.
Loran-C: Legacy hyperbolic radionavigation system.
Loxodrome: Rhumb line.
Lubber line: Reference line on compass aligned with ship's head.

M

Magnetic compass: Standard magnetic compass per ISO 449.
Magnetic variation: Angle between true and magnetic north at a location.
Marine VHF Channel 16: International distress and calling channel.
Marine VHF Channel 70: DSC calling channel.
MARS (Mariners Alerting and Reporting Scheme): Nautical Institute reporting scheme.
MarSEA software: Voyage planning and weather routing software.
Mean sea level (MSL): Average level of the sea surface.
Mercator projection: Conformal chart projection with rhumb lines as straight.
Meridian altitude: Altitude of body on observer's meridian.
Meridian passage (LAN): Transit of body across observer's meridian.
MMSI: Maritime Mobile Service Identity, 9-digit per ITU-R M.585.
Mob (Man Overboard): MOB drill/COB procedure.
Movement direction (compass): Magnetic, true, or compass reference.

N

Nakhoda's logbook: Historic master's log.
Nautical Almanac: Annual joint UK/US publication.
Nautical mile: 1852 m international nautical mile.
Navigation Warning (NAVAREA): Worldwide navigation warning service.
NAVTEX: GMDSS broadcast service under SOLAS IV.
Newman's nomenclature (radar): Plotting nomenclature O, T, M.
NMEA 0183: Marine electronics serial data standard.
NMEA 2000: CAN-based marine data network.
No-go area: Area on passage plan excluded from passage.
Noon position: Daily fix near LAN reported to the company.

O

Observed altitude (Ho): Sextant altitude corrected for index, refraction, dip.
Ocean current chart: Pilot chart with ocean currents.
Offshore Service Vessel (OSV): Specialized class with own nav considerations.
One-man bridge operation (OMBO): DNV class notation requiring redundancy.
Overfalls: Steep choppy seas at tidal races marked on charts.

P

Parallel index (PI): Radar parallel-indexing technique.
Parallel of latitude: Small circle parallel to the equator.
Parallel rulers: Bridge plotting instrument.
Passage plan (Berth-to-Berth): Appraisal-Planning-Execution-Monitoring per A.893(21).
Phase code (light): Coded sequence of light character.
Pilot card: Standard A4 card given to pilot.
Pilotage: Conduct of vessel by a licensed pilot.
PRC (Pseudo-Range Correction): Differential GNSS correction.
Preferred channel buoy: Buoy at channel junction.
Pressure pattern (synoptic): High/low pressure system distribution.

Q

Quadrantal correctors: Soft-iron spheres on magnetic compass binnacle.
Quartermaster: Helmsman on watch.

R

Racon: Radar transponder marking AtoNs.
Radar mile: 6.18 microseconds round-trip time.
Radar plotting sheet: Manoeuvring board used for manual plotting.
Range light: Two fixed lights in line indicating channel.
Reefing: Reducing sail area in heavy weather.
Refraction (electromagnetic): Bending of radar/visual rays.
Relative wind: Wind as seen from moving vessel.
Restricted in ability to manoeuvre (RAM): COLREGs status.
Right ascension (RA): Equatorial coordinate of celestial body.
Rolling hitch: Knot used to take strain on tensioned line.
Route monitoring (ECDIS): Display of own ship on planned route.
Rule 5 (lookout): COLREGs requirement for proper lookout.

S

Safety contour (ECDIS): Operator-selected depth contour.
Safety depth (ECDIS): Sounding alarm threshold.
SAR Convention: Search and Rescue Convention 1979.
SART (Search and Rescue Transponder): 9 GHz radar transponder per IMO Res. A.802(19).
SBAS (Satellite-Based Augmentation System): WAAS/EGNOS/MSAS GNSS augmentation.
Seakeeping limit (master's discretion): Operational limits in heavy weather.
Set and drift: Vector of current affecting DR.
Sextant: Marine sextant with vernier or micrometer.
Ship's noon report: Daily report of position, fuel, speed.
Sight reduction tables (HO 229, HO 249): Tabular sight reduction.
SIRENAC: Paris MoU PSC inspection database.
SOLAS V/19: Carriage requirements for navigational equipment.
SOLAS V/22: Bridge visibility requirements.
SOLAS V/34: Voyage planning requirement.
Sound signal: Whistle, gong, or bell signal per COLREGs Annex III.
Speed log (Doppler): Acoustic speed-through-water and over-ground sensor.
Squat: Loss of underkeel clearance due to speed in shallow water.
Stand-on vessel: COLREGs vessel required to maintain course.
Standard organization of bridge watch: STCW Section A-VIII/2 part 4-1.
STCW Code: Standards of Training Certification and Watchkeeping.
Strapped-down INS: INS with no mechanical gimbals.

T

TCPA (Time to CPA): ARPA-computed time to closest point.
Tidal harmonic constituents: M2, S2, N2, K1, O1, etc.
Tidal stream atlas: Admiralty tidal stream publication.
Tide gauge: Instrument recording sea-surface elevation.
Time zone (ship): Hour-based time zone used at sea.
TPL (Total Power Loss): Operational concept in blackout response.
Track control system: ECDIS-coupled track autopilot per MSC.74(69).
Track spacing (sounding survey): Hydrographic survey line spacing per IHO S-44.
Traffic Separation Scheme (TSS): Routeing measure per Ships' Routeing.
Transit fix: Position from two natural ranges in line.
True bearing: Bearing referenced to true north.
True course: Course referenced to true north.
TSS Inshore Traffic Zone: Restricted-use zone landward of separation line.

U

UKC (Under Keel Clearance): Vertical distance keel-to-seabed.
Universal Time Coordinated (UTC): Reference timescale for navigation.
Upwelling: Coastal current rising cold water, relevant in weather routing.

V

Variation (magnetic): Angle between true and magnetic north.
VDR (Voyage Data Recorder): SOLAS V/20 mandated black box per MSC.333(90).
Vertex (great circle): Highest latitude on a great-circle track.
Visibility (meteorological): Maximum horizontal distance objects can be seen.
Visual fix: Position from two or more visual bearings.
VTS (Vessel Traffic Services): SOLAS V/12 traffic monitoring service.

W

Watchkeeping arrangements: Schedules in compliance with STCW VIII.
Weather routing: Optimum-track routing per environmental forecasts.
Weather window: Period of suitable weather for an operation.
WGS-84: World Geodetic System 1984, GNSS datum.
Wheelover position: Calculated position to commence turn to new course.
Wind chill chart: Used for crew safety planning.
WMO (World Meteorological Organization): Standards for sea/weather observations.
WWNWS (World-Wide Navigation Warning Service): NAVAREA coordinator.

X

X-band radar: 9.4 GHz band marine radar.

Y

Yawmeter: Sensor measuring yaw rate, integrated with autopilot.

Z

Z-time: Synonym for UTC.
Zenith: Point on celestial sphere directly overhead.
Zenith distance: 90° minus altitude.
Zone description: Integer hours offset from UTC at sea.

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