Charts, position-fixing, watchkeeping, COLREG. Bridge-side terminology — celestial, electronic, coastal.
51 terms in this category.
- Automatic Identification System (AIS)
VHF transponder system that automatically broadcasts vessel identity, position, course, and speed to nearby ships and shore stations.
- Azimuth
The angular bearing of a celestial body measured clockwise from true north, used to check compass error.
- Bearing
The horizontal direction of one point from another, expressed in degrees from 000° to 359°.
- Bergy Bit
Medium fragment of glacier ice, 1–5 m above water and 5–15 m across.
- Celestial Navigation
The art and science of determining a vessel's position by measuring the altitudes of celestial bodies with a sextant.
- Chronometer
A precision timekeeping instrument used in celestial navigation to provide accurate GMT for the calculation of longitude.
- Clearing Line
A bearing or line on the chart that, when maintained, keeps a vessel clear of a specific hazard such as a shoal or reef.
- COLREG Rule 13 — Overtaking
Any vessel overtaking another shall keep out of the way of the vessel being overtaken — applies regardless of relative status under other rules.
- COLREG Rule 14 — Head-On
When two power-driven vessels meet on reciprocal courses, each shall alter course to starboard.
- COLREG Rule 15 — Crossing
When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way.
- COLREG Rule 18 — Responsibilities
Hierarchy of stand-on / give-way: power-driven vessels give way to sailing, sailing to fishing, fishing to NUC and RAM.
- COLREG Rule 19 — Restricted Visibility
Conduct of vessels in or near restricted visibility — early action, safe speed, and avoidance of port-side alterations to a vessel forward of the beam.
- COLREG Rule 5 — Lookout
Every vessel shall at all times maintain a proper lookout by sight and hearing as well as by all available means appropriate.
- COLREG Rule 6 — Safe Speed
Every vessel shall proceed at a safe speed so she can take proper and effective action to avoid collision.
- COLREG Rule 7 — Risk of Collision
Every vessel shall use all available means to determine if risk of collision exists; if in doubt, such risk shall be deemed to exist.
- Compass
Instrument indicating direction relative to magnetic north or true north, fundamental to ship navigation.
- Compass Bearing
A bearing measured by a ship's compass, requiring correction for both variation and deviation to obtain a true bearing.
- Danger Angle
A horizontal or vertical sextant angle that, when not exceeded, ensures a vessel remains clear of a coastal hazard.
- Dead Reckoning (DR)
Calculating current position using a known past position, then advancing it using speed, course, and elapsed time.
- Deviation
The error in a magnetic compass caused by the ship's own magnetic field, varying with the vessel's heading.
- Deviation Card
A tabulated record of a magnetic compass's deviation on successive headings, prepared after compass adjustment or swing.
- Electronic Chart Display and Information System (ECDIS)
A navigation information system that displays ENCs and vessel position, accepted as a replacement for paper charts under SOLAS.
- Estimated Position (EP)
A position obtained by advancing a known fix using course and speed while applying estimated leeway and current allowances.
- Fix
A confirmed vessel position established by two or more simultaneous position lines from observed bearings, ranges, or electronic navaids.
- Global Positioning System (GPS)
US satellite-based radionavigation system providing position, velocity, and time data worldwide to marine and other users.
- Great Circle
The shortest route between two points on a sphere, formed by the intersection of the sphere and a plane through its center.
- Growler
Small piece of glacier ice (<1 m above water, ~5 m across) — particularly dangerous because it is hard to detect on radar.
- Gyrocompass
A compass using a gyroscope to find geographic north, unaffected by magnetic fields; mandatory on most large vessels.
- Iceberg
Mass of glacier ice >5 m above the water, classified small/medium/large/very large by IIP.
- Intercept
In celestial navigation, the difference in minutes of arc between the observed altitude and the calculated altitude, used to plot a position line.
- Lead
Linear crack or fracture in sea ice large enough for navigation.
- Leading Line
Two charted objects in line that define a safe course into or within a port, keeping the vessel clear of hazards.
- Loxodrome
A line on the earth's surface crossing all meridians at the same angle, synonymous with a rhumb line course.
- Magnetic Bearing
A bearing measured clockwise from magnetic north, requiring correction for variation to obtain a true bearing.
- Magnetic Compass
A compass that aligns with Earth's magnetic field to indicate magnetic north; required as backup on all SOLAS vessels.
- Mercator Sailing
A method of solving rhumb line problems using the properties of a Mercator chart to find course and distance between positions.
- Northern Sea Route (NSR)
Russian Arctic shipping route along Siberia from Kara Gate to Bering Strait; transits regulated by Glavsevmorput (NSR Administration).
- Not Under Command (NUC)
Vessel which through exceptional circumstance cannot manoeuvre as required by the rules; shows two black balls / two red lights vertically.
- Parallel Index (PI)
A radar technique using lines parallel to the course line to monitor closest approach to a fixed radar target.
- Polynya
Persistent area of open water surrounded by sea ice, shaped by wind/current or upwelling.
- Restricted in Ability to Manoeuvre (RAM)
Vessel which from the nature of her work is restricted in her ability to manoeuvre; shows ball-diamond-ball / R-W-R lights.
- Rhumb Line
A course that crosses all meridians at the same angle, appearing as a straight line on a Mercator chart.
- Running Fix
A position obtained from two or more bearings of the same object taken at different times and advanced along the course line.
- Sextant
A precision optical instrument used to measure the angle between a celestial body and the horizon for position fixing.
- Sight Reduction
The mathematical process of converting a celestial observation into a position line using tables or a calculator.
- Three-Point Bearing
A position fix obtained by simultaneously measuring horizontal angles between three charted objects using a sextant or compass.
- Transit
Two or more objects in line with each other, used as a position line or to verify vessel alignment in a channel.
- True Bearing
A bearing measured clockwise from true north, used for chart plotting and unaffected by magnetic variation or compass deviation.
- Variation
The angular difference between true north and magnetic north at a given location, shown on navigational charts.
- Voyage Data Recorder (VDR)
A tamper-proof device recording bridge audio, radar images, and navigational data onto a protected capsule for post-incident investigation.
- Weather Routing
A service providing vessel operators with recommended routes based on forecast weather and sea conditions to optimise safety and economy.