35 terms in this category.
- Automatic Identification System
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°.
- 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.
- 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
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
A navigation information system that displays ENCs and vessel position, accepted as a replacement for paper charts under SOLAS.
- Estimated Position
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
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.
- Gyrocompass
A compass using a gyroscope to find geographic north, unaffected by magnetic fields; mandatory on most large vessels.
- Intercept
In celestial navigation, the difference in minutes of arc between the observed altitude and the calculated altitude, used to plot a position line.
- 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.
- Parallel Index
A radar technique using lines parallel to the course line to monitor closest approach to a fixed radar target.
- 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
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.