Pancyprian Compass & Instruments flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Sextant index error
- The error of a sextant when the index and horizon mirrors are parallel; if on the arc it is subtracted from readings, if off the arc it is added.
- Sextant vernier scale
- A auxiliary scale on a sextant that subdivides the main arc to read angles to 0.1 or 0.2 minutes of arc, improving precision.
- Aneroid barometer
- A pressure instrument using a sealed flexible capsule that expands and contracts with atmospheric pressure, moving a pointer on a graduated dial.
- Chronometer rate
- The daily gain or loss of a chronometer, determined by comparison with time signals; it is applied to chronometer time to obtain accurate UT.
- Echo sounder principle
- Depth is found by measuring the time for an acoustic pulse to travel to the seabed and back; depth equals sound velocity times time divided by two.
- Doppler log
- A speed log that measures speed over ground by the frequency shift of acoustic pulses reflected from the seabed, independent of water movement.
- Magnetic compass directive force
- The horizontal component of Earth's magnetic field that aligns the compass needle; it decreases with increasing magnetic latitude and dip.
- Gyrocompass north-seeking
- The property of a gyrocompass whereby Earth's rotation and gravity cause the spin axis to settle in the true meridian, indicating true north.
- Gyrocompass settling time
- The period, typically one to four hours, required after starting for a gyrocompass to settle and indicate true north accurately.
- Compass deviation
- The angle between compass north and magnetic north caused by the vessel's own magnetic field; it varies with heading and is recorded on a deviation card.
- Magnetic variation
- The angle between magnetic north and true north at a given place and time, shown on charts and subject to slow annual change.
- Gyrocompass latitude error
- An error of a gyrocompass that increases with latitude because the horizontal component of Earth's rotation, which provides the north-seeking force, becomes small.
- Compass error formula
- True bearing equals compass bearing plus deviation plus variation, with east positive and west negative; compass error is the algebraic sum of deviation and variation.
- Deviation card
- A table or curve showing residual deviation on each compass heading after adjustment, used to convert compass bearings to magnetic or true bearings.
- Agonic line
- The line on a chart joining places of zero magnetic variation, where magnetic north and true north coincide.
- Isogonic line
- A line on a chart connecting places of equal magnetic variation, used to determine variation at a position.
- Gyrocompass speed error
- An error caused by the vessel's motion, proportional to speed times cosine of latitude, maximum on north-south courses and zero on east-west courses.
- Semicircular deviation
- Deviation caused by permanent magnetism and horizontal soft iron, changing sign between north and south or east and west headings; corrected by permanent magnets.
- Quadrantal deviation
- Deviation caused by horizontal soft iron, varying with twice the heading and corrected by soft iron spheres or correctors in the binnacle.
- Flinders bar
- A soft iron corrector in the binnacle that compensates for quadrantal deviation caused by vertical soft iron, such as funnels and masts, especially after latitude changes.
- Heeling error
- Deviation caused by vertical permanent magnetism when the vessel heels; corrected by a vertical magnet in the binnacle and checked after large latitude changes.
- Swinging the compass
- The procedure of turning the vessel through 360 degrees to observe and record deviation on various headings, used to produce a deviation card.
- Compass binnacle
- The housing for a magnetic compass containing corrector magnets and soft iron spheres, mounted on the centreline away from magnetic influences.
- Compass gimbals
- A mounting with two perpendicular horizontal axes that keeps the compass card horizontal as the vessel rolls and pitches.
- Lubber line
- A vertical line or mark on the compass bowl aligned with the vessel's fore-and-aft line, at which the compass heading is read.
- Compass liquid bubble
- A bubble in the compass bowl indicating low liquid or a leak; it impairs damping and accuracy and should be rectified by a compass adjuster.
- Gyrocompass repeater
- A remote display that receives heading signals from the master gyrocompass and repeats the heading at the steering position and bridge wings.
- Compass correction magnets
- Permanent magnets placed in the binnacle fore-and-aft and athwartships to correct semicircular deviation; a vertical magnet corrects heeling error.
- Dip of the horizon
- The angle between the horizontal and the visible horizon, caused by the observer's height above sea level; it is subtracted from sextant altitude.
- Celestial refraction correction
- A correction applied to observed altitude because light from a celestial body bends in the atmosphere, making the body appear higher than its true position.
- Barograph
- A recording barometer that continuously traces atmospheric pressure on a rotating drum, used to detect developing weather systems.
- Psychrometer
- An instrument with wet-bulb and dry-bulb thermometers; the difference in readings gives relative humidity and dew point when used with tables.