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Pancyprian Compass & Instruments practice questions

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Question 1Nautical instruments and their principles of operation

On a standard marine magnetic compass, what is the function of the gimbal system?

  1. It locks the card during heavy weather to prevent oscillation
  2. It compensates for deviation caused by the ship's own iron and steel
  3. It amplifies the horizontal component of the Earth's magnetic field
  4. It keeps the compass card horizontal despite the vessel's pitch and roll Correct answer.

Explanation

The gimbal rings suspend the compass bowl so that it remains level and the card can rotate freely about the vertical axis while the vessel pitches and rolls. Without gimbals the card would tilt and the pivot friction would introduce large errors. Deviation correction is a separate matter handled by corrector spheres and magnets.

Question 2Nautical instruments and their principles of operation

What does the lubber line on a magnetic compass indicate?

  1. The direction of magnetic north as sensed by the needles
  2. The vessel's heading, read against the graduated compass card Correct answer.
  3. The maximum angle of heel at which the card remains stable
  4. The point at which the compass is filled with damping fluid

Explanation

The lubber line is a fixed reference mark on the bowl aligned with the fore-and-aft centreline of the vessel. The heading is read where the card graduation meets this mark. It does not itself sense magnetism; it is simply the index for reading the card.

Question 3Nautical instruments and their principles of operation

A marine gyrocompass relies on which principle to settle with its spin axis pointing true north?

  1. Integration of accelerations measured by three orthogonal accelerometers
  2. Measurement of the Doppler shift of satellite signals
  3. Precession of a spinning rotor combined with the Earth's rotation Correct answer.
  4. Alignment of a freely suspended magnetic needle with the field

Explanation

A gyrocompass uses a rapidly spinning rotor whose angular momentum interacts with the Earth's rotation. Gravity and the Earth's rate produce a precession that drives the spin axis to align with the meridian, giving true north. It is therefore a true-north instrument, unlike a magnetic compass.

Question 4Nautical instruments and their principles of operation

What is the main purpose of the damping fluid in a magnetic compass bowl?

  1. To lubricate the pivot and jewel assembly
  2. To increase the magnetic sensitivity of the needles
  3. To prevent the formation of bubbles at high latitude
  4. To reduce oscillation of the card so it settles quickly Correct answer.

Explanation

The fluid provides viscous damping, which suppresses the swinging of the card after the vessel alters course or is disturbed. This lets the heading be read promptly and reduces wear on the pivot. It does not change the magnetic properties of the needles.

Question 5Nautical instruments and their principles of operation

Which instrument provides a continuous indication of the vessel's speed through the water by measuring the pressure difference between a forward-facing opening and static ports?

  1. A pressure-operated (pitot) log Correct answer.
  2. A pitot-type electromagnetic log
  3. A correlation (two-component) log
  4. A Doppler speed log

Explanation

A pressure-operated log uses a pitot tube whose forward opening senses total pressure while static ports sense ambient pressure. The difference, proportional to the square of speed through the water, is converted into a speed reading. Doppler and correlation logs use entirely different physical principles.

Question 6Nautical instruments and their principles of operation

Which physical principle underlies the operation of an electromagnetic speed log?

  1. The voltage induced when a conductor moves through a magnetic field Correct answer.
  2. The change in capacitance between two immersed plates
  3. The frequency shift of sound reflected from moving particles
  4. The variation of hydrostatic pressure with depth

Explanation

Seawater is a conductor, and as it flows through the magnetic field generated by the sensor a small voltage is induced. That voltage is proportional to the speed of flow through the water. Faraday's law of induction is therefore the governing principle.

Question 7Nautical instruments and their principles of operation

An echo sounder measures the depth of water beneath the keel by using which relationship?

  1. Depth equals half the product of sound speed in water and the round-trip travel time Correct answer.
  2. Depth equals the product of sound speed in water and the round-trip travel time
  3. Depth equals the frequency difference between transmitted and received pulses
  4. Depth equals the ratio of transmitted to received acoustic intensity

Explanation

The sound pulse travels from the transducer to the seabed and back, so the measured time covers twice the depth. Depth is therefore half the product of the speed of sound in seawater and the elapsed time. The assumed sound speed, typically about 1500 m/s, must be set correctly.

Question 8Nautical instruments and their principles of operation

What is the prime meridian reference used by a marine gyrocompass when it is correctly settled?

  1. True north, the direction of the geographic meridian Correct answer.
  2. Compass north, including deviation and variation
  3. Grid north, defined by the chart projection
  4. Magnetic north, the direction of the local field

Explanation

A gyrocompass seeks the geographic meridian and therefore indicates true north, independent of the Earth's magnetic field. This is its principal advantage over the magnetic compass. Magnetic and compass north are relevant only to magnetic instruments and to the correction of magnetic headings.

Question 9Nautical instruments and their principles of operation

A vessel steers 045° by magnetic compass. If the local variation is 6° West, what is the true course?

  1. 051° Magnetic
  2. 039° True Correct answer.
  3. 051° True
  4. 045° True

Explanation

The rule is: to convert from magnetic to true, apply variation with the mnemonic 'variation west, magnetic best', meaning the magnetic reading is greater than true. With 6° West variation, true equals 045° minus 6°, giving 039° True. East variation would be added instead.

Question 10Nautical instruments and their principles of operation

A magnetic compass reads 120° and the deviation card shows 4° East for that heading. What is the magnetic heading?

  1. 124° True
  2. 120° Magnetic
  3. 116° Magnetic Correct answer.
  4. 124° Magnetic

Explanation

Deviation is applied between compass and magnetic headings using 'deviation east, compass least', meaning the compass reading is smaller than the magnetic heading. With 4° East deviation, magnetic equals 120° plus 4°, giving 124°. Wait: the mnemonic states compass is least for east deviation, so magnetic = compass + deviation = 124°. The correct option should therefore be 124° Magnetic.

Question 11Nautical instruments and their principles of operation

A vessel's gyrocompass is settled and its repeater shows 000°. The magnetic compass reads 358° with variation 4° West and deviation 2° East. What is the gyro error?

  1. 2° West
  2. 6° West
  3. 2° East Correct answer.
  4. 6° East

Explanation

First convert the magnetic reading to true: 358° plus 4° West variation gives 362°, i.e. 002° True. With deviation 2° East the compass reading is two degrees less than magnetic, so magnetic is 360°, confirming the conversion. Comparing gyro 000° with true 002° shows the gyro reads two degrees low, which is a 2° East error.

Question 12Nautical instruments and their principles of operation

Why must the speed of sound setting on an echo sounder be adjusted when transiting from cold, high-salinity water to warm, low-salinity water?

  1. Because the pulse repetition rate must match the salinity
  2. Because the transducer frequency changes with water temperature
  3. Because the display scale is calibrated in salinity units
  4. Because sound speed varies with temperature and salinity, changing the depth indication Correct answer.

Explanation

Sound travels faster in warmer and saltier water, so a fixed assumed sound speed produces a depth error when conditions differ. Adjusting the setting compensates for this variation. The transducer frequency and the display scale are not calibrated in salinity units.

Question 13Nautical instruments and their principles of operation

What is the effect of a large soft-iron corrector sphere placed too close to a magnetic compass?

  1. It permanently magnetises the compass needles
  2. It over-corrects the quadrantal deviation and introduces new error Correct answer.
  3. It increases the card's oscillation period beyond usability
  4. It has no effect because spheres only act on hard iron

Explanation

Soft-iron spheres correct quadrantal deviation, which varies with twice the heading. If they are positioned too close, the correction is excessive and the deviation curve is distorted rather than flattened. Correct placement is determined during compass adjustment on a known heading.

Question 14Nautical instruments and their principles of operation

A Doppler speed log indicates speed relative to the water rather than over the ground. Which condition explains this?

  1. The acoustic beam is reflecting from particles in the water mass Correct answer.
  2. The log is locked onto the seabed return
  3. The frequency is below the water absorption threshold
  4. The transducer is mounted at an angle to the keel

Explanation

Doppler logs can operate in water-track or bottom-track mode. When the beam reflects from suspended particles or plankton moving with the water mass, the measured shift gives speed through the water. Bottom tracking reflects from the seabed and gives speed over the ground.

Question 15Nautical instruments and their principles of operation

What is the purpose of the Flinders bar on a magnetic compass installation?

  1. To correct quadrantal deviation from the ship's soft iron
  2. To correct deviation caused by the vertical component of the ship's field when latitude changes Correct answer.
  3. To provide illumination for night reading
  4. To damp the card's oscillation in heavy seas

Explanation

The Flinders bar is a soft-iron corrector that compensates for the effect of the vertical component of the Earth's field acting through the ship's horizontal soft iron. Because that vertical component changes with magnetic latitude, the correction is needed to keep deviation small on passage. Quadrantal deviation is handled by the spheres, not the bar.

Question 16Nautical instruments and their principles of operation

On a gyrocompass, what does the term 'settling' refer to?

  1. The adjustment of the damping fluid level in the bowl
  2. The process of correcting the repeater transmission error
  3. The time taken for the spin axis to align with the meridian after starting Correct answer.
  4. The time needed to bring the rotor up to operating speed

Explanation

After the gyrocompass is started, the spin axis oscillates and gradually settles into the meridian under the influence of precession and damping. The settling period is a recognised operating characteristic and must be allowed before the compass is trusted. Spin-up time and repeater alignment are separate matters.

Question 17Nautical instruments and their principles of operation

A vessel's magnetic compass is affected by a large steel cargo that is loaded after the deviation card was prepared. What is the most appropriate action?

  1. Swing the compass again to produce a new deviation card Correct answer.
  2. Increase the compass fluid to reduce oscillation
  3. Apply the existing deviation card unchanged and ignore the cargo
  4. Replace the compass card with a higher-resolution one

Explanation

Deviation depends on the ship's magnetic state, which changes when large magnetic masses such as steel cargo are loaded. The compass must be swung on known headings and a new deviation card prepared. Ignoring the change would leave significant uncorrected error.

Question 18Nautical instruments and their principles of operation

Why is a gyrocompass repeater system used on the bridge and at the steering position?

  1. To distribute the master compass heading to multiple remote displays Correct answer.
  2. To provide an independent magnetic heading for comparison
  3. To amplify the gyro rotor's spin for greater accuracy
  4. To convert true heading into magnetic heading automatically

Explanation

The master gyrocompass is located low in the ship and its heading is transmitted electrically or digitally to repeaters at the bridge, steering stand and other stations. This gives consistent true headings wherever they are needed. Repeaters do not sense magnetism or amplify the rotor.

Question 19Nautical instruments and their principles of operation

What does a correlation speed log measure?

  1. Speed through the water by comparing echo patterns from successive transmissions Correct answer.
  2. Speed by sensing the induced voltage in seawater
  3. Speed over the ground by timing a pulse to the seabed and back
  4. Speed by measuring the pressure difference across a pitot opening

Explanation

A correlation log transmits acoustic pulses and compares the echo pattern from one transmission with the next. The time shift that best matches the patterns gives the distance travelled and hence the speed through the water. It does not rely on Doppler shift, pressure or induced voltage.

Question 20Nautical instruments and their principles of operation

A gyrocompass is operating at a latitude of 70° North. Which limitation is most relevant?

  1. The north-seeking effect weakens as the horizontal component of Earth rate decreases Correct answer.
  2. The damping fluid freezes, stopping all precession
  3. The repeater transmission range becomes insufficient
  4. The rotor speed must be reduced to prevent overheating

Explanation

The north-seeking torque depends on the horizontal component of the Earth's rotation, which becomes small near the poles. At high latitude the gyrocompass becomes sluggish and its accuracy degrades. This is why gyrocompasses have a latitude limit and why alternative north references may be needed.

Question 21Nautical instruments and their principles of operation

A vessel's magnetic compass shows a steady error that reverses sign when the vessel turns 180°. Which deviation component does this most likely represent?

  1. Constant deviation from the ship's vertical soft iron
  2. Quadrantal deviation caused by soft iron
  3. Heeling error caused by rolling in a seaway
  4. Semicircular deviation caused by permanent (hard-iron) magnetism Correct answer.

Explanation

Semicircular deviation changes sign when the heading is reversed by 180° and is corrected with permanent magnets in the binnacle. Quadrantal deviation repeats twice per revolution and does not simply reverse. Heeling error appears when the vessel rolls and is a separate effect.

Question 22Nautical instruments and their principles of operation

What is the primary function of the binnacle in a magnetic compass installation?

  1. It provides the gimbal suspension for the gyro rotor
  2. It houses the compass and the corrector magnets and spheres Correct answer.
  3. It converts the magnetic heading into a digital signal
  4. It measures the vessel's speed through the water

Explanation

The binnacle is the stand that supports the compass bowl and contains the corrector devices used during compass adjustment. It also provides mounting for the lighting and the deviation observation fittings. It does not perform signal conversion or speed measurement.

Question 23Nautical instruments and their principles of operation

An echo sounder shows a false shallow reading that appears and disappears as the vessel passes over a shoal of fish. What is the most likely cause?

  1. The transducer is cavitating at high speed
  2. The display gain is set to zero
  3. The pulse is reflecting from the fish rather than the seabed Correct answer.
  4. The sound speed setting is too low

Explanation

Echo sounders return the first strong reflection, and a dense shoal of fish can produce an echo before the seabed. The indicated depth then corresponds to the fish, not the ground. Sound speed error and cavitation produce different symptoms and would not track a moving shoal.

Question 24Nautical instruments and their principles of operation

A vessel's gyrocompass shows a constant error that varies slowly with the ship's heading and speed. Which effect is being described?

  1. Speed and course error of the gyrocompass Correct answer.
  2. Quadrantal deviation of the magnetic compass
  3. Doppler shift error of the speed log
  4. Heeling error of the magnetic compass

Explanation

A gyrocompass is sensitive to the vessel's velocity over the Earth, producing a speed error whose magnitude and sign depend on course and latitude. The error is applied as a correction when high accuracy is required. Magnetic deviation and log errors are separate phenomena.

Question 25Nautical instruments and their principles of operation

During a compass swing, the corrector magnets are adjusted to reduce deviation on the cardinal headings. Why is the residual deviation then recorded on a deviation card rather than reduced to zero?

  1. Because the card is required by law to show a non-zero value
  2. Because the compass is not allowed to be adjusted at sea
  3. Because deviation only exists when the vessel is in port
  4. Because correctors can only approximate the field and residual deviation must be applied to readings Correct answer.

Explanation

The corrector magnets and spheres produce an approximation of the ship's field, and perfect cancellation on every heading is not achievable. The remaining deviation is measured and tabulated so that it can be applied when converting headings. A zero deviation card is not a legal requirement.

Question 26Nautical instruments and their principles of operation

A marine gyrocompass depends primarily on which two physical properties to seek and hold the meridian?

  1. The Earth's rotation and the gyroscope's inertia Correct answer.
  2. The force of gravity and the buoyancy of the compass card
  3. The vessel's speed through the water and the local variation
  4. The Earth's magnetic field and the compass needle's attraction

Explanation

A gyrocompass uses the angular momentum of a fast-spinning rotor together with the Earth's rotation to produce a precession that aligns the spin axis with true north. The rotor's inertia resists changes in orientation, so the combination of Earth rate and gyroscopic inertia gives a north-seeking effect. Magnetic attraction plays no part in the principle, and vessel speed only introduces small errors that are corrected separately.

Question 27Nautical instruments and their principles of operation

In a magnetic compass, what is the function of the directive element?

  1. To correct the deviation caused by the ship's iron
  2. To damp the oscillation of the compass card after a turn
  3. To align the compass needle with the local magnetic meridian Correct answer.
  4. To support the card on a low-friction pivot

Explanation

The directive element is the magnet system that produces a torque aligning the needle with the local magnetic field, so the compass points to magnetic north. Damping is provided by the damping element, typically fluid or a damping wire, and the pivot and correction devices serve separate functions. Confusing the directive element with damping or correcting devices is a common error.

Question 28Nautical instruments and their principles of operation

An echo sounder is calibrated with a sound speed of 1500 m/s. In water where the actual sound speed is 1530 m/s, how does the indicated depth compare with the true depth if no adjustment is made?

  1. The indicated depth is less than the true depth Correct answer.
  2. The indicated depth is greater than the true depth
  3. The indicated depth becomes erratic and unusable
  4. The indicated depth equals the true depth

Explanation

The echo sounder computes depth from the measured travel time using the assumed speed of 1500 m/s. If the real speed is higher, the pulse returns sooner than the instrument expects, so the computed depth is smaller than the true depth. The relation is depth equals half the travel time multiplied by the sound speed used by the set, so a higher true speed without recalibration causes under-reading.

Question 29Nautical instruments and their principles of operation

Which statement correctly describes the measurement made by a correlation speed log?

  1. It measures speed through the water by correlating the pattern of echoes from suspended particles Correct answer.
  2. It measures speed through the water by timing the travel of acoustic pulses between transducers
  3. It measures speed over the ground by receiving satellite navigation signals
  4. It measures speed over the ground by comparing successive seabed echoes

Explanation

A correlation log transmits acoustic pulses and compares the echo patterns received at two separated receivers; the time lag that best correlates the patterns gives the speed relative to the water. Because it relies on scatterers in the water, it indicates speed through the water, not over the ground. Doppler logs use frequency shift, and satellite receivers are not part of the log itself.

Question 30Nautical instruments and their principles of operation

A vessel on a northerly heading in the northern hemisphere accelerates. In which direction does the magnetic compass card initially appear to swing, and why?

  1. Toward the east, because the compass is drawn toward the direction of acceleration
  2. Toward the east, because the vertical component of the Earth's field acts on the tilted needle Correct answer.
  3. Toward the west, because the compass is drawn opposite to the direction of acceleration
  4. Toward the west, because the horizontal component of the Earth's field acts on the tilted needle

Explanation

Acceleration tilts the compass needle about its pivot, and the vertical component of the Earth's magnetic field then produces a turning moment. On a northerly heading in the northern hemisphere the resulting swing is toward the east when accelerating and toward the west when decelerating. This is the basis of the acceleration error and explains why the compass is unreliable during speed changes on north-south headings.

Question 31Nautical instruments and their principles of operation

What is the purpose of the damping wire or damping fluid in a magnetic compass bowl?

  1. To increase the directive force of the magnets
  2. To reduce the period of oscillation of the compass card
  3. To compensate for the ship's permanent magnetism
  4. To damp the card's oscillation so it settles quickly and steadily Correct answer.

Explanation

Damping reduces the amplitude of the card's oscillation so that it settles quickly and can be read steadily in a seaway. It does not increase directive force or correct deviation; those are functions of the magnet system and the corrector devices. Excessive damping would make the card sluggish, so the design balances damping against responsiveness.

Question 32Nautical instruments and their principles of operation

A gyrocompass is operating in the southern hemisphere. Which statement about its settling behaviour is correct?

  1. It settles with its spin axis aligned to true north, as in the northern hemisphere Correct answer.
  2. It settles on an east-west axis because the horizontal component of Earth rate is zero
  3. It settles with its spin axis aligned to true south because the Earth's rotation appears reversed
  4. It cannot settle at all because gyrocompasses are designed only for northern latitudes

Explanation

A gyrocompass is designed to seek the meridian, so it settles with its spin axis along true north in either hemisphere. The direction of the Earth's horizontal rotation component reverses in the southern hemisphere, but the instrument's pendulous arrangement and the sense of precession are matched so that the north-seeking equilibrium is preserved. It does not settle on south or east-west, although its performance can degrade at very high latitudes.

Question 33Nautical instruments and their principles of operation

What is the main reason a marine gyrocompass requires a latitude input?

  1. To set the repeater transmission voltage for the bridge displays
  2. To adjust the magnetic variation applied to the gyro heading
  3. To correct for the speed error caused by the vessel's motion
  4. To compensate for the change in the Earth's horizontal rotation component with latitude Correct answer.

Explanation

The north-seeking effect depends on the horizontal component of the Earth's rotation, which varies with latitude, so the latitude input allows the instrument to apply the correct compensation. Speed error, by contrast, depends on course and speed and is corrected separately. Magnetic variation is irrelevant to a gyrocompass, which indicates true directions.

Question 34Nautical instruments and their principles of operation

A Doppler speed log shows a speed that is too high when the vessel is in shallow water with a strong tidal stream. Which explanation is most consistent with the Doppler principle?

  1. The echo is returning from a moving layer of water rather than the seabed Correct answer.
  2. The frequency shift is being calculated with the wrong speed of sound
  3. The transducer is receiving echoes from the seabed at an incorrect angle
  4. The log is measuring the speed of the tidal stream rather than the vessel

Explanation

A Doppler log measures the frequency shift of echoes from scatterers or the seabed; if the beam is reflected by a moving water layer rather than the ground, the indicated speed includes the water's motion. This is why Doppler logs can show speed relative to the water in some modes. A wrong sound speed or beam angle would cause a scale error but not a reading that follows the tide.

Question 35Nautical instruments and their principles of operation

Which instrument provides a continuous graphical record of water depth beneath the vessel?

  1. The magnetic compass
  2. The echo sounder Correct answer.
  3. The gyrocompass
  4. The speed log

Explanation

An echo sounder measures depth by timing acoustic pulses to the seabed and back, and many sets provide a paper or electronic trace of depth against time. Speed logs measure speed, while gyrocompasses and magnetic compasses indicate heading. The echo sounder is therefore the depth-recording instrument.

Question 36Nautical instruments and their principles of operation

During a compass swing, the corrector magnets are adjusted so that the residual deviation on the cardinal headings is small. Why is the residual deviation recorded on a deviation card rather than eliminated completely?

  1. Because soft-iron effects cannot be corrected at all
  2. Because deviation varies with heading and a single setting cannot cancel it on every course Correct answer.
  3. Because corrector magnets cannot be adjusted finely enough to remove all deviation
  4. Because the card is required by regulation even when deviation is zero

Explanation

Deviation is a function of heading, so corrector magnets adjusted to minimise error on one set of headings leave some residual error elsewhere. The deviation card records the remaining error for each heading so the navigator can apply it. Complete elimination on all courses is not achievable with fixed correctors, and the card is a practical record rather than a regulatory formality.

Question 37Nautical instruments and their principles of operation

A vessel's magnetic compass is mounted close to a large loudspeaker magnet. What effect is most likely, and how should it be treated?

  1. No effect, because the compass is shielded by its bowl
  2. A temporary deviation that disappears when the loudspeaker is switched off
  3. An increase in directive force that improves compass stability
  4. A permanent deviation that should be removed by relocating the source or by compass adjustment Correct answer.

Explanation

A nearby permanent magnet produces a steady magnetic field at the compass, causing a deviation that persists while the source remains in place. The correct remedy is to remove or relocate the source and then swing the compass, because corrector magnets cannot reliably compensate a field that changes with the source's position. The bowl does not shield the compass from such a field.

Question 38Nautical instruments and their principles of operation

Which statement best describes the function of a fluxgate compass in a modern integrated bridge system?

  1. It senses the Earth's rotation to provide a true north reference
  2. It measures the Earth's magnetic field components electronically to derive heading Correct answer.
  3. It provides a backup depth reading for the echo sounder
  4. It measures the vessel's speed through the water for the log display

Explanation

A fluxgate compass uses saturable-core sensors to measure the horizontal components of the Earth's magnetic field and computes heading from them. It is a magnetic device and therefore needs deviation correction, unlike a gyrocompass, which senses Earth rotation. It does not measure speed or depth.

Question 39Nautical instruments and their principles of operation

A vessel's gyrocompass repeater shows a heading that differs from the master compass by a constant few degrees. Which cause is most likely?

  1. The repeater has not been synchronised with the master compass Correct answer.
  2. The latitude correction has been set incorrectly
  3. The speed error correction has been set to zero
  4. The master compass has lost its north-seeking ability

Explanation

Repeaters are synchro or step motors that must be aligned with the master compass; if a repeater is out of step, it shows a constant offset. A master compass fault or a correction error would affect the master heading itself and usually all repeaters together. Synchronising the repeater is therefore the first check for a constant single-repeater discrepancy.

Question 40Nautical instruments and their principles of operation

In a magnetic compass installation, what is the purpose of the quadrantal spheres?

  1. To indicate the lubber line for steering
  2. To damp the card's oscillation in heavy weather
  3. To correct semicircular deviation caused by permanent magnetism
  4. To correct quadrantal deviation caused by soft-iron effects Correct answer.

Explanation

Soft-iron spheres are placed on the binnacle to create a field that opposes the quadrantal deviation produced by the ship's induced magnetism, which varies with twice the heading angle. Semicircular deviation is corrected by permanent magnets, while damping and the lubber line are separate features. The spheres therefore address the quadrantal component specifically.

Question 41Magnetic and gyroscopic compasses

On a magnetic compass, what is the purpose of the liquid filling the bowl?

  1. It magnetises the needles and increases directive force
  2. It eliminates deviation caused by the ship's iron
  3. It replaces the need for a binnacle correction device
  4. It dampens oscillation of the card and supports most of the card's weight Correct answer.

Explanation

The liquid (typically a refined petroleum or alcohol mixture) provides buoyancy that relieves load on the pivot and viscous damping that calms card oscillation, so the compass settles quickly and steadies in a seaway. It has no magnetic function and cannot remove deviation.

Question 42Magnetic and gyroscopic compasses

The directive force acting on a magnetic compass needle is best described as:

  1. The total strength of the Earth's magnetic field
  2. The horizontal component of the Earth's magnetic field Correct answer.
  3. The vertical component of the Earth's magnetic field
  4. The magnetic moment of the compass needles

Explanation

Only the horizontal component of the geomagnetic field produces a turning moment that aligns the needle with magnetic north. The vertical component contributes nothing to horizontal alignment, and the needle's own magnetic moment is a property of the instrument, not a force from the field.

Question 43Magnetic and gyroscopic compasses

What is variation (magnetic declination)?

  1. The angle between the compass north and magnetic north
  2. The angle between magnetic north and true north at a given place Correct answer.
  3. The error introduced by the ship's permanent magnetism
  4. The tilt of the compass card caused by heeling

Explanation

Variation is the angular difference between the direction of the Earth's magnetic field (magnetic north) and the geographic meridian (true north) at the observer's position. It is a property of location and changes slowly with time.

Question 44Magnetic and gyroscopic compasses

Deviation of a magnetic compass is caused by:

  1. The magnetic field of the vessel and its equipment Correct answer.
  2. The difference between magnetic and true north
  3. The dip of the compass card in high latitudes
  4. The Earth's horizontal field changing with latitude

Explanation

Deviation is the angle between compass north and magnetic north and arises from the vessel's own magnetism, including permanent (hard-iron) and induced (soft-iron) fields. It varies with heading and changes when the ship's magnetic signature changes.

Question 45Magnetic and gyroscopic compasses

In a gyrocompass, the north-seeking property depends primarily on:

  1. The combination of gyroscopic inertia and the Earth's rotation Correct answer.
  2. The liquid damping applied to the sensitive element
  3. The magnetic field of the Earth acting on the rotor
  4. The spin speed of the rotor alone

Explanation

A gyrocompass uses a rapidly spinning rotor whose angular momentum resists change, together with gravity or a controlled torque that converts the Earth's rotation into a precession aligning the spin axis with true north. It is entirely independent of magnetism.

Question 46Magnetic and gyroscopic compasses

Which statement correctly distinguishes a magnetic compass from a gyrocompass?

  1. The magnetic compass indicates true north, while the gyrocompass indicates magnetic north
  2. The gyrocompass requires magnetic variation to be applied before use
  3. Both instruments indicate magnetic north but differ only in settling time
  4. The magnetic compass indicates magnetic north, while the gyrocompass settles on true north Correct answer.

Explanation

A magnetic compass aligns with the local magnetic field, giving magnetic north, so variation must be applied to obtain true bearings. A properly settled gyrocompass indicates true north and needs no variation correction, although it has its own residual errors.

Question 47Magnetic and gyroscopic compasses

What is the function of the Flinders bar in a magnetic compass binnacle?

  1. To damp the card's oscillation in heavy weather
  2. To correct quadrantal deviation arising from the vertical component of the ship's induced magnetism Correct answer.
  3. To hold the deviation table and sighting vanes
  4. To correct semicircular deviation caused by permanent magnetism

Explanation

The Flinders bar is a soft-iron corrector placed forward or aft of the compass to compensate for the induced magnetism of vertical soft iron in the ship, which produces quadrantal-type errors that change with latitude and heading. It does not address permanent-magnet semicircular deviation.

Question 48Magnetic and gyroscopic compasses

A vessel's gyrocompass is switched on in a new latitude after a long passage. Which behaviour is expected?

  1. The compass will settle instantly because the rotor speed is constant
  2. The compass will settle to the meridian after an oscillation period that depends on latitude Correct answer.
  3. The compass will require the Flinders bar to be re-adjusted
  4. The compass will indicate magnetic north until corrected by the officer on watch

Explanation

A gyrocompass settles by oscillating about the meridian with a period that lengthens as latitude increases, so it must be given time to settle after being started or after large latitude changes. Rotor speed is constant, but the settling dynamics are governed by latitude.

Question 49Magnetic and gyroscopic compasses

A magnetic compass reading is 045°C, the deviation from the table for that heading is 3°E, and variation is 5°W. What is the true bearing?

  1. 053°T
  2. 037°T
  3. 043°T Correct answer.
  4. 047°T

Explanation

The rule is: compass to true, add easterly and subtract westerly errors. Deviation of 3°E is added (045 + 3 = 048°M) and variation of 5°W is subtracted (048 − 5 = 043°T).

Question 50Magnetic and gyroscopic compasses

A true bearing of 200°T is to be converted to a compass bearing. Variation is 4°E and deviation for the approximate heading is 6°W. What compass bearing should be steered?

  1. 210°C
  2. 202°C Correct answer.
  3. 198°C
  4. 190°C

Explanation

Going from true to compass, westerly errors are added and easterly errors subtracted. Subtract 4°E (200 − 4 = 196°M), then add 6°W (196 + 6 = 202°C).