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OBC Detection, Lighting & Power practice questions

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Question 1Outboard Detection Systems: Sensors and Coverage

Which sensor type is most commonly used to detect a target's distance by measuring the time delay of a returning acoustic pulse?

  1. Active sonar transducer Correct answer.
  2. Electro-optical infrared camera
  3. Passive hydrophone array
  4. Magnetic anomaly detector

Explanation

Active sonar emits an acoustic pulse and measures the two-way travel time to derive range from the known speed of sound in water. Passive sensors only listen and cannot directly measure range this way. Magnetic and electro-optical sensors respond to different physical signatures entirely.

Question 2Outboard Detection Systems: Sensors and Coverage

What does the detection range of a passive acoustic sensor primarily depend on?

  1. The color temperature of the target's exhaust plume
  2. Target source level, propagation loss, and ambient noise level Correct answer.
  3. The transmit power of the sensor's own projector
  4. The rotation rate of the sensor platform

Explanation

Passive detection depends on how loud the target is, how much energy is lost along the propagation path, and how much background noise masks the signal. Because the sensor does not transmit, its own projector power is irrelevant. Platform rotation and plume color do not govern acoustic detection range.

Question 3Outboard Detection Systems: Sensors and Coverage

A hull-mounted sonar dome is designed primarily to do which of the following?

  1. Amplify the acoustic signal before transmission
  2. Protect the transducer while allowing acoustic energy to pass Correct answer.
  3. Convert acoustic energy into electrical power
  4. Block all acoustic noise from the ship's machinery

Explanation

The dome is an acoustic window that shields the transducer from flow, debris, and pressure while remaining transparent to sound. It is not an amplifier or a power generator. It may reduce some self-noise but is not designed to block all machinery noise.

Question 4Outboard Detection Systems: Sensors and Coverage

Which phenomenon most directly limits active sonar performance in shallow coastal water?

  1. Reduced speed of sound in fresh water
  2. Complete loss of the transducer's electrical power
  3. Absence of any acoustic propagation
  4. Increased reverberation from bottom and surface boundaries Correct answer.

Explanation

In shallow water, sound reflects repeatedly off the bottom and surface, creating reverberation that masks weak target echoes. Propagation still occurs, and sound speed changes are modest. Power loss is an equipment fault, not an environmental limitation.

Question 5Outboard Detection Systems: Sensors and Coverage

What is the primary function of a magnetic anomaly detector (MAD) in outboard detection?

  1. To sense localized disturbances in the Earth's magnetic field caused by a ferrous target Correct answer.
  2. To detect the thermal wake left by a surface vessel
  3. To determine target range by timing a returned pulse
  4. To measure the acoustic signature of a target's propeller

Explanation

A MAD senses the small distortion a ferrous hull imposes on the ambient geomagnetic field. It does not rely on acoustics, thermal signatures, or pulse timing. Its detection range is short, which is why it is often used for localization rather than broad search.

Question 6Outboard Detection Systems: Sensors and Coverage

Which factor most strongly determines the acoustic coverage footprint of a towed array?

  1. Array length, operating frequency, and tow depth Correct answer.
  2. The color of the tow cable jacket
  3. The number of crew assigned to the sonar watch
  4. The fuel type used by the towing vessel

Explanation

Coverage depends on aperture length, frequency-dependent beam patterns, and depth relative to sound-speed profiles. Cable color, crew count, and fuel type do not affect acoustic geometry. Longer arrays and lower frequencies generally yield narrower beams and greater detection range.

Question 7Outboard Detection Systems: Sensors and Coverage

What does the term 'bearing' mean in the context of a passive sonar contact?

  1. The speed of the target relative to the sensor
  2. The horizontal angle from the sensor to the target Correct answer.
  3. The distance from the sensor to the target
  4. The vertical depth of the target below the sensor

Explanation

Bearing is an angular measurement in the horizontal plane, indicating the direction of the contact relative to a reference. Depth is a vertical measure, range is distance, and speed is a rate. Passive systems often provide bearing without immediate range.

Question 8Outboard Detection Systems: Sensors and Coverage

Why is a convergence zone useful to a sonar operator?

  1. It eliminates all ambient noise in the water column
  2. It creates a region of enhanced detection at long range due to sound refraction Correct answer.
  3. It prevents sound from bending near the surface
  4. It converts acoustic energy into magnetic energy

Explanation

Refraction in the deep ocean can focus sound into annular zones at long range, producing detectable levels far beyond direct-path range. Convergence zones do not remove ambient noise, stop refraction, or change energy type. Operators exploit these zones to extend search coverage.

Question 9Outboard Detection Systems: Sensors and Coverage

An operator receives a passive bearing with no range information. Which additional sensor or method could provide a range estimate?

  1. Repeating the same bearing measurement from the same array
  2. Lowering the system's audio volume
  3. Increasing the display brightness
  4. Triangulating bearings from a second spatially separated array Correct answer.

Explanation

Two bearings taken from widely separated positions intersect at the target, yielding a range fix by triangulation. Display brightness and audio volume do not add information. Repeating a measurement from the same location gives no new geometric constraint.

Question 10Outboard Detection Systems: Sensors and Coverage

A target's broadband acoustic signature is strongest at high frequencies, but the operator needs long-range detection. What trade-off applies?

  1. Lower frequencies propagate farther but require larger apertures for comparable resolution Correct answer.
  2. Broadband signatures cannot be detected passively
  3. Higher frequencies always give both better range and better resolution
  4. Frequency has no effect on propagation loss

Explanation

Absorption loss increases with frequency, so lower frequencies travel farther in water. However, lower frequencies have longer wavelengths that demand larger apertures to achieve a given angular resolution. No single frequency optimizes both range and resolution simultaneously.

Question 11Outboard Detection Systems: Sensors and Coverage

A surface ship operating its own active sonar experiences strong returns from the sea surface directly above the target. What is this effect called?

  1. Convergence
  2. Cavitation
  3. Surface reverberation Correct answer.
  4. Doppler shift

Explanation

Reverberation is the scattering of transmitted energy by boundaries and volume inhomogeneities, and surface returns are a form of it. Convergence refers to refocused long-range sound, cavitation is bubble formation, and Doppler shift is a frequency change from relative motion.

Question 12Outboard Detection Systems: Sensors and Coverage

Why does a sonar operator prefer a narrow horizontal beam when searching near a loud interferer?

  1. It eliminates the need for a display
  2. It reduces the angular sector from which interfering energy is received Correct answer.
  3. It increases the speed of sound in the local water
  4. It lowers the target's source level

Explanation

A narrow beam concentrates sensitivity in a small sector, so noise arriving from other directions is attenuated relative to the target direction. Beamwidth does not alter sound speed, remove the display, or change the target's emitted level. This spatial filtering is a core advantage of aperture and frequency design.

Question 13Outboard Detection Systems: Sensors and Coverage

A MAD-equipped aircraft flies a straight survey line. What detection geometry does this produce?

  1. A narrow swath along the flight path where field disturbance exceeds threshold Correct answer.
  2. A cone that widens only behind the aircraft
  3. A vertical cylinder extending to the seafloor
  4. A full 360-degree circle of equal sensitivity

Explanation

MAD sensitivity falls off rapidly with lateral distance from the sensor, so the effective search area is a narrow swath beneath and near the flight path. Coverage is not uniform in all directions and does not extend as a full cylinder or trailing cone. This is why MAD is used for localization after other sensors cue it.

Question 14Outboard Detection Systems: Sensors and Coverage

What is the main purpose of a sound velocity profile in sonar coverage planning?

  1. To predict how refraction will bend sound rays and shape detection zones Correct answer.
  2. To measure the electrical conductivity of seawater
  3. To set the brightness of the operator display
  4. To determine the target's magnetic signature

Explanation

The sound velocity profile describes how speed changes with depth, which controls ray bending and thus shadow zones and convergence zones. Conductivity, magnetic signature, and display settings are unrelated. Accurate profiles let planners predict where detection is enhanced or degraded.

Question 15Outboard Detection Systems: Sensors and Coverage

Two passive arrays separated by a known baseline each report a bearing to the same contact. The bearings cross at a shallow angle. What is the effect on range accuracy?

  1. Range accuracy improves because the geometry is more stable
  2. Range error grows because small bearing errors translate into large range errors at shallow crossing angles Correct answer.
  3. Range error is unaffected by the crossing angle
  4. Range becomes independent of bearing accuracy

Explanation

In triangulation, the position uncertainty is governed by the crossing angle; near-parallel bearings produce large range uncertainty for a given bearing error. A wide crossing angle gives a more robust fix. Thus shallow-angle geometry degrades range accuracy rather than improving it.

Question 16Outboard Detection Systems: Sensors and Coverage

Which environmental condition most increases self-noise received by a hull-mounted passive sonar?

  1. Reduced salinity of the local water
  2. Rough sea state and increased own-ship speed Correct answer.
  3. A colder target exhaust plume
  4. A perfectly calm sea with the ship stopped

Explanation

Flow noise, wave slap, and machinery noise all rise with sea state and speed, degrading the signal-to-noise ratio for a hull-mounted passive sensor. Calm conditions and low speed reduce self-noise. Salinity and plume temperature do not drive self-noise.

Question 17Outboard Detection Systems: Sensors and Coverage

A narrowband tonal at a fixed frequency is detected. What does the presence of a stable tonal most likely indicate?

  1. Random ocean ambient noise
  2. A magnetic anomaly
  3. A rotating or reciprocating machinery source on the target Correct answer.
  4. A thermal plume boundary

Explanation

Stable narrowband tones typically arise from periodic machinery such as engines, pumps, or shaft lines. Ambient noise is broadband and random, while magnetic and thermal phenomena are not acoustic tones. Tonals are valuable classification cues for passive sonar.

Question 18Outboard Detection Systems: Sensors and Coverage

What does the detection threshold in a sonar equation represent?

  1. The minimum signal-to-noise ratio at which a contact is reliably declared Correct answer.
  2. The physical depth at which the array is towed
  3. The maximum power the transducer can transmit
  4. The angular width of the transmit beam

Explanation

Detection threshold is the required signal excess above background noise for a specified probability of detection and false alarm. It is not a power limit, tow depth, or beamwidth. Operators use it to judge whether a faint contact is credible.

Question 19Outboard Detection Systems: Sensors and Coverage

An active sonar transmits a pulse and receives an echo 4 seconds later. Assuming a sound speed of 1500 m/s, what is the approximate one-way range to the target?

  1. 3000 m Correct answer.
  2. 1500 m
  3. 750 m
  4. 6000 m

Explanation

The round-trip distance is 1500 m/s times 4 s, or 6000 m. The one-way range is half of that, giving 3000 m. Forgetting to halve the travel time is the most common error in this calculation.

Question 20Outboard Detection Systems: Sensors and Coverage

A target closing on a passive sensor emits a constant-frequency tone. How does the received frequency change?

  1. It drops to zero at closest approach
  2. It increases as the range decreases Correct answer.
  3. It remains exactly constant
  4. It decreases as the range decreases

Explanation

Doppler shift raises the received frequency when the source approaches and lowers it when it recedes. A constant emitted tone therefore appears higher in pitch during closure. The shift is proportional to closing speed relative to sound speed.

Question 21Outboard Detection Systems: Sensors and Coverage

A bi-static active sonar configuration uses a separate source and receiver. What coverage advantage can this provide?

  1. Detection only directly behind the source
  2. Elimination of the need for accurate timing
  3. Detection of targets that are not on the source-receiver line, using forward-scattered energy Correct answer.
  4. Complete immunity to reverberation

Explanation

Separating source and receiver allows the system to exploit forward-scatter geometry, illuminating targets outside the monostatic backscatter path. Reverberation is not eliminated, precise timing remains essential, and coverage is not limited to behind the source. This geometry can counter quiet targets that absorb rather than reflect.

Question 22Outboard Detection Systems: Sensors and Coverage

Why can a quiet diesel-electric submarine operating on battery be harder to detect passively than a surfaced vessel?

  1. It produces low radiated machinery and flow noise and presents a small acoustic cross-section Correct answer.
  2. Its propeller cavitates continuously at high speed
  3. It generates a large magnetic anomaly at long range
  4. It emits a strong broadband acoustic signature

Explanation

Submerged battery operation removes engine noise and reduces wake and flow noise, lowering radiated levels. A strong broadband signature, large long-range magnetic anomaly, and continuous cavitation would all make detection easier, not harder. Quieting measures aim to shrink the detectable signature.

Question 23Outboard Detection Systems: Sensors and Coverage

An operator observes a contact whose bearing rate decreases steadily toward zero while range remains large. What does this trend most likely indicate?

  1. The target has stopped all machinery
  2. The sensor array has failed
  3. The target is moving directly away at high speed
  4. The target is approaching a closest-point-of-approach geometry Correct answer.

Explanation

A decreasing bearing rate that trends toward zero is characteristic of a target nearing closest point of approach, where the line-of-sight angle changes slowest. A directly receding target would show a different range trend, array failure would remove the contact, and stopped machinery would eliminate the acoustic source.

Question 24Outboard Detection Systems: Sensors and Coverage

In a deep-ocean duct, sound is trapped near the axis of a sound channel. What is the primary consequence for detection?

  1. Low transmission loss along the duct allows long-range detection within the channel Correct answer.
  2. Detection is limited to the surface layer only
  3. The duct blocks all acoustic energy from entering
  4. Sound is absorbed completely within a few kilometers

Explanation

The sound channel refracts rays back toward the axis, confining energy and reducing spreading loss so contacts can be heard at long range. Energy is not fully absorbed, detection is not restricted to the surface, and the duct does not block entry. Understanding ducting helps operators predict extended coverage.

Question 25Outboard Detection Systems: Sensors and Coverage

A planner must choose between a high-frequency and a low-frequency active system for detecting a small target at long range in a noisy environment. Which reasoning is most sound?

  1. High frequency always wins because it improves both range and resolution
  2. Low frequency reduces absorption loss but may reduce resolution, so the choice depends on the required detection range versus classification detail Correct answer.
  3. Low frequency eliminates ambient noise entirely
  4. Frequency choice is irrelevant to detection performance

Explanation

Absorption loss rises with frequency, favoring lower frequencies for long range, but longer wavelengths reduce the ability to resolve small features. The correct choice balances required range against classification detail and noise conditions. No single frequency dominates both criteria, and ambient noise is never eliminated.

Question 26Outboard Detection Systems: Sensors and Coverage

Which sonar mode depends on a target reflecting acoustic energy that the target itself did not generate?

  1. Active sonar Correct answer.
  2. Wake-homing detection
  3. Passive sonar
  4. Magnetic anomaly detection

Explanation

Active sonar works by transmitting an acoustic pulse and listening for the echo returned from the target, so detection relies on reflected energy rather than energy radiated by the target. Passive systems only listen, while magnetic and wake-homing methods use non-acoustic signatures.

Question 27Outboard Detection Systems: Sensors and Coverage

What does the detection range of a passive sonar fundamentally depend on?

  1. The pulse length chosen by the operator
  2. The transmit power of the receiving platform
  3. The echo strength returned from the target
  4. The source level of the target and the ambient noise at the receiver Correct answer.

Explanation

A passive system emits nothing, so its detection range is set by how loud the target is at the relevant frequency and by how much noise competes with that signal at the receiver. Transmit power, pulse length and echo strength belong to active sonar.

Question 28Outboard Detection Systems: Sensors and Coverage

What is the primary function of a sonar dome or acoustic window on a hull-mounted transducer?

  1. To amplify incoming sound before it reaches the transducer
  2. To filter out all frequencies below the cavitation band
  3. To protect the transducer while allowing sound to pass through Correct answer.
  4. To generate the acoustic pulse used for ranging

Explanation

The dome is a structural cover that shields the transducer from water flow and pressure while remaining acoustically transparent at the operating band. It does not amplify, generate or selectively filter the signal in the way the other options describe.

Question 29Outboard Detection Systems: Sensors and Coverage

What does a sonar operator mean by the term 'port-starboard ambiguity'?

  1. A contact whose range exceeds the display scale
  2. A bearing that could lie on either side of the array axis Correct answer.
  3. A bearing that cannot be resolved into a frequency
  4. A contact that is masked by the ship's own wake

Explanation

A linear or towed array measures the angle of incoming sound relative to its own axis, and a cone of directions on one side mirrors a cone on the other. As a result a single measured angle corresponds to two possible bearings, one to port and one to starboard.

Question 30Outboard Detection Systems: Sensors and Coverage

Which sensor provides a non-acoustic means of detecting a submerged steel-hulled submarine from the air?

  1. A hull-mounted passive array
  2. A dipping sonar
  3. A sonobuoy
  4. A magnetic anomaly detector Correct answer.

Explanation

A magnetic anomaly detector senses the local distortion of the earth's magnetic field caused by a large ferrous mass such as a submarine hull. The other options are acoustic sensors that rely on sound rather than magnetic signature.

Question 31Outboard Detection Systems: Sensors and Coverage

What is the main reason a sonar operator plots successive bearings to a contact rather than relying on a single bearing?

  1. Successive bearings measure the target's radiated noise level
  2. A single bearing gives no range, but a sequence reveals target motion Correct answer.
  3. A single bearing is always inaccurate by several degrees
  4. Successive bearings eliminate the need for a sound velocity profile

Explanation

One bearing defines only a line of position, and the target could be anywhere along it. Plotting how the bearing changes over time allows the operator to infer course, and with own-ship manoeuvres, to estimate range by triangulation.

Question 32Outboard Detection Systems: Sensors and Coverage

A frigate tows a passive array at 12 knots in sea state 4. Which change would most improve detection of a quiet contact?

  1. Increasing own-ship speed to reduce flow noise
  2. Shortening the array to reduce handling loads
  3. Reducing own-ship speed to lower flow and machinery noise Correct answer.
  4. Raising the array closer to the surface

Explanation

Flow noise and radiated machinery noise from the towing platform rise with speed and can mask a quiet contact, so slowing down reduces the self-noise competing with the target. Surface proximity and a shorter array generally degrade passive performance rather than improve it.

Question 33Outboard Detection Systems: Sensors and Coverage

A narrowband analysis shows a steady tone at 50 Hz from a contact. Which interpretation is most reasonable?

  1. The contact is an active sonar transmission
  2. The contact is a passive sonar array
  3. The contact is a biological source such as a whale
  4. The contact is likely a machinery source such as a diesel generator Correct answer.

Explanation

Low-frequency steady tones are characteristic of rotating machinery and reciprocating engines, whose harmonics appear as stable narrowband lines. Active transmissions are broadband or frequency-modulated pulses rather than continuous steady tones.

Question 34Outboard Detection Systems: Sensors and Coverage

Two hull-mounted arrays on the same ship, separated by 30 m, each measure a bearing to a distant contact. What does comparing the two bearings allow?

  1. An estimate of target range by triangulation Correct answer.
  2. Elimination of all ambient noise
  3. Direct measurement of target depth
  4. Determination of target radiated frequency

Explanation

When two receivers at a known separation each provide a line of bearing to the same contact, the intersection of those lines fixes position, and the geometry yields range. The baseline is short, so the range estimate is coarse but still useful.

Question 35Outboard Detection Systems: Sensors and Coverage

An active sonar in shallow water is plagued by strong returns arriving shortly after transmission from the seabed and surface. What is the standard name for these returns?

  1. Cavitation
  2. Multipath fading
  3. Doppler shift
  4. Reverberation Correct answer.

Explanation

Reverberation is the unwanted scattering of the transmitted pulse from the seabed, sea surface and volume inhomogeneities, and it competes directly with the target echo. In shallow water with strong boundaries it often sets the practical detection limit.

Question 36Outboard Detection Systems: Sensors and Coverage

An operator wishes to detect a contact at long range in deep water using a passive towed array. Which frequency band should generally be exploited?

  1. The band where absorption is greatest
  2. Very high frequencies above 20 kHz
  3. Frequencies matching the array's structural resonance
  4. Low frequencies of a few hertz to a few hundred hertz Correct answer.

Explanation

Seawater absorption increases strongly with frequency, so low frequencies travel much farther and support long-range passive detection. High frequencies are useful for resolution and short-range work but are quickly attenuated.

Question 37Outboard Detection Systems: Sensors and Coverage

An operator must decide whether a faint contact is real or a random fluctuation. Which concept best describes the level the signal must exceed to be declared a detection?

  1. The source level
  2. The detection threshold Correct answer.
  3. The figure of merit of the projector
  4. The transmission loss

Explanation

The detection threshold expresses the signal-to-noise ratio required at the receiver to declare a detection for a chosen probability of detection and false alarm. It sits above the noise and is set by the operator or processor, not by the source or the medium.

Question 38Outboard Detection Systems: Sensors and Coverage

A target is receding directly away from a passive sensor and emits a constant 400 Hz tone. What does the sensor receive?

  1. A frequency slightly below 400 Hz Correct answer.
  2. A frequency that alternates above and below 400 Hz
  3. A frequency slightly above 400 Hz
  4. Exactly 400 Hz with no change

Explanation

Relative motion along the line of sight shifts the received frequency, and a receding target stretches the wavefronts so the received frequency falls below the emitted one. The effect is the acoustic equivalent of the Doppler shift.

Question 39Outboard Detection Systems: Sensors and Coverage

A bistatic active system places its receiver well away from the transmitter. What coverage benefit does this geometry offer?

  1. It eliminates reverberation from the seabed
  2. It allows detection of targets that are quiet in the monostatic direction Correct answer.
  3. It removes the need for a sound velocity profile
  4. It guarantees a longer pulse can be used

Explanation

With separated source and receiver, the detection opportunity occurs where the target scatters energy toward the receiver rather than back toward the source. A target presenting a low echo in the backscatter direction may still be detected through forward or side scatter.

Question 40Outboard Detection Systems: Sensors and Coverage

A planner wants a sensor that can detect a submarine without revealing the searching platform's presence. Which choice is consistent with that requirement?

  1. A high-power dipping sonar
  2. A passive towed array listening for radiated noise Correct answer.
  3. An active hull-mounted sonar transmitting continuously
  4. An active sonobuoy pinging on a fixed schedule

Explanation

A passive sensor emits no acoustic energy, so the searching platform does not announce itself and the target receives no warning of the search. Active systems broadcast their presence and can be detected at ranges well beyond their own detection range.

Question 41Outboard Detection Systems: Sensors and Coverage

An operator observes that a contact's bearing changes rapidly while its inferred range stays small. What does this most likely indicate?

  1. A stationary target at long range
  2. A false contact caused by reverberation
  3. A close target passing at high crossing speed Correct answer.
  4. A distant target on a steady bearing

Explanation

Bearing rate is greatest when a target is close and crossing the line of sight quickly, because the same linear motion subtends a larger angle at short range. A distant or stationary target produces a small or zero bearing rate.

Question 42Outboard Detection Systems: Sensors and Coverage

A survey aircraft flies a series of parallel straight lines over an area while towing a magnetic anomaly detector. What does this pattern primarily provide?

  1. A method of classifying target machinery tones
  2. A means of measuring target depth directly
  3. Continuous acoustic coverage of the whole area
  4. Systematic spatial coverage so that a magnetic anomaly is crossed Correct answer.

Explanation

A magnetic anomaly detector has a short effective range, so detection depends on the aircraft passing close to the target. Parallel track spacing is chosen so the surveyed lanes overlap in coverage and no gap allows a submarine to pass undetected.

Question 43Outboard Detection Systems: Sensors and Coverage

An active sonar operator needs the best possible bearing resolution against two close contacts. Which change supports that goal?

  1. Lowering the transmitted frequency and shortening the pulse
  2. Increasing the transmitted frequency and using a larger aperture Correct answer.
  3. Increasing the pulse repetition interval
  4. Reducing the receiver bandwidth

Explanation

Angular resolution improves with a larger aperture relative to wavelength, so a higher frequency and a bigger array both narrow the beam. Lower frequency or a smaller effective aperture widens the beam and blurs closely spaced contacts together.

Question 44Outboard Detection Systems: Sensors and Coverage

A passive sonar array uses two closely spaced elements to estimate the bearing of a contact. For a given signal-to-noise ratio, what happens to bearing accuracy as the separation between the two elements increases?

  1. Bearing accuracy is unchanged because only the signal-to-noise ratio sets the accuracy.
  2. Bearing accuracy degrades because the two elements begin to receive uncorrelated noise.
  3. Bearing accuracy improves because the phase difference between the elements grows larger for a given arrival angle. Correct answer.
  4. Bearing accuracy improves only if the operating frequency is also raised.

Explanation

Bearing accuracy depends on the phase or time-difference measurement across the array aperture. Widening the separation increases the phase difference produced by a given arrival angle, so a fixed phase-measurement error corresponds to a smaller bearing error. The gain is limited by spatial coherence of the signal and by the onset of ambiguity when separation approaches half a wavelength at the operating frequency.

Question 45Outboard Lighting Circuits and Luminaire Types

Which conductor colour typically identifies the negative return in a two-wire outboard navigation light circuit?

  1. Black Correct answer.
  2. Red
  3. Green
  4. Brown

Explanation

In common marine DC wiring conventions the negative return is black, while red carries the positive feed from the battery or distribution panel. Consistent colour coding lets a technician trace a fault without guessing polarity.

Question 46Outboard Lighting Circuits and Luminaire Types

A vessel's stern light must be visible over which arc of the horizon?

  1. 360 degrees
  2. 225 degrees
  3. 112.5 degrees
  4. 135 degrees Correct answer.

Explanation

The stern light shows over a 135-degree arc centred on the vessel's centreline aft, so it is visible from dead astern and 67.5 degrees to each side. Sidelights cover 112.5 degrees each, and the masthead light covers 225 degrees.

Question 47Outboard Lighting Circuits and Luminaire Types

What is the standard sector coverage of a single sidelight on a power-driven vessel?

  1. From dead ahead to 22.5 degrees abaft the beam Correct answer.
  2. From dead ahead to 45 degrees abaft the beam
  3. From dead astern to 22.5 degrees forward of the beam
  4. From the beam to dead astern

Explanation

Each sidelight shines from dead ahead to 22.5 degrees abaft the beam, giving a 112.5-degree arc. The red light sits to port and the green to starboard.

Question 48Outboard Lighting Circuits and Luminaire Types

Which luminaire type produces light by passing current through a gas-filled tube coated with phosphor?

  1. Incandescent
  2. LED
  3. Fluorescent Correct answer.
  4. Halogen

Explanation

Fluorescent luminaires excite mercury vapour in a tube, and the ultraviolet output is converted to visible light by a phosphor coating. LEDs use semiconductor junctions, while incandescent and halogen lamps use a heated filament.

Question 49Outboard Lighting Circuits and Luminaire Types

On a power-driven vessel underway at night, what colour is the masthead light?

  1. Yellow
  2. White Correct answer.
  3. Green
  4. Red

Explanation

Masthead lights are white and shine over a 225-degree arc from dead ahead to 22.5 degrees abaft each beam. Red and green are reserved for the port and starboard sidelights.

Question 50Outboard Lighting Circuits and Luminaire Types

Which material is commonly used as the filament in an incandescent marine lamp?

  1. Carbon steel
  2. Nichrome
  3. Copper
  4. Tungsten Correct answer.

Explanation

Tungsten has a very high melting point, allowing a filament to glow white-hot without failing quickly. Copper and steel would melt or oxidise at the temperatures needed for visible light.