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BD Marine Engineer Class 4 (Coastal CE) study materials
BD Marine Engineer Class 4 (Coastal CE) study resources

BD Marine Engineer Class 4 (Coastal CE) practice questions

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Question 1Marine Propulsion Machinery and Power Plants

In a four-stroke marine diesel engine, which valve is normally open during the intake stroke?

  1. Exhaust valve
  2. Inlet valve Correct answer.
  3. Neither valve
  4. Both inlet and exhaust valves

Explanation

The intake stroke draws fresh charge or air into the cylinder, so the inlet valve must be open while the piston travels down the cylinder. The exhaust valve stays closed during this stroke to prevent the charge escaping through the exhaust passage. Valve timing is arranged so the inlet opens slightly before top dead centre and closes after bottom dead centre to improve filling.

Question 2Marine Propulsion Machinery and Power Plants

What is the primary function of the scavenging process in a two-stroke marine diesel engine?

  1. To remove exhaust gas and refill the cylinder with fresh air Correct answer.
  2. To cool the piston crown directly
  3. To lubricate the cylinder liner
  4. To increase the compression ratio

Explanation

Scavenging replaces burnt gases remaining in the cylinder with fresh air so that the next compression stroke starts with a clean, air-filled cylinder. Efficient scavenging raises the trapped air mass and therefore the fuel that can be burnt. It is driven by a blower or by the pressure difference between the scavenge receiver and the exhaust system.

Question 3Marine Propulsion Machinery and Power Plants

Which component converts the reciprocating motion of the piston into rotary motion of the crankshaft?

  1. Camshaft
  2. Flywheel
  3. Cylinder liner
  4. Connecting rod Correct answer.

Explanation

The connecting rod links the piston to the crankpin and, as the piston reciprocates, it swings to turn the crankshaft. Its big-end and small-end bearings allow this angular movement under heavy gas and inertia loads. The other listed parts perform different roles in the running gear and valve train.

Question 4Marine Propulsion Machinery and Power Plants

In a medium-speed diesel engine, what is the main purpose of the turbocharger?

  1. To drive the camshaft
  2. To reduce torsional vibration
  3. To cool the lubricating oil
  4. To increase the mass of air trapped in the cylinder Correct answer.

Explanation

A turbocharger uses exhaust gas energy to drive a compressor that delivers air at higher density, so more air mass enters the cylinder. This allows more fuel to be burnt per cycle and raises power output for a given engine size. Charge air is usually cooled after compression to further increase density.

Question 5Marine Propulsion Machinery and Power Plants

Which fuel property most directly indicates the ease with which a diesel fuel ignites under compression?

  1. Viscosity
  2. Cetane number Correct answer.
  3. Flash point
  4. Sulphur content

Explanation

The cetane number is a measure of ignition quality: a high cetane number means short ignition delay and smoother combustion. It is determined in a standard test engine by comparison with reference fuels. Viscosity, sulphur and flash point describe other handling and safety characteristics.

Question 6Marine Propulsion Machinery and Power Plants

What is the function of the air receiver in a compressed-air starting system?

  1. To store air at working pressure for engine starting Correct answer.
  2. To filter oil from the compressed air
  3. To reduce the air delivery temperature
  4. To regulate the fuel rack position

Explanation

The air receiver stores a reserve of compressed air so that the engine can be started repeatedly without the compressor running continuously. It also damps pressure pulsations from the compressor. Stored pressure is maintained within limits and protected by relief and drain arrangements.

Question 7Marine Propulsion Machinery and Power Plants

Which type of pump is most commonly used for main engine cylinder cooling water circulation on smaller coastal vessels?

  1. Reciprocating positive displacement pump
  2. Jet pump
  3. Centrifugal pump Correct answer.
  4. Rotary gear pump

Explanation

Centrifugal pumps are preferred for large cooling water flows because they give high capacity at moderate head with few wearing parts. They run continuously and are self-regulating to some extent against a throttled discharge. Positive displacement pumps are used where high pressure and precise flow are required.

Question 8Marine Propulsion Machinery and Power Plants

What does the term 'dead centre' refer to in a reciprocating engine?

  1. The position of the piston at the extreme ends of its stroke Correct answer.
  2. The midpoint of the cylinder liner
  3. The point where the crankshaft is stationary during normal running
  4. The point of maximum combustion pressure

Explanation

Top and bottom dead centre are the extreme piston positions where the crank and connecting rod are in line and piston velocity is momentarily zero. Valve timing and fuel injection timing are commonly referenced to these positions. They are geometric reference points, not a normal running stop.

Question 9Marine Propulsion Machinery and Power Plants

A four-stroke engine has a bore of 300 mm and a stroke of 450 mm. Using pi = 3.142, what is the swept volume of one cylinder in litres?

  1. 42.4 litres
  2. 15.9 litres
  3. 10.6 litres
  4. 31.8 litres Correct answer.

Explanation

Swept volume equals cylinder area times stroke. Area is pi times radius squared, with radius 0.15 m, giving about 0.0707 square metres; multiplying by 0.45 m stroke gives about 0.0318 cubic metres, or 31.8 litres. Care must be taken to use radius, not diameter, in the area calculation.

Question 10Marine Propulsion Machinery and Power Plants

During a compression test on a diesel engine, one cylinder reads noticeably lower than the others. Which cause is most consistent with this result?

  1. Late fuel injection timing on that cylinder
  2. Worn piston rings or a leaking exhaust valve Correct answer.
  3. Incorrect governor droop setting
  4. A blocked fuel injector nozzle

Explanation

Low compression pressure indicates leakage from the combustion space or reduced clearance volume, which is typically caused by worn rings, scored liners or poorly seating valves. Fuel and governor faults affect combustion but do not lower the measured compression pressure. Confirming with a leak-down test helps localise the leakage path.

Question 11Marine Propulsion Machinery and Power Plants

Why is charge air cooled after the turbocharger compressor on a marine diesel engine?

  1. To increase the density of air entering the cylinder Correct answer.
  2. To prevent the compressor from surging
  3. To reduce the lubricating oil consumption
  4. To lower the exhaust gas temperature only

Explanation

Cooling the compressed charge increases its density, so a greater mass of air is trapped in the cylinder for the same swept volume. This permits more fuel to be burnt and reduces thermal loading and NOx formation. The cooler also protects the engine from excessively hot intake air.

Question 12Marine Propulsion Machinery and Power Plants

What is the main consequence of excessive ignition delay in a large diesel engine?

  1. A rapid pressure rise causing mechanical and thermal stress Correct answer.
  2. Reduced peak pressure and smoother running
  3. Lower exhaust gas temperature
  4. Increased scavenge air pressure

Explanation

When ignition delay is long, a large quantity of fuel accumulates before ignition, and it then burns rapidly, producing a steep rate of pressure rise. This causes high peak pressures and shock loading on bearings, pistons and cylinder heads. Correct fuel quality, injection timing and atomisation keep delay within design limits.

Question 13Marine Propulsion Machinery and Power Plants

A main engine governor is set to constant-speed mode. What does this mean in practice?

  1. The engine runs at a fixed speed regardless of load up to its limit Correct answer.
  2. The engine speed falls in direct proportion to load
  3. The fuel rack is held at a fixed position
  4. The engine stops automatically at rated load

Explanation

In constant-speed or isochronous control the governor adjusts fuel delivery to hold the set speed as load changes, within the engine's capability. This is essential where frequency must be stable, such as when driving an alternator. Proportional droop control, by contrast, allows speed to fall with load.

Question 14Marine Propulsion Machinery and Power Plants

Why must the lubricating oil for a trunk-piston medium-speed engine be kept alkaline?

  1. To improve its viscosity index
  2. To reduce foaming in the sump
  3. To increase its flash point
  4. To neutralise acidic combustion products and prevent corrosion Correct answer.

Explanation

Combustion of sulphur-bearing fuel forms acidic products that can condense on liners and bearings. An alkaline reserve in the oil neutralises these acids and protects bearing and liner surfaces from corrosion. The reserve is monitored by base number testing and replenished by oil changes or top-up.

Question 15Marine Propulsion Machinery and Power Plants

In a crosshead two-stroke engine, why is a separate cylinder lubricating system used instead of relying on crankcase oil?

  1. To prevent acidic combustion residues from contaminating the crankcase oil Correct answer.
  2. Because crankcase oil is too viscous for bearings
  3. To reduce the quantity of oil used in the bearings
  4. Because cylinder oil is cheaper than crankcase oil

Explanation

The crosshead and diaphragm separate the combustion space from the crankcase, so cylinder oil can be total-loss and formulated to handle acidic residues. This arrangement keeps abrasive and acidic products out of the crankcase oil used for bearings. It also allows the cylinder oil feed to be matched to load and sulphur level.

Question 16Marine Propulsion Machinery and Power Plants

What is the purpose of the turning gear on a large marine diesel engine?

  1. To rotate the engine slowly for maintenance and to prevent shaft distortion Correct answer.
  2. To start the engine with compressed air
  3. To drive the attached pumps
  4. To increase the engine speed during manoeuvring

Explanation

The turning gear rotates the crankshaft slowly by an electric motor so that pistons, liners and bearings can be inspected and serviced. It is also used to turn the engine periodically when stopped hot, preventing uneven cooling and shaft sag. It must be interlocked so the engine cannot be started while engaged.

Question 17Marine Propulsion Machinery and Power Plants

A ship's main engine shows a rising exhaust gas temperature on one unit while all other parameters remain normal. Which action is the most appropriate first step?

  1. Increase the fuel index to compensate
  2. Reduce speed and investigate that unit's fuel injection and exhaust valve Correct answer.
  3. Change the turbocharger bearings
  4. Ignore it until the next scheduled overhaul

Explanation

A single-unit temperature deviation points to a local fault such as a faulty injector, valve leakage or scavenge problem in that unit. Reducing load protects the affected components while the cause is investigated. Increasing fuel would worsen the condition and could lead to damage.

Question 18Marine Propulsion Machinery and Power Plants

What is the function of a fuel injection pump's delivery valve in a jerk-type system?

  1. To cool the injector nozzle
  2. To maintain residual pressure in the high-pressure line and prevent backflow Correct answer.
  3. To filter abrasive particles from the fuel
  4. To vary the engine speed

Explanation

The delivery valve opens to admit high-pressure fuel to the line and closes to isolate the pump, with a relief action that drops line pressure sharply to ensure rapid injector closing. It also retains a residual pressure to keep the line primed and prevent backflow. This gives clean injection cut-off and avoids secondary injection.

Question 19Marine Propulsion Machinery and Power Plants

Which statement best describes the role of a thrust bearing on a marine propulsion shafting system?

  1. It aligns the intermediate shaft to the gearbox
  2. It seals the shaft where it passes through the hull
  3. It transmits the propeller thrust to the ship's hull Correct answer.
  4. It supports the weight of the propeller shaft

Explanation

The thrust bearing takes the axial force generated by the propeller and transfers it to the hull structure so the ship moves. Without it, the thrust would load the gearbox or engine bearings. Radial loads are carried by separate line bearings.

Question 20Marine Propulsion Machinery and Power Plants

What is the main reason for fitting a torsional vibration damper on a medium-speed engine crankshaft?

  1. To reduce the amplitude of torsional oscillations at critical speeds Correct answer.
  2. To balance the reciprocating mass of the pistons
  3. To absorb axial thrust from the propeller
  4. To increase the engine's compression ratio

Explanation

Torsional dampers add damping at the crankshaft front end to limit the amplitude of torsional oscillations when the engine passes through, or runs near, a critical speed. Excessive torsional vibration can cause crankshaft or coupling failure. They do not balance reciprocating masses or carry thrust.

Question 21Marine Propulsion Machinery and Power Plants

A main engine fails to start on compressed air although the air receiver pressure is normal. Which fault is most likely?

  1. The fuel oil viscosity is too low
  2. The lubricating oil level is too high
  3. The starting air distributor is out of timing Correct answer.
  4. The sea water temperature is too low

Explanation

The starting air distributor admits air to each cylinder in the correct firing order at the proper crank angle; if it is mistimed, air may be admitted at the wrong piston position and the engine will not turn. Other checks include the main starting valve and manoeuvring linkage. Fuel and cooling conditions do not prevent the engine turning on air.

Question 22Marine Propulsion Machinery and Power Plants

During manoeuvring, a two-stroke engine must be capable of running astern. How is this normally achieved on a direct-coupled reversible engine?

  1. By changing the camshaft and starting air timing to run the engine in reverse Correct answer.
  2. By using a reversing gearbox on the shaft
  3. By reversing the propeller pitch only
  4. By reversing the direction of the turbocharger

Explanation

A reversible direct-coupled engine reverses by shifting the camshaft or by using reversing servos so that fuel injection and starting air timing suit the opposite direction of rotation. Starting air is then admitted to turn the engine astern. There is no gearbox in a direct-coupled arrangement and the turbocharger direction is not reversed.

Question 23Marine Propulsion Machinery and Power Plants

An engine indicator diagram shows combustion pressure peaking well after top dead centre and exhaust temperature is high. What does this suggest?

  1. The compression ratio is too high
  2. Injection timing is too retarded Correct answer.
  3. Injection timing is too advanced
  4. The scavenge air is too cold

Explanation

Late injection delays combustion, so peak pressure occurs further down the expansion stroke and more heat passes to the exhaust. The remedy is to check and correct injection timing and pump settings. Advanced timing would instead give an early, high peak pressure.

Question 24Marine Propulsion Machinery and Power Plants

Why is a diaphragm fitted between the scavenge space and the crankcase of a crosshead two-stroke engine?

  1. To increase the scavenge air pressure
  2. To support the crosshead guides
  3. To cool the piston rod
  4. To prevent oil mist and air from passing between the two spaces Correct answer.

Explanation

The diaphragm separates the under-piston scavenge space from the crankcase so that air and oil mist cannot migrate between them. This protects crankcase oil from contamination and prevents scavenge air loss. It also reduces the risk of a crankcase mist explosion being fed by scavenge air.

Question 25Marine Propulsion Machinery and Power Plants

A turbocharged engine suffers a sudden loss of scavenge air pressure with a rise in exhaust temperature after the turbocharger. Which combination of causes best fits these symptoms?

  1. A worn fuel injector nozzle
  2. A blocked lubricating oil filter
  3. A fouled compressor or a leaking charge air cooler Correct answer.
  4. An incorrectly set governor droop

Explanation

Reduced compressor efficiency, from fouling or air-side leakage, lowers the delivered air pressure and mass flow, so less air is available and exhaust temperature rises. A leaking or fouled charge air cooler can produce a similar pressure loss. Injector, governor and lube oil faults do not cause a general scavenge pressure loss.

Question 26Marine Propulsion Machinery and Power Plants

In a four-stroke marine diesel engine, which valve arrangement is typical of a modern uniflow-scavenged design?

  1. Two inlet valves in the cylinder head and two exhaust valves in the cylinder head
  2. One inlet valve in the cylinder head and exhaust ports in the cylinder liner
  3. Exhaust valves in the cylinder head and scavenge air ports in the cylinder liner Correct answer.
  4. Inlet and exhaust ports both located in the cylinder liner

Explanation

Four-stroke engines normally use poppet valves in the cylinder head for both inlet and exhaust, but the uniflow arrangement described here refers to the common practice of head-mounted exhaust valves with liner air ports used in some opposed-piston and large two-stroke-derived designs; for a four-stroke trunk engine the standard is head valves for both. Candidates should identify the arrangement where exhaust leaves through a head valve while air enters through liner ports as the uniflow ported type.

Question 27Marine Propulsion Machinery and Power Plants

What is the primary purpose of the scavenge air receiver on a uniflow-scavenged two-stroke engine?

  1. To house the turbocharger bearings and cooling water
  2. To store fuel for injection during manoeuvring
  3. To damp torsional vibration in the crankshaft
  4. To provide a steady supply of air at slightly above atmospheric pressure to the cylinder liner ports Correct answer.

Explanation

The scavenge air receiver acts as a reservoir that smooths pressure pulsations from the turbocharger and delivers a steady flow of air to the scavenge ports. Maintaining a slight positive pressure relative to the exhaust ensures the cylinder is cleared of burnt gases before compression begins.

Question 28Marine Propulsion Machinery and Power Plants

A medium-speed trunk engine has a fuel injection pump with a helix-controlled plunger. What does rotating the plunger within its barrel achieve?

  1. It sets the opening pressure of the injector needle
  2. It changes the effective stroke and therefore the quantity of fuel delivered Correct answer.
  3. It alters the injection timing only, without affecting quantity
  4. It controls the cooling water flow to the injector

Explanation

In a helix-controlled jerk pump, rotating the plunger aligns the helical groove with the spill port at a different point in the stroke. This varies the effective pumping stroke and hence the fuel quantity delivered per stroke.

Question 29Marine Propulsion Machinery and Power Plants

Why is a relief valve fitted to the crankcase of a large marine diesel engine?

  1. To allow lubricating oil to be drained quickly during a change
  2. To prevent dangerous overpressure of the crankcase in the event of a crankcase explosion Correct answer.
  3. To supply additional air to the turbocharger during acceleration
  4. To maintain a positive pressure in the crankcase for oil return

Explanation

A crankcase relief valve opens at a set low pressure to vent gases and prevent the crankcase from rupturing if an oil mist ignites. It is a safety device required by classification societies on engines above a certain power.

Question 30Marine Propulsion Machinery and Power Plants

A two-stroke engine is running with a scavenge air pressure of 1.4 bar gauge and an exhaust gas temperature after the turbocharger of 380 °C. Which condition is most consistent with these readings?

  1. The turbocharger is fouled and needs water washing
  2. The engine is operating normally at a moderate load Correct answer.
  3. The fuel injection timing is retarded
  4. The scavenge air cooler is bypassed

Explanation

A scavenge pressure of about 1.4 bar gauge together with an exhaust temperature near 380 °C after the turbine is typical of a healthy turbocharged two-stroke at moderate load. Fouled turbochargers, retarded timing, or a bypassed cooler would each shift these values in characteristic directions.

Question 31Marine Propulsion Machinery and Power Plants

During a routine check, the lubricating oil sample from a medium-speed engine shows a sudden rise in water content and a drop in viscosity. Which action is most appropriate?

  1. Add fresh oil to dilute the water and continue running
  2. Reduce the engine load and ignore the reading
  3. Investigate for a leaking cooler or cylinder liner and treat the oil Correct answer.
  4. Increase the oil change interval to compensate

Explanation

A sudden rise in water content together with a fall in viscosity indicates contamination, commonly from a leaking cooler or a failed liner seal. The source must be found and the oil purified or replaced before bearing damage occurs.

Question 32Marine Propulsion Machinery and Power Plants

What is the function of the air cooler condensate drain in the charge air system?

  1. To drain fuel from the injector leak-off line
  2. To remove water that condenses from the cooled charge air before it enters the cylinder Correct answer.
  3. To vent excess air from the receiver during starting
  4. To supply cooling water to the turbocharger bearings

Explanation

Cooling the compressed charge air causes water vapour to condense, and the drain removes this condensate so that it does not enter the cylinder and cause corrosion or water hammer. Regular draining is part of routine engine room practice.

Question 33Marine Propulsion Machinery and Power Plants

A main engine governor is switched from constant-speed to droop mode for parallel operation with a shaft generator. What is the practical effect of this change?

  1. The engine maintains exactly the same speed regardless of load
  2. The engine speed falls as load increases, allowing load sharing between generators Correct answer.
  3. The engine speed rises as load increases
  4. The governor disables fuel injection during overload

Explanation

Droop control allows speed to decrease slightly as load increases, which provides the feedback needed to share load between paralleled generators. Without droop, small speed errors cause large circulating currents between machines.

Question 34Marine Propulsion Machinery and Power Plants

Why is a starting air interlock fitted between the turning gear and the starting air system?

  1. To increase the air pressure available for reversing
  2. To prevent starting air being admitted while the turning gear is engaged Correct answer.
  3. To allow the engine to be turned while starting air is admitted
  4. To reduce the starting air consumption during manoeuvring

Explanation

The interlock ensures that starting air cannot be admitted to the cylinders while the turning gear is still engaged, which would cause catastrophic damage. The engine cannot be started until the turning gear is fully disengaged.

Question 35Marine Propulsion Machinery and Power Plants

On a crosshead two-stroke engine, what is the primary reason for maintaining a slight negative pressure in the crankcase relative to the scavenge space?

  1. To improve lubrication of the crosshead guides
  2. To increase the charge air pressure entering the cylinder
  3. To prevent oil mist and vapours from escaping into the engine room and to keep scavenge air out of the crankcase Correct answer.
  4. To assist the piston cooling oil return

Explanation

Maintaining the crankcase slightly below scavenge pressure, together with the diaphragm, keeps oil mist from escaping and prevents scavenge air from blowing into the crankcase. This protects both personnel and lubricating oil quality.

Question 36Marine Propulsion Machinery and Power Plants

During manoeuvring, a direct-coupled two-stroke engine must reverse quickly. Which feature allows the camshaft to be repositioned for astern running?

  1. A reversing servomotor that shifts the camshaft or cam followers Correct answer.
  2. A reversal of the cooling water flow through the cylinder jackets
  3. A change in the fuel injection pump plunger helix angle
  4. A change in the direction of rotation of the turbocharger

Explanation

In a direct-reversing engine, the camshaft or its followers are shifted by a servomotor so that the valve and fuel pump cams act at the correct timing for the opposite direction of rotation. The crankshaft itself simply reverses direction under starting air.

Question 37Marine Propulsion Machinery and Power Plants

An engine indicator diagram shows a combustion pressure peak that is lower than normal and occurs late, while exhaust temperature is high. Which fault best explains this?

  1. Excessive fuel injection quantity
  2. A leaking exhaust valve seat
  3. Late or faulty fuel injection Correct answer.
  4. Excessive scavenge air pressure

Explanation

Late injection delays combustion, so the peak pressure is lower and occurs later in the expansion stroke, while unburnt fuel continues to burn and raises exhaust temperature. The combination points to injection timing or injector condition rather than to air supply.

Question 38Marine Propulsion Machinery and Power Plants

A four-stroke auxiliary engine has a compression ratio of 14:1 and a swept volume of 12 litres. What is the approximate clearance volume?

  1. 0.86 litre
  2. 0.92 litre Correct answer.
  3. 0.75 litre
  4. 1.20 litre

Explanation

Compression ratio equals (swept volume plus clearance volume) divided by clearance volume. Rearranging gives clearance volume equal to swept volume divided by (compression ratio minus one), so 12 divided by 13 equals approximately 0.92 litre.

Question 39Marine Propulsion Machinery and Power Plants

A turbocharged engine shows a gradual rise in exhaust temperature and a fall in scavenge air pressure over several weeks, with no change in fuel rack position. Which combination of causes is most likely?

  1. A failed starting air valve
  2. Fouled turbocharger compressor and turbine, or a fouled charge air cooler Correct answer.
  3. A worn fuel injection pump plunger
  4. A blocked lubricating oil filter

Explanation

Progressive fouling of the compressor reduces air delivery while turbine fouling reduces turbocharger efficiency, both lowering scavenge pressure and raising exhaust temperature. A fouled charge air cooler has a similar effect by raising charge air temperature.

Question 40Marine Propulsion Machinery and Power Plants

In a trunk-piston medium-speed engine, why is the lubricating oil specified with a higher base number than that used in a crosshead two-stroke engine?

  1. Because trunk engines run at higher speeds and need thicker oil
  2. Because crosshead engines do not use lubricating oil
  3. Because trunk engines have no oil filters
  4. Because trunk engines burn more sulphur-rich fuel and the oil must neutralise acidic combustion products in the same circuit Correct answer.

Explanation

In a trunk engine the same oil lubricates the bearings and the cylinder liner, so it must neutralise acidic products from sulphur in the fuel. Crosshead engines use a separate cylinder oil with a high base number and keep crankcase oil separate from combustion products.

Question 41Auxiliary Machinery and Shipboard Systems

On a coastal vessel, which device prevents the main air compressor from restarting automatically after an overload trip until the fault is acknowledged and reset?

  1. The air receiver safety valve
  2. The motor starter overload relay with manual reset Correct answer.
  3. The compressor unloading valve solenoid
  4. The automatic start/stop pressure switch

Explanation

An overload relay with manual reset latches out after a trip so the motor cannot restart until the operator investigates and resets it. The pressure switch only controls starting and stopping within the set pressure band, and the unloading solenoid and safety valve are not part of the electrical protection circuit.

Question 42Auxiliary Machinery and Shipboard Systems

A centrifugal pump on a coastal vessel is running but delivering almost no water, and the discharge pressure gauge reads low. Which cause is most consistent with these symptoms?

  1. The discharge non-return valve is fully open
  2. The discharge valve is throttled too far open
  3. The suction strainer is blocked, causing cavitation Correct answer.
  4. The mechanical seal is leaking slightly to drain

Explanation

A blocked suction strainer starves the impeller, so flow falls and the pump runs in cavitation with low discharge pressure. A slightly leaking seal causes only minor seepage, a fully open non-return valve supports normal flow, and throttling would normally raise rather than lower the discharge head.

Question 43Auxiliary Machinery and Shipboard Systems

What is the primary purpose of fitting a salinity cell in the distillate outlet line of a ship's evaporator?

  1. To detect salt carry-over and divert off-specification distillate Correct answer.
  2. To control the heating steam pressure
  3. To indicate the vacuum in the evaporator shell
  4. To measure the density of the feed water

Explanation

The salinity cell monitors the conductivity of the produced distillate and, through its controller, diverts the flow to drain when the salt content exceeds the set limit. This protects the ship's fresh water system from contamination caused by priming or carry-over.

Question 44Auxiliary Machinery and Shipboard Systems

During routine operation of a marine oil-fired auxiliary boiler, the burner trips repeatedly and the flame scanner shows a weak signal. Which action is the correct first response?

  1. Increase the fuel oil pressure to strengthen the flame
  2. Bypass the flame failure protection to keep steam available
  3. Isolate the burner, investigate and clean the scanner and flame detector Correct answer.
  4. Reduce the combustion air to stabilise the flame

Explanation

A weak flame signal indicates a dirty or misaligned scanner, so the burner must be stopped and the detector cleaned and checked before further running. Flame failure protection must never be bypassed, and altering fuel or air settings without diagnosis risks a furnace explosion.

Question 45Auxiliary Machinery and Shipboard Systems

Which statement correctly describes the action of the purifier (centrifugal separator) bowl when separating water from fuel oil?

  1. The water phase collects at the centre and is removed by the feed pump
  2. The heavier water phase moves outward to the bowl wall and is discharged through the water outlet Correct answer.
  3. Both phases leave through the clean oil outlet together
  4. The lighter oil phase moves outward and is discharged through the sludge port

Explanation

In a disc-stack purifier the denser water is thrown to the outer periphery and leaves through the adjustable water outlet, while the lighter cleaned oil flows inward to the oil outlet. Correct gravity disc selection keeps the interface in the right position for efficient separation.

Question 46Auxiliary Machinery and Shipboard Systems

A steering gear hydraulic system is fitted with two independent power units. What is the main reason for this arrangement?

  1. To reduce the size of the hydraulic reservoir
  2. To permit manual hand pumping during normal running
  3. To allow higher rudder speed in port
  4. To provide redundancy so steering remains available after a single failure Correct answer.

Explanation

Duplicated power units give redundancy so that loss of one pump or its supply does not leave the vessel without steering. Regulations require steering capability to be maintained after a single failure in the steering system.

Question 47Auxiliary Machinery and Shipboard Systems

Which parameter is normally used to trigger the automatic changeover from the duty to the standby generator in a ship's electrical plant?

  1. An increase in the alternator excitation current
  2. A rise in the main switchboard room temperature
  3. A drop in generator winding temperature
  4. A fall in busbar frequency or a loss of the running generator Correct answer.

Explanation

Automatic changeover is initiated by a detected abnormality such as loss of the running generator, low frequency or low voltage on the busbar. The standby set then starts and is synchronised to restore supply.

Question 48Auxiliary Machinery and Shipboard Systems

What is the function of the air vessel fitted on the discharge side of a reciprocating bilge or general service pump?

  1. To prevent the pump from running backwards
  2. To measure the quantity of liquid delivered
  3. To smooth the pulsating flow and reduce pressure fluctuation Correct answer.
  4. To filter solid matter from the pumped liquid

Explanation

A reciprocating pump delivers in pulses, and the air vessel acts as a cushion that absorbs and releases energy to give a steadier discharge. This reduces pressure surges and water hammer in the discharge line.

Question 49Auxiliary Machinery and Shipboard Systems

A shell-and-tube lube oil cooler shows rising oil outlet temperature with normal cooling water flow. Which fault is the most likely cause?

  1. The oil temperature control valve is fully closed
  2. The cooling water inlet valve is fully open
  3. The tube bundle is fouled on the water side Correct answer.
  4. The oil pump is running at reduced speed

Explanation

Fouling on the water side adds thermal resistance, so heat transfer falls and the oil leaves hotter for the same water flow. Reduced oil pump speed would lower heat input, and a closed control valve would bypass the cooler rather than cause this pattern.

Question 50Auxiliary Machinery and Shipboard Systems

Which safety device on a marine auxiliary boiler prevents the furnace from being flooded with fuel after a flame failure?

  1. The steam pressure relief valve
  2. The flame failure trip acting on the fuel oil shut-off valve Correct answer.
  3. The feed water regulator
  4. The water level gauge glass

Explanation

On flame failure the flame failure trip closes the fuel oil shut-off valve and stops the burner, preventing unburnt fuel accumulating in the furnace. This interlock is a key protection against furnace explosion.