Auxiliary Engine / Generator — Most Asked Questions
24 questions asked about auxiliary engine / generator across the General and Fn 4b and Fn 3 and Fn 5 papers, heaviest first. 1 of them are must-master.
Learn the system first
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1 Emergency generator regulation
Also asked: “Emergency generator regulation full in detail”
Answer
SOLAS demands a fully independent emergency generator that starts itself within 45 seconds, from above the uppermost deck, outside the engine room.
- SOLAS Chapter II-1 Regulations 42 (passenger) and 43 (cargo) require a self-contained emergency generator.
- Location: above the uppermost continuous deck, outside the engine room, reachable from open deck, aft of the collision bulkhead, in the same compartment as the emergency switchboard.
- Performance: automatic start on loss of main power, on load within 45 seconds; starts at 0°C or has heating; runs at 22.5° list and stated trim.
- Fuel flash point not below 43°C; at least two independent starting sources, each good for three consecutive starts.
Surveyor follow-up: emergency generator starts but the emergency switchboard stays dead — name the two places you check first.
Full theory: Emergency Generator: Testing & Requirements -
2 MSB to Alternator safety
Answer
Between alternator and board stand interlocks, breakers and reverse-power trips: synchronise right or trip fast.
- Synchronise on voltage, frequency and phase before closing — dark lamps or a failed synchroscope means wait.
- Breaker interlocks stop paralleling a dead set onto a live board or closing out of phase.
- Reverse-power relay trips a motoring set before it drags the board and wrecks the prime mover.
- Prove protection on schedule: overcurrent, reverse power and preferential trips tested together.
Surveyor follow-up: breaker closes with lamps still rotating — what happens next, and which protection acts first?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
3 Alternator maintenance?
Also asked: “maintainance on alternator”
Answer
Alternator maintenance is clean, gap, brushes, AVR and bearings: ventilate, megger, measure and lubricate on schedule.
- Lock out, post notices and isolate the heater; clean ventilation passages, filters and windings with vacuum, never steel tools.
- Megger stator and rotor windings and log the trend; dry below 90 degrees if readings sag.
- Air gap 1.5–2 mm all round with a plastic feeler; slip rings true, brushes free with spring pressure proved.
- AVR cleaned of oil and dust, pedestal oil renewed, terminal gaskets and connections proved tight and dry.
Surveyor follow-up: air gap tight one side with normal megger — run, realign or renew bearings?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
4 Solas requirements for emergency generator
Also asked: “Emergency power source requirements in SOLAS”
Answer
The emergency set lives above the uppermost deck outside the engine room and takes load inside 45 seconds on blackout.
- SOLAS II-1 rules for passenger and cargo ships demand a self-contained set sized to the ship.
- Sited above the uppermost continuous deck, reachable from open deck, abaft the collision bulkhead with its own switchboard.
- Fuel flash point 43 degrees and up; auto-start to rated load inside 45 seconds with heating or easy cold start.
- Proved by blackout trials with bus-tie opening and batteries carrying lights meanwhile.
Surveyor follow-up: set starts but the board stays dead — bus-tie, breaker or AVR, and where first?
Full theory: Emergency Generator: Testing & Requirements -
5 Alternator air gap? Why is maintained?
Answer
The air gap is held 1.5–2 mm all round: tight for efficiency, even for balance, proved with a plastic feeler.
- Small gap cuts leakage flux and winding losses; wide gap wastes excitation and heat.
- Even gap all round avoids magnetic pull, vibration and rotor-to-stator rub under thermal and centrifugal load.
- Checked manually with a plastic feeler — never steel — and logged as bearing-health evidence.
- Doubles as cooling passage, so blocked ventilation plus a wide gap cooks the machine twice.
Surveyor follow-up: gap tight one side with normal megger — bearing, foundation or rotor, and what else do you measure?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
6 It is planned to carry top overhaul of Auxiliary engines, spell out the procedure of removal of cylinder cover and overhaul of safety valve/ indicator valve assembly, naming the parts with a simple sketch
Answer
Top overhaul lifts the cover, then proves the valves: isolate, lift to blocks, strip, lap, test and rebuild to sketch.
- Isolate fuel, air and cooling with starting air locked and turning gear engaged before a bolt moves.
- Lift the cover dead slow to wooden blocks with gasket faces protected and parts laid in order.
- Strip safety and indicator valves — springs, spindles and seats lapped, packed and bench-tested to lift.
- Sketch every part in removal order with torques and clearances; prove on turning gear before firing.
Surveyor follow-up: safety valve weeps on test after rebuild — lap, spring or seat, and what proves it?
Full theory: The Diesel Generator Set — Bedding Down, Coupling and Driving the Alternator -
7 alternator safeties?
Answer
Alternator safeties guard windings, excitation and board: overcurrent, reverse power and undervoltage with clean air and tight terminals.
- Overcurrent, reverse-power and undervoltage trips with preferential stages behind them.
- AVR, diodes, slip rings and brushes kept oil-free with air gaps and insulation proved.
- Ventilation passages vacuumed, terminal gaskets watertight, heaters and connections proved.
- Prove reverse-power with a deliberate motoring test — a protection never tried is a rumour.
Surveyor follow-up: motoring set with the relay silent — protection, wiring or settings, and what first?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
8 alternator overload protection
Also asked: “Motor overload protection”
Answer
Alternators shed load before they trip: preference relays drop hotel load near 110%, breakers guard faults above.
- Overload from switchboard growth or distribution faults meets inverse-time delay — brief motor starts ride through.
- Preference trips near 110% shed fans, air conditioning and galley in timed stages to save essential circuits.
- Short-circuit or sustained fault past settings opens the alternator breaker to protect windings.
- Prove by staged preference-trip test with seconds logged — unfired relays fail the blackout drill.
Surveyor follow-up: blackout with preferentials unfired and breakers intact — relay, settings or wiring first?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
9 Describe the process of replacing the cylinder liner in an auxiliary engine. How is water tightness ensured and what precautions are taken before commissioning the engine?
Answer
Renew AE liners clean and centred: lift the head, pull the liner, dress seats, renew O-rings, prove tightness before firing.
- Lift head and piston clear, pull the liner with its seals, and clean block seats to bright metal.
- Fit new sealing rings on cleaned lands with correct lubricant and lower the liner square without rolling the rings.
- Prove water tightness by jacket pressure test with the head off, watching lands and telltales for weeps.
- Commission by measuring piston-to-liner clearances at four points and several crank angles, bedding rings on light load with new-ring precautions.
Surveyor follow-up: jacket weeping past new O-rings with seats proved clean — rings, liner seating or block crack first?
Full theory: The Moving Parts — Liner, Piston, Gudgeon Pin and Connecting Rod Wear -
10 Make a report to the Chief Engineer of yourvessel about malfunctioning of low lub oil pressure alarm for the auxiliary engine, observed during your watch, with special emphasis on the possible consequences
Answer
Report the dead LO alarm as a protection failure: bellows, linkage, contacts and relay proved, with seizure the price of silence.
- Bellows expand and contract with pressure, driving contacts through a link into an amplified relay for alarm or shutdown.
- Spring setting trims the trip point — prove it lifting and resetting against a calibrated gauge, not by finger.
- A dead alarm lets bearings wipe, crank seize and the set black out the board without a whisper of warning.
- Repairs run clean contacts, free linkage, proven bellows and relay test logged with the chief’s signature before load returns.
Surveyor follow-up: alarm tested healthy with the gauge reading low and steady — instrument, pressure or pump first?
Full theory: Cooling, Lubrication and Fuel — Systems and the Tanks Checked Before Starting -
11 AVR working nd principle, alternator maintenance
Answer
The AVR holds voltage by changing rotor excitation: a shunt and series input added vectorially, feeding the field through the rectifier.
- Load current in the series coils adds input as load rises, so excitation increases and the voltage holds against the drop.
- A three-phase rectifier changes the AC to DC, which is smoothed and fed to the rotor through slip rings.
- Static AVR units trim out the small deviations from internal effects and load wander; error-operated units do it electromechanically.
- Maintenance is cleaning and adjustment: brushes and slip rings, the air gap, the sensing and control settings, and a load test.
Surveyor follow-up: voltage hunting on load with slip rings clean and gaps correct — is the sensing, the field or the load at fault?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
12 Auxiliary engine specs
Answer
Quote your ship’s own auxiliaries as four-stroke medium-speed sets: maker, bore and stroke, speed, rating and fuel.
- State the type and maker first — a four-stroke medium-speed diesel driving an alternator on the emergency or service bus.
- Give bore, stroke, number of cylinders and rated speed, so the surveyor can place it in the speed and duty class.
- Quote the rating in kW or hp, the fuel burnt and whether the rating is continuous or at 85% load for the engine.
- Add the alternator rating in kVA, voltage and frequency, and the duty hours it runs in a day — that is your ship’s answer, not a type.
Surveyor follow-up: engine and alternator ratings quoted with mismatched voltage — which one is wrong, and what does the board see?
Full theory: What the Auxiliary Engine Is — Why It Is a Four-Stroke Medium-Speed Machine -
13 Auxiliary engine trips
Answer
Auxiliary trips are the last line: low oil pressure, high temperature, overspeed and reverse power shut the set before damage.
- Alternator bearing low oil level and high temperature, plus low sump oil level, alarm and trip together.
- Lube oil low pressure alarms and trips, and jacket cooling water low pressure alarms protect the cooling circuit.
- Reverse current, overspeed and overload trips protect the set electrically; high and low frequency trips protect the grid.
- Every trip is proved on the routine — an untested trip is a protection that exists only on the drawing.
Surveyor follow-up: engine tripped on overspeed and the governor proved healthy — is the trip setting or the feedback pickup at fault?
Full theory: Governing and Speed Control — Droop, Load Sharing and the Overspeed Trip -
14 Brushless alternator regarding
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15 Describe how crankshaft deflections of an Auxiliary Engines are measured. ie (b) State how the measurements can be checked for accuracy. ( 4 (c) Specify with reasons other checks that should be made on the crankshaft. (5
Answer
Deflection is read with a dial gauge at each main bearing, and the readings are plotted as a curve to show sag, bend or twist.
- Set a dial gauge on each bearing and turn the engine over slowly, recording the reading at the crank throws and mid-stroke.
- Plot the readings with bearing 1 datum and positive above, negative below, so any bend shows as a curve off the line.
- Check the accuracy by repeating the run and confirming the readings repeat, and by checking the gauge zero between throws.
- Also check for ovality on the crankpins, the deflection curve against the maker’s limit, the oil holes for blockage, and the coupling alignment.
Surveyor follow-up: deflection curve within limits but one crankpin oval to twice the figure — does the curve catch that?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
16 Describe with the aid of a simple sketch the arrangement of the three phase winding of an alternator showing the neutral point. (6) (b) Explain why for most ships the neutral point is insulated. (5) (c) Explain why in so
Also asked: “Describe with the aid of a simple sketch the arrangement of the three phase winding of an alternator showing the neutral point. (6) (b) Explain why for most ships the neutral point is insulated. (5) (c) Explain why in some installation the neutral point is Earthed. (5”
Answer
Three phase windings join into a neutral in star; on most ships that neutral is insulated so a single earth fault does not trip the board.
- In star, the starting or finishing ends of the three coils are joined to form the neutral point, and the neutral wire is taken from it.
- That gives a three-phase four-wire system; delta joins opposite ends and gives three-phase three-wire with no neutral point.
- Most ships run three-phase three-wire with the alternator neutral points insulated, rather than the earthed systems used ashore.
- On a high-voltage system the neutral is earthed through a resistor instead, so the earth fault current is limited but not zero.
Surveyor follow-up: LV board with an earthed neutral where the survey called for insulated — which convention does that follow?
Full theory: Transformers, Diodes & Thyristors -
17 How do you take out main bearing of auxiliary engine
Answer
Out the same way as any main bearing: lift the cap, bridge-gauge the clearance, jack the shaft, and land the shell clear.
- Remove the lube oil supply to the bearing and keep the wear in order so the shell goes back to its own side.
- Lift the cap off with its eye bolts, seat the bridge gauge and feeler the journal gap on both sides.
- Jack the shaft on the webs to the maker’s limit, never more, then roll the bottom shell clear without levering it.
- With the shell out, inspect the crankpin for grooving and check the housing for wipe before refitting the cap.
Surveyor follow-up: shell marked and refitted to the wrong journal — which side is wrong, and what does the gauge show?
Full theory: Crankshaft Alignment, Web Deflections & Bearing Clearances -
18 If an auxiliary diesel generator over speedsand runs away while off load, explain: (a) How it can be stopped?
Answer
An overspeed with the breaker open means the governor did not act: stop it by killing fuel, locally if the remote stop is not provided.
- The sequence matters — the breaker tripped, the generator went suddenly off load, the governor failed to act and the rack stayed where it was.
- With the fuel rack unchanged the engine ran away, and the overspeed trip should have been the next thing to save it.
- Stop it by remote shutdown from the control room if that is provided, otherwise pull the fuel rack manually to the zero position.
- If it is considered unsafe to approach the machine, close the fuel supply valve at the fuel line or from outside the space instead.
Surveyor follow-up: runaway stopped by hand with the governor and trip both failed — is the machine safe to restart?
Full theory: Governing and Speed Control — Droop, Load Sharing and the Overspeed Trip -
19 Is auxiliary engine has tie rod or not?
Answer
No — auxiliaries carry no tie rods. They are small enough for bedplate and frame stiffness to hold the entablature unaided.
- Tie rods bind bedplate, A-frames and entablature in pre-stress because main-engine gas loads are enormous.
- An auxiliary engine is small enough that the bedplate and the block itself carry the firing loads.
- A four-stroke auxiliary also has an exhaust valve driven through the gear, with no long column to pull apart.
- Saying yes is the classic oral error — if the question names a two-stroke, the answer is the opposite.
Surveyor follow-up: auxiliary quoted with two long tie rods through the casing — designer’s choice, or the answer is wrong?
Full theory: What the Auxiliary Engine Is — Why It Is a Four-Stroke Medium-Speed Machine -
20 List the parts of an alternator fitted with temperature alarms. (6) (b) Explain why heaters are fitted to an Alternator. (6) (c) Explain the function of an automatic voltage regulator. (4
Answer
Temperature detectors watch the windings, bearings and cooling air; heaters stop condensation; the AVR holds the voltage by trimming field current.
- Detectors are resistance, thermistor or thermocouple types on the stator windings, the bearings and the cooling air and water.
- Single or grouped temperature alarms come to the main watchkeeping position, with a further alarm and a machine shutdown level.
- Heaters are fitted because a stopped alternator generates no heat, and moisture condenses on the windings and drops the insulation resistance.
- The AVR corrects the terminal voltage by changing the rotor excitation through the rectifier, with the series and shunt inputs adding vectorially.
Surveyor follow-up: alternator wound insulation low after a lay-up with the heaters proved dead — moisture, voltage or contamination?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
21 Special air cooled diesel generator. Ss
Answer
An air-cooled generator breathes through itself: fins, ducting and a fan, with the enclosures sealed and filtered against salt dust.
- Air-cooled machines have fins on the frame and windings, with cooling air drawn through by a fan on the rotor or a separate blower.
- Forced air in a closed circuit is pressurised through ventilation ducts in the stator core, between the rotor poles and across the air gap.
- Large machines may use water-cooled circulating air instead, and the air cooler keeps that closed circuit clean.
- The special points are the air filter condition, the fan bearing and the cooler — which is why air-cooled sets run hotter in salt air.
Surveyor follow-up: generator tripping on high winding temperature with clean filters and a sound fan — is the cooler, the duct or the load?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant -
22 Specification of alternator
Also asked: “Specifications of generator”
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23 Where Does the Emergency Generator Supply Goes?
Answer
The emergency generator feeds the emergency switchboard, and from there only the services that must survive a blackout.
- It supplies the emergency switchboard, which then feeds emergency lighting, steering gear circuits and navigation.
- Communications, the alarm and monitoring systems, and the emergency fire pump take their power from that same board.
- It does not feed the main switchboard, and it is not a spare for the service generators — it is the blackout supply.
- It is tested under load, not just run: a loaded test is what proves the emergency board really comes alive.
Surveyor follow-up: emergency generator started monthly but never on load — which part of the supply is still unproved?
Full theory: The Emergency Generator — Location, Starting, Fuel and the Emergency Board -
24 Why Alternator rating is in KVA and motor in KW, what is Power factor..??
Answer
A generator is rated in kVA because its windings carry a fixed current at a fixed voltage whatever the load does to the power factor.
- The power delivered, √3·V·I·cos φ, depends on the load power factor, so the true kW is not known until the load is connected.
- Conductors are sized for a definite current and the insulation and magnetic system for a definite voltage, both independent of power factor.
- So apparent power in kVA is treated as the rated power of the alternator, and the power factor is specified alongside it.
- The same is true of transformers, UPS and motors; kW is the output the load actually takes.
Surveyor follow-up: alternator rated 400 kVA at 0.8 pf — how many kW is that, and who decides the pf?
Full theory: The Alternator and Switchboard — AVR, Load Shedding and the Automatic Plant
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.