Main Engine — Most Asked Questions
19 questions asked about main engine across the General and Fn 4b papers, heaviest first.
Learn the system first
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1 MAIN ENGINE SPECIFICATIONS
Also asked: “Main engine specs”
Answer
Quote the engine as numbers: bore, stroke, speed, output per cylinder and specific consumption — then total power.
- Bore and stroke in millimetres define each cylinder’s swept volume; square engines match the two.
- Rated speed in rpm with output per cylinder in kilowatts — multiply by cylinder count for MCR.
- Specific fuel consumption in grams per kilowatt-hour states her appetite at rating.
- Finish with mass and builder: a medium-speed six and twelve of one family weigh hundreds of tonnes apart.
Surveyor follow-up: two engines with equal bore but different stroke — which pulls harder at low rpm, and why?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
2 types of ME engine
Answer
Main engines are named by cycle, piston, speed and use: two-stroke crosshead slow-speed for propulsion, four-stroke trunk for the rest.
- Cycle first: two-stroke fires every revolution, four-stroke every second — ports versus valves tell them apart.
- Piston next: crosshead with guides for big two-strokes, trunk with skirts for four-strokes.
- Speed bands: low-speed 100 rpm and below for direct-drive propulsion, medium and high speed for geared and auxiliary duty.
- Cylinders 4 to 12 in line, V, W or X layouts for main propulsion or generator service.
Surveyor follow-up: name your last ship’s engine by all four — cycle, piston, speed and use.
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
3 Which turbocharger you have on Main engine?
Answer
Name your turbocharger by maker and frame: MAN, ABB or Mitsubishi matched to the engine for lowest fuel rate.
- MAN B&W low-speeds take MAN, ABB or Mitsubishi wheels chosen for best specific consumption at rating.
- Fewest wheels possible per engine with maker selection data behind the choice.
- State yours: maker, model, cylinders served and rated speed from the plate.
- Back it with upkeep: filter, cooler, bearings and surging history the surveyor will chase.
Surveyor follow-up: same engine with a different maker’s wheel — rating, matching or piping, and what changes?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
4 Engine output reduces because of low boost air pressure
Also asked: “• Engine output reduces because of low boost air pressure”
Answer
Low boost starves the fire: fouled gas and air paths choke the turbocharger and the engine cannot make power.
- Fouled turbine nozzles and blades clog exhaust flow and raise back pressure against scavenging.
- Oiled suction casing, diffuser and cooler fins plus clogged liner ports strangle the air side delivery.
- Charge pressure falls, exhaust temperature climbs, and fuel must be cut back to protect the engine.
- Recover by washing air and gas sides, proving coolers and filters, and trending boost against load.
Surveyor follow-up: boost low with exhaust temperature high and fuel already limited — wash, open up or slow down first?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
5 Main engine interlocks
Answer
Interlocks stop a start that would break the engine: turning gear out, control matched, air and valves proven.
- Turning gear disengaged and withdrawn before starting air can reach the distributor.
- Control lever, fuel and reversing positions proved matched so the engine cannot kick the wrong way.
- Starting-air pressure, control air, exhaust valves and slow-turn or blow-through proved before fuel admits.
- Any interlock outstanding blocks the start — bypassing one for a departure earns the surveyor’s hardest question.
Surveyor follow-up: bridge rings ahead with the turning gear still engaged — what should block the start?
Full theory: Starting the Engine — Air Start Valve, Distributor and the Four Interlocks -
6 Main engine nomenclature
Also asked: “Engine nomenclature in detail”
Answer
Read the engine name as data: maker, stroke, bore, cylinders and control concept are stamped in the designation.
- MAN B&W letters spell programme, stroke-to-bore family and control — camshaft or electronically controlled marks.
- Bore in centimetres with cylinder count and mark number give size and series at a glance.
- GI marks gas injection, compact or exhaust-valve-by-cam letters mark the concept — absent means fuel-oil only.
- Quote your last ship’s full designation and decode each group aloud before the surveyor asks.
Surveyor follow-up: decode 6S60ME-C on the spot — bore, strokes, control and cylinder count?
Full theory: Engine Nomenclature — Decode MAN, Sulzer, Daihatsu & Spec Sheets -
7 Main engine, aux engine difrence with specifications
Also asked: “Diff bw main and aux engine”, “Main engine and aux engine specs and nomenclature”
Answer
Main engines are slow two-stroke crossheads on heavy fuel; auxiliaries are medium-speed four-stroke trunks on cleaner fuel.
- Main engines complete the cycle in two strokes of a long-stroke crosshead, direct-driving the propeller at low revolutions.
- Auxiliaries complete it in four strokes of a trunk-piston medium-speed engine, usually geared or generating electric power.
- Two-stroke ports replace inlet valves with BDC suction; four-stroke valves open at TDC with higher speed and lower weight per kilowatt.
- Medium-speed mains exist but need gears and couplings — quote power, speed, bore and fuel for both on your ship.
Surveyor follow-up: why can a medium-speed main never bolt straight to the propeller like a slow-speed two-stroke?
Full theory: What the Auxiliary Engine Is — Why It Is a Four-Stroke Medium-Speed Machine -
8 Medium speed engines: ranging from 300 to 1000 rpm
Also asked: “• Medium speed engines: ranging from 300 to 1000 rpm”
Answer
Medium speed means hundreds of revolutions: roughly 300 to 1000 rpm in compact four-stroke trunk engines.
- Low-speed cathedral crossheads stay below about 240 rpm for direct propeller drive.
- Medium-speed trunk engines run the hundreds band, driving generators or propellers through gears.
- High-speed engines run past a thousand into small craft, emergency and fast auxiliary duty.
- Name speed by frequency too — revolutions per second — when the surveyor tests modern usage.
Surveyor follow-up: 720 rpm generator engine with a reduction gear to the shaft — slow, medium or high speed?
Full theory: Four-Stroke Aux Engines — Layout to Lubrication -
9 Speed – high speed, medium speed, slow speed
Also asked: “• Speed – high speed, medium speed, slow speed”
Answer
Speed classes split the fleet: slow direct-drive giants, medium geared workhorses, high-speed compact sets.
- Slow-speed two-stroke crossheads turn below about 240 rpm and bolt to the shaft.
- Medium-speed four-strokes run the hundreds to 1000 rpm through gears or alternators.
- High-speed engines run beyond into compact, light, fast-response duty with shorter overhaul lives.
- Bore alone never decides the class — speed, stroke, drive and duty do.
Surveyor follow-up: 260 mm bore turning 900 rpm — slow or medium, and what gives it away?
Full theory: Four-Stroke Aux Engines — Layout to Lubrication -
10 The following will be required to be done in order to reduce sulphur corrosion of main Engine Components
Answer
Beat sulphur corrosion with heat, alkalinity and cleanliness: burn right, neutralise acids, drain water.
- Keep liner and head temperatures above the acid dew point so sulphuric condensate cannot settle.
- Match alkaline cylinder oil base number to fuel sulphur and feed it correctly at load.
- Purify bunkers hard, drain settling and service tanks, and strip catalytic fines that grind liners bare.
- Trend liner wear by calibration — rising wear with low-sulphur fuel means over-alkaline oil, not safety.
Surveyor follow-up: liner wear rising after a low-sulphur stem with full alkaline feed — more oil, less base, or hotter jackets?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
11 Main engine trips?
Answer
Main-engine trips stop fuel before damage spreads: overspeed, lost oil or water, hot bearings, mist and scavenge fire.
- Overspeed and crankcase oil-mist trips kill fuel instantly — the two explosions no engineer outruns.
- Low lube-oil, low jacket-water and high piston-cooling temperatures trip before seizure and cracking.
- Hot thrust pads, hot exhaust units and high stern-tube temperatures join the trip chain at load.
- Prove by trip-test log with sensors lifted: an untested trip is a rumour, not a protection.
Surveyor follow-up: trip alarm muted with the sensor proved faulty at sea — bypass, slow down or stop, and who signs?
Full theory: Two-Stroke Main Engine Standby & Start Preparation: Preheating, Turning Gear, Blow-Through & Bridge Control Changeover -
12 Briefly explain the following; (i) How would you know a Refrigeration System is Undercharged? (4) (ii) What should you do to ensure that there is no Water Leakage into the Engine Cylinder before preparing Main Engine for
Also asked: “Briefly explain the following; (i) How would you know a Refrigeration System is Undercharged? (4) (ii) What should you do to ensure that there is no Water Leakage into the Engine Cylinder before preparing Main Engine for Sea? (6) (in en would cause the Level of the Lub Oil Sump of Main Engine or Drain Tank to ise?”
Answer
An undercharged system runs starved, and a cylinder about to start must be proved dry by turning it over and checking the drains.
- Signs of undercharge: the compressor runs hot on high superheat, suction and discharge pressures are low, and the ammeter reads low.
- The liquid sight glass shows large vapour bubbles, the condenser gauges read low, the room warms, and the compressor runs for long periods.
- Before preparing the engine, turn it over completely and check that all water is drained away from the cylinders.
- Verify the cooling water system is filled and vented, and confirm the crankcase and drains are clear before the first fuel is admitted.
Surveyor follow-up: a cylinder wet at the drain after barring — drain, dry the charge, or is that a head or liner leak?
Full theory: Refrigeration Principles and the Vapour Compression Cycle -
13 Main engine indicator cock leaking. Actions
Answer
A weeping indicator cock is exhaust gas into the engine room: cap it, and renew it at the next shutdown.
- Check the cock is not leaking exhaust gas — that is a standing watchkeeping duty, not a defect note.
- Fit a temporary cap to stop the gas, and note it in the log with the time and the position.
- Renew the cock at the first opportunity at a shutdown, and check its seating and the pipe connection while it is off.
- Never run with the cock open — it is how water and debris are blown from the cylinder on a first start after shutdown.
Surveyor follow-up: indicator cock capped for six months with the exhaust path proved — is the cap a fix or a deferment?
Full theory: Marine Fuel Testing, ISO 8217 & Combustion Analysis -
14 Main engine lub oil pump low pressure alarm.? What will your action?
Answer
A low lub oil pressure alarm is a stop-or-prepare-to-stop alarm: you do not investigate it with the engine still running.
- On the alarm, check the actual pressure on the gauge and the alarm is not the gauge — the alarm may be a switch failure.
- Check the standby pump is available and started if required, and check the suction strainer and the oil level in the sump and the gravity tank.
- If the pressure does not recover, reduce the load and prepare to stop, because a low-pressure trip on a low lube oil circuit will shut the engine down anyway.
- Do not run on a trip that can go at any moment — the safe action is to slow the engine and shut down to find the cause.
Surveyor follow-up: alarm with a healthy gauge and the standby pump running — is the fault the switch or the lubrication?
Full theory: Two-Stroke Structure — Frame, Tie Rods, Liner, Piston & Crosshead -
15 Main engine safety
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16 With reference to Main Engine Turbo charger (a) What are the indication of water leakage in turbo charger casing. (8) (b) Precaution to be taken during water washing at sea
Answer
Water in the gas space is found at the drain and in the exhaust, and it must not be run with — patch it or stop.
- Indications are water at the turbocharger drain, increased exhaust temperature, and water carried in the exhaust gas.
- A leaking cooler or casing shows as a rising condensate or water level in the drain, sometimes with white deposits in the exhaust.
- A turbocharger should not normally be operated with water leaking into the gas space; bypass the sea cooling if the maker advises it.
- If it must keep running, stop the engine, remove the turbine rotor if needed, and patch the leak temporarily pending a permanent repair or replacement.
Surveyor follow-up: water at the turbo drain with a patched casing at sea — run, throttle back, or stop and strip the rotor?
Full theory: Marine Turbochargers: Aerodynamics, Bearings, Washing & Surge Mitigation -
17 what is automatically controlled in an ME engine
Answer
The main engine automates protection, not judgement: safety cutouts, the fuel control and the governor act without the officer.
- Safety cutouts act automatically — low starting air, low control air, low lube oil and the critical temperature and pressure trips.
- The governor controls the fuel setting to hold the commanded speed, and the fuel control follows the bridge telegraph or the autopilot.
- A crash stop, a slow turn and an emergency stop are executed by the control logic, with the stop valve and the starting air arranged.
- What it never automates is the judgement: monitoring, mode selection, alarm verification and deciding to stop the engine.
Surveyor follow-up: automatic slowdown followed by a trip on a healthy engine — which system acted, and who verifies the alarm?
Full theory: Two-Stroke Main Engine Standby & Start Preparation: Preheating, Turning Gear, Blow-Through & Bridge Control Changeover -
18 what type of pump in ME engine supplies the hydraulic pressure? and how is the pressure varied?
Also asked: “• what type of pump in ME engine supplies the hydraulic pressure? and how is the pressure varied?”
Answer
A gear pump supplies the hydraulic control oil — from the lubrication system or a separate pump on the governor drive — and a relief valve sets the pressure.
- The hydraulic power piston moves the fuel rack, so the governor can apply more power without losing sensitivity.
- Oil is taken from the engine lubrication system, or from a separate gear pump driven off the governor.
- Pressure is set by the relief valve, and a failing relief or a pressure drop is a failed-safe event — the engine must stop.
- The governor itself has two systems: the mechanical ball head sensing speed, and the hydraulic piston valve acting on the fuel setting.
Surveyor follow-up: rack will not move with the governor proved healthy — is it the pressure, the oil or the linkage?
Full theory: Governing and Speed Control — Droop, Load Sharing and the Overspeed Trip -
19 which Main Engine and Aux. Engine
Answer
The main engine is the low-speed two-stroke driving the propeller; the auxiliary engines are the high-speed diesels driving generators.
- The main engine is a large low-speed two-stroke, coupled directly through the shafting to the propeller, and is the ship’s single source of propulsion.
- The auxiliary engines are high-speed four-stroke units coupled to generators, and they provide all the electrical power on board.
- That is why a blackout stops the generators but not necessarily the steering if the steering gear has an independent power source.
- And it is why the two are not interchangeable: they differ in speed, in firing cycle, in fuel system and in how they are controlled.
Surveyor follow-up: main engine out and the ship steering — which arrangement keeps her steerage, and on what power?
Full theory: Diesel Engine Types — 2-Stroke Crosshead vs 4-Stroke Trunk
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.