Knowledge category
Marine Machinery
Troubleshooting guides for pumps, boilers, purifiers, compressors and auxiliary systems.
What Marine Machinery Covers
The systems and workflows this category answers questions about. Every published answer is listed below.
Main Engine
Fuel injection, cooling, lubrication, exhaust, turbocharger and starting systems.
Auxiliary Engines
Generator engines, load sharing, governors, alarms and routine maintenance.
Pumps
Centrifugal, gear, screw, bilge, ballast, fire and transfer pump troubleshooting.
Boilers & Steam
Burners, water level, feed systems, soot blowing, salinity and steam traps.
Purifiers & Fuel Treatment
Separators, sludge discharge, gravity discs, heaters and fuel quality.
Compressors & Air Systems
Starting air, control air, leaks, intercoolers, drains and safety valves.
Refrigeration & HVAC
Provision plant, AC compressors, expansion valves, gas charging and faults.
Fresh Water Generator
Vacuum loss, scaling, ejectors, salinity, distillate output and cleaning.
Sewage Treatment Plant
Biological treatment, dosing, blowers, discharge limits and common failures.
Oily Water Separator
15 ppm alarms, coalescers, bilge handling, records and MARPOL compliance.
Steering Gear
Hydraulics, pumps, solenoids, alarms, emergency steering and tests.
Electrical Machinery
Motors, alternators, insulation, starters, breakers and earth faults.
Automation & Alarms
Sensors, control loops, shutdowns, PLC signals and alarm investigation.
Troubleshooting Checklists
Step-by-step fault finding for engineers during watch and maintenance.
Current Answers
Why is my marine fuel pump showing low pressure?
A structured checklist for low fuel-pump pressure — suction restrictions, air ingress, relief valves, worn elements and viscosity — before you touch the set point.
Why is my fuel or oil purifier not separating properly?
The usual causes of poor purifier separation — feed rate, temperature, gravity disc and water seal, sludge and bowl condition — and how to work through them one at a time.
Why won't my marine air compressor build pressure?
A compressor that runs but won't fill the receiver usually has leaking valves. Next check the unloader, drains, leaks, cooling, intake filter and piston rings.
What causes a fluctuating water level in a marine boiler?
A swinging boiler water level usually means foaming, priming or shrink and swell, or a false reading from the feed control or gauge glass. Prove it first.
Why is my main engine jacket cooling water temperature high?
Working through high jacket-water temperature — flow, the cooler, the sea and central-cooling side, thermostats, air locks and load.
What causes a scavenge fire in a two-stroke marine engine?
A scavenge fire is the ignition of accumulated oil and carbon in the scavenge spaces of a two-stroke engine — here is why it happens and how to respond.
What causes a crankcase explosion in a marine engine?
Crankcase explosions are caused by oil mist igniting after a hotspot overheats the lubricating oil — understanding the mechanism is key to preventing them.
Why won't the main engine start on air?
A main engine that turns on air but will not fire, or will not turn at all, points to a short list of common causes across the starting-air, fuel and control systems.
Why is the exhaust temperature high on one main engine unit?
A high exhaust temperature on a single cylinder points to that unit's combustion, injection or exhaust valve — a deviation from the others is the key diagnostic clue.
What causes a marine engine turbocharger to surge?
Turbocharger surging is a violent, audible instability of the airflow through the compressor — it signals a mismatch between the turbocharger and the engine's demand.
Why is the main engine lubricating oil pressure low?
Low lubricating oil pressure is a serious alarm that threatens the bearings — the cause is usually in the pump, the filters, the oil itself, or a leak.
How do you recover from a blackout (total loss of electrical power)?
A blackout is the total loss of electrical power on a ship — recovery depends on the emergency generator, restarting the main plant and restoring services in the right order.
Why won't two generators share load equally when running in parallel?
Unequal kW sharing points to the governors and fuel side; unequal current or kVAr points to the AVRs and excitation. Find which one before adjusting anything.
Why does the oily water separator 15 ppm bilge alarm keep activating?
The 15 ppm alarm on the oily water separator stops overboard discharge when the oil content is too high — the causes lie in the separator, the monitor or the feed.
Why does the auxiliary boiler flame keep failing or the burner keep tripping?
Repeated flame failure trips mean the scanner keeps losing the flame, usually because of poor fuel or atomisation, weak ignition, wrong air or a dirty scanner.
How does a marine diesel engine work?
A marine diesel engine converts the chemical energy of fuel into rotary motion through compression ignition — here is the working principle and the two-stroke and four-stroke cycles.
What is the difference between a two-stroke and a four-stroke marine engine?
Two-stroke and four-stroke marine engines differ in how many strokes complete a cycle, their speed and size, and the roles they play aboard ship.
How does a marine boiler work?
A marine boiler generates steam by transferring heat to water — this covers the working principle and the difference between oil-fired and exhaust-gas boilers.
How does a marine centrifugal oil purifier work?
A marine purifier spins fuel or lube oil in a fast bowl so water and solids are flung out by centrifugal force. How the bowl works and what controls separation.
How does a marine engine turbocharger work?
A turbocharger uses exhaust gas to spin a turbine that drives a compressor, pushing extra air into the cylinders so the engine can burn more fuel.
How does a marine fresh water generator (evaporator) work?
A fresh water generator makes drinking and technical water from seawater by boiling it under vacuum using waste heat from the engine, then condensing the vapour.
How does a marine air compressor work and why is it needed?
A marine air compressor squeezes air in stages to high pressure and stores it in receivers, chiefly to provide the starting air that turns large diesel engines over.
What is cylinder lubrication in a two-stroke marine engine?
Cylinder lubrication is the separate oil supply fed onto the liner of large two-stroke engines to lubricate, neutralise fuel acids and keep the surfaces clean.
What is the emergency procedure if the steering gear fails?
Steering gear failure is a serious emergency handled by switching to the standby power unit or emergency steering and warning other ships, backed by SOLAS redundancy.
How does a ship's refrigeration plant work?
A marine refrigeration plant uses the vapour-compression cycle to move heat out of provision rooms or cargo spaces, keeping food and cargo cold at sea.
What is the difference between a purifier and a clarifier?
A purifier removes water and solids from oil and has a water outlet. A clarifier removes only solids, has no water outlet and suits oil with very little water.
How does a ship's steering gear work?
The steering gear is the powered hydraulic machinery that turns the rudder in response to helm orders from the bridge, using rams or rotary vanes driven by pumps.
How does a marine incinerator work and what can it burn?
A marine incinerator burns the ship's waste oils, sludge and solid garbage in a combustion chamber, subject to MARPOL rules on what may be incinerated and where.
How does a ship's sewage treatment plant work?
A marine sewage treatment plant breaks down the ship's sewage — usually biologically — and disinfects it so that the treated effluent meets MARPOL Annex IV discharge standards.
What is a central cooling system on a ship and why is it used?
A central cooling system uses seawater to cool a closed freshwater circuit, which in turn cools the machinery — reducing seawater corrosion and fouling in the equipment.
What is jacket cooling water in a marine engine?
Jacket cooling water is the treated fresh water circulated through the passages, or jackets, around an engine's cylinders to carry away combustion heat and keep it at its correct working temperature.
How does a marine centrifugal pump work?
A centrifugal pump moves liquid by spinning it with an impeller, which throws the liquid outward and converts its speed into pressure — the most common type of pump aboard ship.
Why does a marine centrifugal pump lose suction or stop pumping?
A centrifugal pump loses suction when air breaks its prime or the suction is starved: leaking joints, choked strainers, low levels or cavitation.
What is cavitation in pumps and propellers?
Cavitation is the forming and collapse of vapour bubbles where liquid pressure drops too low. It pits impellers and propellers and causes noise and vibration.
How does a marine heat exchanger work?
A heat exchanger moves heat from a hot fluid to a cooler one through a metal wall without mixing them. Shell-and-tube and plate types and how fouling shows up.
What is a governor on a marine engine and what does it do?
A governor automatically controls an engine's speed by adjusting the fuel supply to match the load, keeping the engine at the required revolutions or a generator at constant frequency.
What is a thrust bearing or thrust block and what does it do?
A thrust bearing, or thrust block, takes the push of the propeller along the shaft and passes it into the hull, so the propeller's thrust moves the ship.
What is the difference between a controllable-pitch and a fixed-pitch propeller?
A fixed-pitch propeller has blades set at one angle. A controllable-pitch propeller turns its blades to vary thrust and go astern without reversing the shaft.
What is scavenging in a two-stroke marine engine?
Scavenging is the process of pushing the burnt exhaust gases out of a two-stroke engine cylinder and replacing them with fresh air, ready for the next combustion cycle.
What is a bearing and what types are used in marine engines?
A bearing supports and locates a rotating shaft while allowing it to turn with little friction — marine engines rely on plain white-metal bearings lubricated by an oil film.
What is the stern tube and stern tube seal on a ship?
The stern tube carries the propeller shaft out through the hull and holds its bearings. Seals at each end keep seawater out and the lubricant in.
What is an indicator diagram and what does it tell the engineer?
An indicator diagram plots the pressure inside an engine cylinder against volume or crank angle, letting the engineer assess the power, condition and faults of each cylinder.
What is a shaft generator and why is it used?
A shaft generator is an alternator driven by the main engine or propeller shaft that supplies the ship's electrical load at sea, so auxiliary engines can stop.
How does a ship's fuel oil system store, treat and deliver fuel to the engine?
The fuel oil system takes bunkers from the storage tanks, settles and purifies them, heats heavy fuel to the right viscosity, and delivers clean fuel under pressure to the engine.
What is a reduction gearbox on a ship and why is it used?
A reduction gearbox lowers the high rotational speed of a medium- or high-speed engine to the slower speed that turns an efficient propeller, and can combine several engines onto one shaft.
Why is boiler water treated on a ship and how?
Boiler water is chemically treated and tested to prevent scale, corrosion and carryover, which would damage the boiler, reduce its efficiency and threaten safety.
