BD Marine Engineer Class 2 (Second Engineer) key terms

The average pressure that, if applied to the piston throughout its power stroke, would produce the measured shaft output of an engine. It allows engines of different sizes and speeds to be compared for loading.

A pressure-volume or pressure-crank angle plot taken from a cylinder, used to check combustion quality, peak pressure and power balance between units. Deviations reveal injection timing faults, worn rings or overload.

The crank angle at which fuel injection begins relative to top dead centre. Too early raises peak pressure and mechanical stress; too late causes afterburning, high exhaust temperature and smoky operation.

Fresh charge air supplied by the turbocharger to clear burnt gases from the cylinder and provide oxygen for combustion. Insufficient scavenging causes incomplete combustion, high exhaust temperatures and loss of power.

Unstable flow through the compressor in which delivery pressure and flow oscillate violently, producing a characteristic barking noise. Causes include fouled turbine, blocked air cooler or rapid load change.

A heat exchanger that cools compressed scavenge air before it enters the cylinder, increasing its density and therefore the mass of oxygen trapped for combustion. Fouling here raises exhaust temperatures and reduces engine power.

The mass of fuel burned per unit of shaft work produced, usually expressed in grams per kilowatt-hour. It is the standard measure of engine efficiency and is corrected to reference conditions for comparison.

The quantity of heat released when a unit mass of fuel is completely burned. It determines the fuel's energy content and is used with flow measurements to calculate engine efficiency and boiler output.

A measure of a fuel's resistance to flow, which falls as it is heated. Heavy residual fuels must be heated to a specified viscosity at the injector for correct atomisation and complete combustion.

A violent ignition of oil mist that forms when hot spots vaporise lubricating oil in the crankcase. Prevention relies on oil mist detection, prompt slowing of the engine and keeping hot surfaces and relief valves in order.

A device that continuously samples crankcase atmosphere and alarms when the density of suspended oil droplets rises above a safe level, giving early warning of overheating bearings or pistons before an explosion can occur.

A spring-loaded non-return valve fitted to crankcase doors that opens to release pressure from a primary explosion and closes to prevent air entering and supporting a secondary, more destructive explosion.

The bearing supporting the propeller shaft where it passes through the hull, lubricated by oil or seawater. Excessive wear or seal failure causes vibration, oil leakage and possible water ingress into the ship.

A periodic inspection in which the propeller shaft is withdrawn or examined in situ to check bearing wear-down, seal condition and shaft integrity. Results are recorded and compared with previous readings to detect deterioration.

A slip-ring and brush arrangement that electrically bonds the propeller shaft to the hull, preventing stray currents from causing electrochemical corrosion of the shaft and stern tube bearings.

A system that passes a controlled direct current through sea water to anodes to protect immersed steel from corrosion. Output must be monitored and adjusted for coating condition and salinity.

A block of a less noble metal, such as zinc or aluminium alloy, bolted to steel structures so that it corrodes preferentially and protects the steel. Anodes are inspected and renewed as they waste away.

The procedures and treatment systems used to control the transfer of harmful aquatic organisms in ballast water, including exchange, filtration and disinfection, with records kept in a Ballast Water Record Book.

A statutory register in which all oil transfers, discharges, tank cleanings and machinery-space bilge movements are recorded. Entries must be truthful and signed, and are inspected during port State control.

The chapter of the international convention for prevention of pollution from ships that regulates oil discharges, requiring equipment such as oily water separators, 15 ppm alarms and sludge retention facilities.

Equipment that reduces the oil content of machinery space bilge water to not more than 15 parts per million before discharge, normally using gravity separation followed by coalescing or filtration stages.

A designated sea area in which stricter limits apply to the sulphur content of fuel oil or to equivalent exhaust gas cleaning, requiring compliant fuel, changeover records and careful fuel system management.

An exhaust gas after-treatment method that injects a reducing agent such as urea over a catalyst to convert nitrogen oxides into nitrogen and water, helping engines meet Tier III emission limits.

A computerised or paper schedule of routine inspections, servicing and overhauls based on running hours or calendar intervals, providing records that demonstrate machinery has been maintained to class and statutory requirements.

The practice of measuring parameters such as vibration, temperature, oil analysis and performance trends to detect developing faults, allowing maintenance to be planned before failure rather than at fixed intervals.

Interpretation of measured vibration amplitude and frequency spectra to identify faults such as unbalance, misalignment, bearing damage or loose components in rotating machinery before they cause breakdown.

Formation and collapse of vapour bubbles in a liquid where local pressure falls below vapour pressure, causing noise, erosion and loss of performance in pumps and propellers.

The margin by which the absolute pressure at a pump suction exceeds the liquid's vapour pressure. Insufficient margin leads to cavitation, reduced delivery and damage to impeller and casing.

A rotodynamic machine that throws liquid outward by a rotating impeller to create flow and head. It is normally started with the discharge valve closed or throttled and must not run dry.

The arrangements, drills and procedures that allow the rudder to be controlled after failure of the main steering power, using an alternative power source or manual means within a specified time.

An independently driven generator, with its own fuel supply and starting means, that automatically supplies essential services such as steering gear, emergency lighting and radio equipment when the main supply fails.

The sequence by which propulsion and electrical power are restored after a total loss of supply, including automatic starting of the emergency generator and controlled restarting of essential auxiliaries.

A condition in which the main propulsion plant, boilers and auxiliaries are out of action because of loss of main power, from which the ship must be able to recover without external assistance.

A periodically unattended engine room approved by the administration, requiring alarms, safety devices, fire detection and automatic control to be tested and proved operational before the ship sails.

A timer-based alarm in the engine room that requires the duty engineer to reset it at set intervals, alerting others if the engineer becomes incapacitated while the space is unattended.

The networked sensors, displays and audible alarms that inform the watchkeeper of abnormal temperatures, pressures and levels, with safety interlocks that may slow down or stop machinery automatically.

The apparent rise in a ship's centre of gravity caused by liquid moving freely in a partly filled tank, reducing transverse stability. Pressing up or emptying tanks limits the loss of metacentric height.

The vertical distance between the centre of gravity and the transverse metacentre. A small positive value gives a stiff or tender ship, while a negative value indicates an unstable condition.

The angle to which a ship with negative initial stability heels and settles, where the centre of buoyancy shifts enough to restore equilibrium. It is corrected by lowering the centre of gravity, not by adding ballast high up.