Marine Engineering Knowledge: Main Propulsion and Auxiliary Machinery
This domain tests whether you understand the machinery that drives the ship and the auxiliaries that keep it alive: configuration, operating limits, and the diagnostics an officer of the watch is expected to apply unsupervised.
Main propulsion
Slow-speed two-stroke crosshead diesels (roughly 70-120 rpm) drive a fixed-pitch propeller directly and burn residual fuel via high-pressure injection. Medium-speed four-stroke engines (400-1000 rpm) usually drive a controllable-pitch propeller through reduction gearing, which allows constant-speed running for shaft generators. Know the sub-systems: starting air at about 30 bar, fuel booster and viscosity control (typically 10-15 cSt at injection), cylinder lubrication, scavenge air and turbocharging, jacket cooling, and the stern tube.
Auxiliaries
Boiler and feed system, fuel and lube oil purifiers, air compressors and air bottles, fresh water generator, steering gear (SOLAS requires two independent power units and a duplicate power supply), bilge and ballast pumps, and the emergency generator.
Worked example
An engine develops 900 kW at service load and the test-bed specific fuel consumption is 185 g/kWh. Daily consumption = 185 x 900 x 24 = 3,996,000 g, about 4.0 t/day. Adding a 0.5 t/day margin for pilot fuel and sludge gives a planned 4.5 t/day. The reasoning: SFOC is grams per kilowatt-hour, so multiply by power first, then by 24 hours.
Traps
Using MCR power instead of actual service load; mixing kg/h with g/kWh; forgetting that SFOC rises at part load; assuming the emergency generator can carry the whole switchboard.