Marine Engineering Knowledge and Machinery Operation
Core concepts
The watchkeeping engineer must be able to explain, not just operate, the machinery plant. Expect questions on the diesel cycle and indicated/brake mean effective pressure, specific fuel consumption, scavenging and turbocharging, cooling water treatment, lubricating oil properties (viscosity grade, TBN, base number depletion), fuel oil characteristics (density, viscosity, sulphur, pour point, cetane), and the sequence of starting, manoeuvring and stopping a main engine. Understand line-shafting arrangements, thrust and stern tube bearings, reduction gearing and clutch types, and the causes of vibration and misalignment.
Traps
- Confusing indicated power (from indicator diagrams) with brake power (shaft). Mechanical efficiency is brake/indicated, always below unity.
- Mixing viscosity classification systems: ISO VG for lubricants, kinematic viscosity in cSt at 40 °C or 50 °C for fuels.
- Forgetting that TBN of cylinder oil must match fuel sulphur; over-basing causes deposits.
- Assuming higher compression ratio always gives better economy; ignition delay and knock limit it.
- Misreading scavenge fire symptoms (high exhaust temperature, smoky turbocharger, surging) as turbocharger failure.
Worked example / rule of thumb
If indicated power is 6 000 kW and brake power 5 400 kW, mechanical efficiency = 5 400/6 000 = 90 %. Rule of thumb: a two-stroke crosshead engine uses cylinder oil at a feed rate set by fuel sulphur, typically 0.8–1.2 g/kWh for high-sulphur fuel; always confirm from the maker's manual rather than memory.