Maintenance, Repair and Machinery Condition Monitoring
Core concepts
This domain tests planned maintenance systems, condition monitoring and defect analysis. Know the machinery planned maintenance scheme required by the ISM Code and class societies, and the difference between planned, preventive, predictive and corrective maintenance. Condition monitoring covers vibration analysis (unbalance, misalignment, bearing defect frequencies), thermography, oil analysis (spectrographic wear metals, viscosity, water content, total base number), and performance trending such as exhaust temperature and fuel index deviation. Understand wear limits, ovality and taper measurement of cylinder liners, crankshaft deflection and its meaning for bedplate alignment, and the use of ultrasonic thickness measurement for structures and piping. Dry docking and survey preparation, spare gear management and critical spares are also fair game.
Traps
A frequent trap is treating crankshaft deflection readings taken in warm conditions as directly comparable to cold readings. Another is assuming increased vibration always means bearing failure; looseness, cavitation and resonance are alternatives. Questions on oil analysis may test the difference between wear-metal concentration trends and a single high reading; trend matters more than absolute value. Distinguish total base number (reserve alkalinity) from total acid number.
Worked rule of thumb
For trend-based decisions, use three consecutive samples or readings to confirm a direction. If a liner wear rate exceeds roughly 0.1 mm per 1000 hours, investigate fuel sulphur, cylinder oil feed rate and scavenge conditions before scheduling renewal.