Class 2 (2nd Engineer) MEKG 📅 Jan 2025

Exam Question

(a) Explain why, in spite of accurate alignment under static conditions use of flexible couplings and copious supply of lubricant, main reduction gearing in still subject to pitting, scuffing and other tooth service. (8)

(b) Discuss the significance of viscosity in relation to the function of marine turbine oils as used in main propulsion installations, stating how the viscosity is controlled and what could cause it to change in service. (8)

Reference Answer

### Part (a): Main Reduction Gearing Failures (8 Marks)
Despite meticulous static alignment, the use of flexible couplings, and a constant supply of high-quality lubricant, main reduction gearing remains susceptible to surface failures like pitting and scuffing due to the severe and dynamic operating environment onboard a ship. The primary reasons are the limitations of static setup in a dynamic environment and the inherent physical limits of lubrication and materials.
**1. Dynamic Misalignment and Loading:**
* **Hull Deflection:** The ship's hull is not a rigid structure. It constantly flexes and twists due to wave action (hogging, sagging), loading changes, and thermal effects. This distorts the engine and gearbox foundations, transforming perfect static alignment into dynamic misalignment during operation. This transient misalignment concentrates loads on small areas of the gear teeth, exceeding design contact stresses.

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