Class 2 (2nd Engineer) MEKG 📅 Jan 2024

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 damage. (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 Damage
Despite meticulous static alignment, the use of flexible couplings, and an abundant supply of high-quality lubricant, main reduction gearing remains susceptible to surface damage like pitting and scuffing due to the severe dynamic conditions experienced in a marine environment. The static, cold state does not represent the reality of a vessel underway.
**1. Dynamic Misalignment and Load Fluctuation:**
* **Hull Deflection:** A ship's hull is a flexible structure that constantly bends and twists in a seaway (hogging, sagging, and torsional flexing). This structural deformation is transmitted through the engine and gearbox foundations, causing significant dynamic misalignment between the pinions and wheels. Flexible couplings can only accommodate a fraction of this large-scale, low-frequency movement.

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