Class 2 (2nd Engineer) MEKG 📅 Jun 2023

Exam Question

Misalignment of the main shafting between engine and propeller causes bearing overloads and shaft stress.

(a) State the difficulties associated with checking shaft alignment and the reason why results are unreliable due to external factors (6)

(b) Explain with a simple sketch how a bearing load is assessed (5)

Reference Answer

### (a) Difficulties in Shaft Alignment Checks and Reasons for Unreliability
A comprehensive shaft alignment check is subject to numerous inherent difficulties and external variables that can render the results unreliable or specific only to the condition at the time of measurement.
**(i) Difficulties Associated with Checking Shaft Alignment (Inherent Factors):**
* **Hull Deflection (Afloat vs. Ashore):** A vessel's hull structure behaves differently when berthed in a drydock compared to being afloat. When afloat, hydrostatic pressure and buoyancy forces cause the hull to flex, altering the baseline upon which the engine and shafting are mounted. Alignment performed in drydock must account for this predicted deflection.

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