Class 2 (2nd Engineer) MEKG 📅 Jun 2024

Exam Question

With reference to shaft alignment:

(a) Explain the meaning of fair curve or rational alignment (8)

(b) Shaft alignment is often verified using hydraulic jacks to obtain a simple graph. Sketch such a graph, indicating the following: (8)

(i) Static load

(ii) Hysteresis

(iii) Influence number

(iv) Explain the limitations of checking shaft alignment solely by hydraulic jacking methods.

Reference Answer

### (a) Fair Curve or Rational Alignment
Rational alignment, also known as fair curve alignment, is a modern engineering approach to shafting installation that deliberately sets the shaft bearings in a predetermined smooth curve (a 'sagged' or 'hogged' profile) in the static, cold condition. This is in contrast to the traditional 'bore' alignment method, which aimed for a perfectly straight line.
**Core Concept:**
The fundamental principle is to create a calculated 'misalignment' in the static state to achieve an optimal, near-straight alignment under dynamic operating conditions at sea. This approach accounts for various forces and deflections that the traditional straight-line method ignores.

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