With reference to the crankshaft deflection of main engine crank shaft,
(a) State the ideal condition required before taking deflections.
(6)
(b) How is the accuracy of the reading taken are ensured?
(6)
(c) What is the purpose of taking deflection and how is the readings taken interpreted?
(4)
Reference Answer
### (a) Ideal Conditions Required Before Taking Deflections (6 Marks) To obtain accurate and repeatable crankshaft deflection readings, a set of stringent conditions must be met. These conditions ensure that external influences are minimized and the readings reflect the true alignment of the crankshaft bearings. 1. **Vessel Condition**: The vessel must be afloat in calm sea conditions with minimal swell. The hull should be on an even keel, and drafts should be stable and recorded. Taking readings during cargo operations, ballasting, or in heavy seas is prohibited as the resulting hull stresses (hogging/sagging) will be transmitted to the engine bedplate, causing erroneous readings. 2. **Engine Temperature**: The engine must be in a 'cold' state. This means the engine has been shut down for a sufficient period (typically 12-24 hours) to allow the crankshaft, bedplate, and crankcase to reach a uniform, stable ambient temperature. This eliminates errors caused by thermal expansion of the components.
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