Class 2 (2nd Engineer) MEKM 📅 Mar 2023

Exam Question

You have been appointed as Second engineer to a new vessel that experiences severe aft end vibrations. The problem is sought to emanate from the propeller.

Describe the cause of vibration and suggest possible remedies including the selection a new propeller with a different number of bladed. (16)

Reference Answer

Causes of Propeller Vibration
Vibrations are typically caused by an imbalance in the propeller or a phenomenon known as resonance .
Propeller Damage : A damaged or bent propeller blade can create an imbalance. This imbalance causes the propeller to rotate unevenly, generating a force that is transmitted through the propeller shaft to the vessel's hull, causing vibrations.
Resonance : This occurs when the frequency of the forces generated by the propeller's rotation matches the natural frequency of vibration of the ship's hull structure. The primary source of these forces is the propeller blade-frequency , which is the number of blades multiplied by the propeller's revolutions per minute (RPM).

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