Vibrations in diesel machinery and shafting are caused by oscillatory or intermittent forces within the engine and transmission system. They may be longitudinal, axial, transverse, or torsional in nature. The main causes are:

1. Constantly changing firing pressures in the cylinders.
2. Unbalanced forces, couples, and moments generated by reciprocating and rotating masses.
3. Gas forces, including pulsation of exhaust gases.
4. Guide force moments acting on crosshead guides.
5. Axial forces due to in-plane bending of crank webs.
6. Variations in torque and propeller thrust, leading to torsional vibrations in the shaft line.
7. Severe vibrations when machinery or the propeller resonates with the natural frequency of the ship’s hull/structure.
8. External factors such as damaged or unbalanced propeller, worn bearings (intermediate shaft bearings, stern tube bushes), and structural weaknesses in the hull transmitting vibration to shafting.
9. Cyclic forces from the ship’s motion through water.

• Carry out regular maintenance and overhauls to ensure good combustion and minimize mechanical wear.
• Operate the engine away from critical speeds and barred speed ranges; these ranges must be passed quickly to avoid resonance.
• Maintain proper alignment of shafting and bearings.

1. Compensators/Balancers
   • Counter vibrations due to reciprocating and rotating masses.
   • Rotating at engine speed to cancel 1st order frequency and at twice engine speed for 2nd order frequency.
   • Usually positioned in chain drives.
2. Dampers/Detuners
   • Axial Vibration Dampers fitted at the free end of the crankshaft to reduce axial vibration caused by crank web bending.
   • Torsional Vibration Dampers/Detuners installed at the aft end of the engine or incorporated into the flywheel to reduce torsional vibration from torque fluctuations and propeller thrust.
   • Frequency Control Devices alter the natural frequency of the system.
3. Top Bracing
   • Provides stiffness to reduce guide force moment–induced vibrations.

On Machinery

• High-amplitude vibrations cause severe stress, leading to early fatigue failure of components.
• Micro-level defects can develop into surface or subsurface cracks, propagating to material failure.
• Leads to loosening of bolts, misalignment, excessive wear, and structural damage.
• Reduces efficiency and overall service life of machinery.

On Crew Members

• Causes fatigue, loss of balance, general shakiness, stomach disorders, headaches.
• Prolonged exposure leads to discomfort, reduced work performance, and potential long-term health issues.
• Increased noise levels from vibration may cause hearing damage.