Author: Daniel G. Teleoaca – Marine Chief Engineer

Imagine a giant, powerful engine churning beneath the waves, propelling a massive ship. While all seems smooth from the outside, within the engine lurks a hidden enemy: torsional vibration.

What are the torsional vibrations and who cause them on a marine engine?

The culprit behind torsional vibrations in a marine engine is the uneven nature of the combustion process within the cylinders.This twisting motion in the crankshaft, caused by uneven firing pulses from the pistons, can wreak havoc on the entire drivetrain if left unchecked. Here’s a breakdown of how it happens:

The Culprit: Uneven Power Delivery

1. • Combustion Pulses: Inside each cylinder, the fuel-air mixture ignites, creating a rapid pressure increase that pushes the piston downwards. This creates a powerful force, but it’s not perfectly smooth.
   • Power Fluctuations: The combustion process isn’t instantaneous, and the force on the piston isn’t constant throughout its travel. The pressure and force peak near the beginning of the power stroke and then taper off as the piston moves down.
   • Varying Torque: This variation in force translates to a fluctuating torque delivered by each connecting rod to the crankshaft. As each cylinder fires in sequence, these torque fluctuations create a pulsating effect on the crankshaft.

The Chain Reaction: Twisting the Crankshaft

• • Twisting Forces: The pulsating torque from the connecting rods tries to twist the crankshaft back and forth with each firing cycle. Imagine someone rapidly twisting a rope back and forth – that’s the essence of torsional vibration.
  • Transfer Through Drivetrain: This twisting motion doesn’t stay isolated in the crankshaft. It travels through the entire drivetrain, including gears, couplings, and shafts, potentially stressing and fatiguing these components.

While combustion is the primary cause, other factors can influence torsional vibrations:

• Engine Design: The number of cylinders, firing order, and crankshaft design all play a role in the frequency and intensity of these vibrations.
• Propeller Load: The resistance offered by the propeller to the engine’s rotation can also affect the vibration patterns.

By understanding these causes, engineers can design engines and utilise torsional vibration dampers to minimise the impact of these twisting forces and ensure a smooth, reliable operation for the entire marine propulsion system.

What is the vibration damper and its purpose?

As the engine runs, pistons fire in sequence, creating a pulsating torque on the crankshaft. This torque tries to twist the crankshaft back and forth, a motion that travels through the drivetrain. Left unchecked, these vibrations can cause excessive stress and fatigue, leading to premature wear, cracks, and even catastrophic failures. The torsional damper steps in to break this cycle.

There are typically three main types of torsional vibration dampers used in marine engines:

• Fluid Viscous Damper: This is the most common type, utilising viscous fluid to absorb vibrations. In a viscous damper, a housing filled with a thick silicone fluid surrounds an inertia ring connected to the crankshaft. During vibration, the relative movement between the crankshaft and ring shears the fluid, generating friction and heat. This dissipates the vibration energy, reducing its impact on the drivetrain.

• Elastomeric Damper: This type relies on the elastic properties of rubber to dampen vibrations. Elastomeric dampers use a rubber element sandwiched between the crankshaft and the outer ring. As the engine vibrates, the rubber acts like a spring, absorbing the twisting motion by deforming slightly. The rubber’s stiffness and design are tuned to target specific vibration frequencies, further minimizing their impact.

• Steel Spring Damper (Geislinger Damper): The torsional vibration steel spring damper, also known as a Geislinger damper (after a prominent manufacturer), offers a distinct operating mode compared to fluid viscous and elastomeric dampers.

The Geislinger damper is a specific type of torsional vibration damper designed to tackle these twisting forces in crankshafts. Here’s the gist of its operation:

• Spring Steel: It uses specially designed leaf springs made from high-grade steel.
• Dual Chamber Design: It has an inner and outer chamber filled with engine oil.
• Vibration Absorption: When the engine vibrates, the outer part twists relative to the inner one, bending the leaf springs.
• Hydraulic Damping: This flexing motion forces engine oil between the chambers. Engine oil’s resistance to flow (hydraulic damping) absorbs the vibration energy.
• Tuned System: The spring stiffness and chamber design are carefully tailored to target and reduce critical resonance frequencies, effectively dampening harmful vibrations.

While these are the most widely used types, research is ongoing, and there might be less common options or variations on these designs existing for specific applications.

Torsional vibration dampers maintenance

Maintenance for a marine engine’s torsional vibration damper typically involves two main approaches: inspection and replacement.

Inspection:

• Visual Checks: During routine maintenance, the damper housing is usually inspected for any cracks, dents, or signs of excessive wear.
• Temperature Monitoring: Some damper types, especially fluid viscous dampers, may involve monitoring their operating temperature. A significant rise in temperature compared to baseline readings might indicate internal issues with the damping material.
• Manufacturer Recommendations: Specific inspection procedures and intervals will depend on the engine manufacturer’s recommendations. They often outline what to look for and how often to perform inspections.

Replacement:

• Service Life: Torsional vibration dampers are designed to last for a certain period, typically measured in operating hours. Marine engine manufacturers specify the recommended replacement interval based on engine design and typical usage patterns.
• Condition-Based Replacement: While following the recommended replacement schedule is important, some signs might necessitate earlier replacement. These include excessive vibration, unusual noises from the damper, or signs of internal leakage (for fluid viscous dampers).

Important points to remember:

• Replacing a torsional vibration damper is usually a job for qualified marine mechanics as it might involve special tools and procedures.
• Neglecting a failing damper can lead to serious consequences, including crankshaft damage, bearing failure, and other expensive repairs.
• Always refer to your specific engine’s manual for detailed information on inspection procedures, replacement intervals, and any special instructions for your damper type.

Torsional vibration damper troubleshooting

Initial Observations:

• Symptoms: Start by noting the symptoms that led you to suspect a damper issue. Does the engine vibrate excessively? Are there unusual noises coming from the damper area?
• Visual Inspection: Perform a thorough visual inspection of the damper itself. Look for any cracks, dents, or signs of wear on the housing. For fluid viscous dampers, check for leaks or discoloration around the seal.

Further Diagnosis:

• Temperature Checks: If possible, check the damper’s operating temperature (refer to manufacturer’s recommendations). A significant rise compared to baseline readings might indicate internal issues with the damping material.
• Listening for Sounds: With the engine idling, carefully listen for any unusual noises coming from the damper area. A grinding noise could indicate internal wear, while a knocking sound might suggest problems with the inertia ring.

Advanced Troubleshooting (if applicable):

• Vibration Analysis (if available): Some modern marine engines might have vibration monitoring systems. If available, consult a qualified engineer to analyse any recorded vibration data. This data can offer insights into the specific frequencies of the torsional vibrations and their severity.

Important Considerations:

• Safety First: Always ensure the engine is off and cool before performing any close inspections.
• Professional Help: For complex issues or any uncertainty, don’t hesitate to seek help from a qualified marine engineer. They can diagnose the problem more accurately and recommend the appropriate course of action.
• Replacement vs. Repair: In most cases, a faulty torsional vibration damper is not repairable and needs to be replaced with a new unit.

By following these steps and considering the additional points, you can gain valuable insights into the potential issues with your marine engine’s torsional vibration damper. Remember, early detection and addressing damper problems can prevent more serious engine damage down the line.

In conclusion a well-functioning torsional vibration damper is vital for the smooth operation, reliability, and longevity of a marine engine. By understanding its role and keeping an eye on your engine’s health, you can ensure a smooth journey for both your ship and its crew.

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Video Source and Credit:

• Simcenter Testing – YouTube
• Geislinger gmBh – YouTube
• Roberto Fuentes – YouTube