Aux 1 Unit 11 Q7

Type: Highly Flexible Rubber Element Coupling

This type of coupling is a popular choice for main propulsion drives due to its ability to accommodate significant misalignment and dampen vibrations, while still transmitting high torque loads reliably.

Key Components:

1. Hubs:
   • Two metal hubs, one connected to the engine or gearbox shaft and the other to the propeller shaft.
   • Typically made of steel or cast iron for strength and durability.
2. Flexible Element:
   • A series of rubber or elastomeric elements, often arranged in a grid or star pattern, connect the two hubs.
   • These elements are the heart of the coupling, providing the flexibility and misalignment compensation.
   • They are designed to withstand the torsional loads and shear forces transmitted through the shafting system.
3. Bolts or Clamping Mechanism:
   • The hubs are bolted or clamped to the flexible element, creating a secure assembly.

Operation:

1. Torque Transmission: Torque is transmitted from the engine/gearbox shaft to the propeller shaft through the hubs and the flexible element.
2. Misalignment Compensation:

• Angular Misalignment: The flexible elements can bend and twist to accommodate angular misalignment (when the shafts are not parallel).
• Axial Misalignment: They can also compress or extend to compensate for axial misalignment (when the shafts are not in the same plane).
• Parallel Misalignment: The flexible elements can slightly deform to handle parallel misalignment (when the shafts are parallel but offset).

3. Vibration Dampening:

• Shock Absorption: The rubber or elastomeric elements absorb and dampen vibrations and shock loads generated by the engine or propeller, protecting the shafting system and reducing noise and wear.

Advantages for Main Propulsion Drive:

• High Torque Capacity: Can handle the high torque loads associated with main propulsion shafts.
• Misalignment Compensation: Accommodates significant misalignment, crucial in marine environments where the ship’s structure can flex and deform due to loads and sea conditions.
• Vibration Dampening: Reduces vibrations transmitted from the engine to the propeller and vice-versa, improving comfort and reducing wear on components.
• Electrical Insulation: The rubber element provides electrical insulation between the shafts, preventing galvanic corrosion.
• Maintenance-Free: Typically requires no lubrication or regular maintenance.

Disadvantages:

• Limited Torsional Stiffness: Compared to some other coupling types, they might have slightly lower torsional stiffness (resistance to twisting), which can affect the precision of power transmission in some applications.
• Temperature Limitations: The rubber or elastomeric elements have temperature limitations, so they might not be suitable for extremely high-temperature applications.

Example: A common type of highly flexible rubber element coupling used in main propulsion drives is the Geislinger coupling, known for its high torque capacity, excellent misalignment compensation, and vibration dampening capabilities.

In summary, a highly flexible rubber element coupling is a suitable choice for a main propulsion drive due to its ability to handle high torque loads, accommodate significant misalignment, and dampen vibrations, all while being relatively maintenance-free.

Flexible couplings are crucial components in propulsion drives, serving several important purposes that contribute to the system’s efficiency, reliability, and longevity. Here are some key reasons for their use:

1. Accommodate Misalignment:

• Shaft Misalignment: It’s virtually impossible to achieve and maintain perfect alignment between the engine/gearbox shaft and the propeller shaft due to factors like:
  • Manufacturing Tolerances: Slight variations in the dimensions and alignment of components during manufacturing.
  • Installation Errors: Imperfections in the installation process can lead to initial misalignment.
  • Thermal Expansion: Temperature changes during operation cause the shafts and other components to expand and contract, potentially leading to misalignment.
  • Vessel Flexing: The ship’s structure can flex and deform under load and sea conditions, causing further misalignment.
• Prevent Damage & Wear: Flexible couplings can bend, twist, or compress to accommodate these misalignments, preventing excessive stress and wear on the shafts, bearings, and seals. This helps to avoid premature failure and costly repairs.

2. Absorb Vibrations and Shock Loads:

• Engine Vibrations: The engine, especially diesel engines, generates vibrations that can be transmitted through the shafting system.
• Propeller-Induced Vibrations: The propeller also generates vibrations and shock loads, especially in rough seas.
• Dampening Effect: Flexible couplings, particularly those with rubber or elastomeric elements, act as shock absorbers, dampening these vibrations and preventing them from being transmitted to the rest of the system.
• Reduced Noise and Fatigue: This leads to reduced noise and vibration levels on board, improving passenger and crew comfort, and reducing the risk of fatigue-related failures in the shafting and connected equipment.

3. Electrical Insulation:

• Galvanic Corrosion: In marine environments, dissimilar metals in contact with seawater can lead to galvanic corrosion, where one metal corrodes preferentially.   1. Battling the Corrosive Properties of Seawater – Ocean Observatories Initiative oceanobservatories.org
• Isolation: Some flexible couplings, like those with rubber elements, provide electrical insulation between the shafts, preventing the flow of electrical current and mitigating galvanic corrosion.

4. Ease of Installation and Maintenance:

• Simplified Alignment: Flexible couplings allow for some tolerance in alignment during installation, making the process easier and less time-consuming.   1. Align Your Machines Using Coupling Tolerances | Benchmark PDM benchmarkpdm.com
• Easier Maintenance: Some types of flexible couplings, like rubber element couplings, require minimal maintenance and don’t need lubrication, reducing downtime and maintenance costs.

Specific Benefits in Main Propulsion Drives:

• High Torque Transmission: Flexible couplings used in main propulsion drives are designed to handle the high torque loads associated with transmitting power from the engine to the propeller.
• Reliable Operation: They provide a reliable and efficient connection between the shaft sections, even in the presence of misalignment, vibrations, and shock loads.
• Reduced Downtime: Their ability to accommodate misalignment and their low maintenance requirements contribute to reduced downtime and increased operational efficiency.

In conclusion, flexible couplings are essential components in propulsion drives, providing flexibility, vibration dampening, and electrical insulation, all of which contribute to the smooth, efficient, and reliable operation of the system. They play a crucial role in protecting the shafting, bearings, and other components from damage, ensuring the vessel’s propulsion system performs optimally and safely.Sources and related content