With reference to comparing modern water lubricated stern tube bearings with those that are oil lubricated:
(a) state THREE advantages; (3)
(b) state THREE disadvantages, explaining how EACH may be overcome.(7)
Modern water lubricated stern tube bearings?
Modern water-lubricated stern tube bearings represent a significant advancement in marine propulsion technology, offering a more environmentally friendly and efficient alternative to traditional oil-lubricated bearings.
1. Water or oil? Choosing the best option to lubricate your bearings – Riviera Maritime Media
Key Features:
- Lubricant: Instead of oil or grease, they use seawater as the lubricant, eliminating the risk of oil pollution and reducing environmental impact. 1. COMPAC Open Seawater Lubricated Propeller Shaft System – Thordon Bearings thordonbearings.com
- Bearing Material: Typically made from advanced polymer materials or specially formulated rubber compounds that exhibit excellent wear resistance and low friction properties even when lubricated with water.
- Open or Closed Loop System:
- Open Loop: Seawater is drawn directly from the surrounding environment, passes through the bearing, and is discharged back into the sea.
- Closed Loop: A dedicated seawater circulation system with filters and coolers is used to provide clean and controlled lubrication.
Advantages of Modern Water-Lubricated Stern Tube Bearings:
- Environmental Friendliness:
- Eliminates the risk of oil pollution from leaks or spills, complying with stringent environmental regulations and reducing potential fines. 1. COMPAC Open Seawater Lubricated Propeller Shaft System – Thordon Bearings thordonbearings.com
- Reduced Maintenance:
- No need for regular oil changes, oil filter replacements, or complex oil monitoring systems, resulting in lower maintenance costs and less downtime.
- Lower Operating Costs:
- Eliminates the need to purchase and manage lubricating oil, further reducing operating expenses.
- Improved Efficiency:
- Advanced bearing materials and designs can offer comparable or even superior performance to oil-lubricated bearings in terms of friction and wear, leading to improved propulsion efficiency.
Challenges and Solutions:
- Load Capacity: Traditionally, water-lubricated bearings had a lower load capacity compared to oil-lubricated ones. However, modern materials and designs are closing this gap. Careful propeller design and selection are important to ensure sufficient load handling for modern vessels.
- Wear Rate: Water can be more abrasive than oil, potentially leading to higher wear rates. This is mitigated by using advanced bearing materials specifically designed for water lubrication. Regular monitoring and maintenance are crucial.
- System Complexity: Some water-lubricated systems, particularly those with closed-loop circulation, can be more complex than simpler oil-lubricated systems. However, the reduced maintenance and environmental benefits often outweigh this complexity.
Applications:
- Wide range of vessels: Modern water-lubricated stern tube bearings are becoming increasingly popular for various types of ships, including tankers, bulk carriers, container ships, ferries, and even some superyachts.
- Environmentally Sensitive Areas: They are particularly beneficial for vessels operating in environmentally sensitive areas where the risk of oil pollution is a major concern.
In summary: Modern water-lubricated stern tube bearings offer a sustainable and increasingly viable alternative to traditional oil-lubricated bearings. They eliminate the risk of oil pollution, reduce maintenance requirements, and offer potential efficiency gains, making them an attractive choice for many ship owners and operators who prioritize environmental responsibility and cost-effectiveness.Sources and related content
Oil lubricated stern tube bearings
Oil-lubricated stern tube bearings are essential components of a ship’s propulsion system. They support the propeller shaft where it passes through the stern tube, enabling smooth rotation and transmitting power from the engine to the propeller. These bearings use lubricating oil to minimize friction and wear between the rotating shaft and the stationary bearing surface.
1. Stern Tube Explained | Location, Parts and Purpose – Nautilus Shipping
Key Features:
- Lubrication: Utilize lubricating oil to create a hydrodynamic film between the shaft and bearing, reducing friction and wear. 1. Differences Between Oil-Lubricated and Water-Lubricated Stern Tube Bearings wildonengineering.com.au
- Bearing Material: Typically lined with white metal (babbitt), a soft alloy with good embedability and conformability to the shaft. 1. Stern Tube Bearing – Lagersmit www.lagersmit.com
- Oil Circulation System: A dedicated system circulates and cools the oil, ensuring adequate lubrication and preventing overheating.
Components:
- Stern Tube: A cylindrical housing attached to the hull, through which the propeller shaft passes. 1. WHAT IS A STERN TUBE? – Lagersmit www.lagersmit.com
- Bearing Bushings: One or more bearing bushings, lined with white metal, are fitted within the stern tube, providing the bearing surface for the shaft. 1. Sterntube bearings – Wärtsilä www.wartsila.com
- Shaft Seals: Seals at both ends of the stern tube prevent oil leakage and water ingress. 1. Oil-lubricated sterntube seals – SKF www.skf.com
- Oil Circulation System: Includes an oil pump, cooler, filters, and piping to circulate and maintain the oil within the bearing.
Working Principle:
- Hydrodynamic Lubrication: As the shaft rotates, it drags oil into the bearing clearance, creating a pressurized oil film that separates the shaft from the bearing surface. This film supports the shaft’s weight and reduces friction. 1. Stern Tube Bearing – Lagersmit www.lagersmit.com
- Oil Circulation: The oil circulation system continuously pumps oil into the bearing, ensuring adequate lubrication and removing heat generated by friction.
- Oil Cooling: The oil cooler helps maintain the oil’s temperature within safe limits, preventing overheating and degradation.
Advantages:
- High Load Capacity: Oil-lubricated bearings can handle high radial loads from the propeller shaft and thrust loads from the propeller.
- Good Damping: The oil film provides good damping, reducing vibrations and noise. 1. Differences Between Oil-Lubricated and Water-Lubricated Stern Tube Bearings wildonengineering.com.au
- Long Service Life: With proper maintenance, they can have a long service life. 1. Stern Tube Explained | Location, Parts and Purpose – Nautilus Shipping www.nautilusshipping.com
Disadvantages:
- Environmental Risk: Potential for oil leakage into the marine environment, posing a pollution risk. 1. Water-lubricated bearings prevent oil leaks from shaftlines – Riviera Maritime Media www.rivieramm.com
- Maintenance Requirements: Requires regular oil changes, filter replacements, and monitoring of oil condition. 1. Sterntube Bearings – AtZ Marine Technologies atzmartec.com
- Complexity: The oil circulation system adds complexity to the stern tube arrangement.
Applications:
- Widely used in various types of ships, particularly larger vessels and those operating in harsh conditions where high loads and reliable performance are critical.
In Summary:
Oil-lubricated stern tube bearings are essential components of marine propulsion systems, providing reliable support and lubrication for the propeller shaft. While they require regular maintenance and pose a potential environmental risk due to oil leakage, their high load capacity, good damping, and long service life make them a preferred choice for many marine applications.