The definition of stern tube: a pipe section fixed at the stern of the ship, which allows the shaft to pass through and is equipped with sealing and supporting devices.

The composition of the stern tube: front bearing seat+connecting tube (seamless tube)+rear bearing seat

Front and rear bearing seats (water lubricated): including polymer/rubber bearings;

Front and rear bearing seats (oil lubricated): including white alloy bearings

Production cycle: 30 days

Warranty period: 1 year

Certificates available: CCS type approval certificate, CCS product certificate, Korean KR, German GL, French BV and other certificates.

Definition and Function

The stern tube is an important component in the ship's shaft system. It is a tubular structure that surrounds the stern shaft (propeller shaft) and is installed at the stern of the ship. Its main function is to support and protect the stern shaft, provide precise installation position for the stern shaft, ensure stable rotation of the stern shaft, and also play a sealing role to prevent seawater from entering the ship's body.

Structural composition

Shell part:

The outer shell of the stern tube is usually made of metal materials such as cast iron or steel. It has sufficient strength and stiffness to withstand various forces such as the weight of the stern shaft, the thrust of the propeller, and the pressure of seawater. The shape of the outer shell is generally cylindrical, and the dimensions of its inner and outer diameters are determined based on factors such as the size of the vessel and the specifications of the stern shaft. On some large vessels, the stern tube shell may have reinforced structures such as ribs to enhance its load-bearing capacity.

Bearing section:

Bearings are installed inside the stern tube to support the stern shaft. There are various types of bearings, such as white alloy bearings, rubber bearings, etc. White alloy bearings are generally composed of cast iron shells and white alloys (such as Babbitt alloy) cast inside. The white alloy layer is in contact with the stern shaft, providing good wear resistance and anti friction properties; Rubber bearings are made of rubber material and use water as a lubricant, which has good elasticity and corrosion resistance, and can reduce the vibration and friction of the stern shaft.

Sealing device:

Both ends of the stern tube are usually equipped with sealing devices to prevent seawater from entering the ship. The types of sealing devices include stuffing box seals, mechanical seals, etc. Packing box sealing is achieved by filling the annular space between the stern shaft and stern tube with soft packing (such as oil immersed asbestos rope, rubber packing, etc.), and compressing the packing with a pressure cap to achieve sealing; Mechanical sealing is achieved through the high-precision combination of a dynamic ring and a static ring. The dynamic ring rotates with the stern shaft, while the static ring is fixed to the stern tube. The tight fit between the two prevents seawater from entering.

working principle

When the ship is sailing, the stern shaft rotates inside the stern tube. The bearings inside the stern tube provide support for the stern shaft, allowing it to rotate stably in precise positions. For example, in a white alloy bearing, an oil film is formed between the white alloy layer and the stern shaft (if it is an oil lubricated bearing), or in a rubber bearing, a water film is formed between the rubber and the stern shaft, which reduces the frictional resistance of the stern shaft. At the same time, the sealing devices at both ends of the stern tube play a role in preventing seawater from entering the ship during the rotation of the stern shaft. If it is a stuffing box seal, the packing tightly adheres to the stern shaft and stern tube under the pressure of the gland; If it is a mechanical seal, the high-precision combination of the dynamic and static rings ensures the sealing effect.

advantage

Good support and protection function: The stern tube provides stable support for the stern shaft, ensuring that the stern shaft can operate normally under various working conditions. At the same time, it also protects the stern shaft from erosion by seawater and collisions with external objects, extending the service life of the stern shaft.

Effective sealing of seawater: Its sealing device can effectively prevent seawater from entering the ship, which is crucial for the safety of the ship and the normal operation of equipment. During long-term navigation of ships, even in harsh sea conditions, the sealing performance can be reliably maintained.

Adapting to various types of stern shaft bearings: The structural design of the stern tube enables it to adapt to different types of stern shaft bearings, such as oil lubricated bearings, water lubricated bearings, etc. Suitable bearings are selected according to the specific needs and actual situation of the ship, improving the flexibility and adaptability of the ship's shaft system.

Disadvantages and countermeasures

The sealing device is prone to damage and aging: Due to long-term contact with seawater and friction generated during the rotation of the stern shaft, the stern tube sealing device is prone to damage and aging, leading to seawater leakage. The response measures include regular inspection of the wear and aging of the sealing device, and timely replacement of damaged components. At the same time, high-quality sealing materials and advanced sealing technologies such as double end mechanical seals can be used to improve the reliability of the seal.

Bearing wear and lubrication issues: The bearings inside the stern tube may experience wear during long-term rotation of the stern shaft, and if oil lubricated bearings are used, problems such as lubricant leakage or deterioration in oil quality may occur. For bearing wear, it is necessary to regularly check the degree of wear and replace the bearings in a timely manner; For oil lubrication issues, it is necessary to strengthen the management of lubricating oil, such as regularly checking the oil level and quality, and timely supplementing and replacing lubricating oil.

Application scenarios

Ship shaft system: The stern tube is an essential component in the shaft systems of various types of ships, including cargo ships, passenger ships, oil tankers, warships, etc. It is located at the stern of the ship and serves as a support and protective device for the stern shaft, ensuring the proper functioning of the ship's propulsion system.