Definition and Function

The stern nut is a key component in the ship's shaft system, installed at the end of the stern shaft, with the main function of firmly fixing the propeller to the stern shaft. During the navigation of a ship, the propeller is subjected to tremendous thrust and torque. The stern nut ensures that the propeller does not loosen through pre tightening force, ensuring the reliability of the connection between the propeller and the stern shaft. This enables the propeller to effectively convert the power of the main engine into the propulsion force of the ship.

Structural characteristics

Nut body:

The stern shaft nut is usually a large nut, and its size depends on factors such as the diameter of the stern shaft and the propulsion power of the vessel. It is generally made of high-strength alloy steel, such as 42CrMo, which has high strength and toughness and can withstand the huge axial force generated by the propeller during operation. The thread accuracy of the nut is required to be high to ensure a tight fit with the thread at the end of the stern shaft and prevent loosening.

Anti loosening device:

In order to prevent the stern shaft nut from loosening during ship vibration and propeller rotation, anti loosening devices are usually equipped. Common anti loosening methods include split pins, stop washers, double nuts, etc. Open mouth pin is a simple and effective anti loosening method, which inserts the open mouth pin into the hole on the nut and stern shaft to prevent the nut from rotating; The stop washer, through its special shape and structure, clamps the nut and stern shaft to prevent the nut from loosening; Double nuts utilize the friction and mutual restraint between two nuts to achieve anti loosening.

working principle

When installing the propeller and stern shaft nut, first install the propeller at the end of the stern shaft, and then tighten the stern shaft nut onto the thread of the stern shaft. During the tightening process, sufficient pre tightening force is applied using specialized tools such as hydraulic tensioners to tightly press the nut against the propeller. This preload force should be sufficient to resist the axial force generated by the propeller during operation, preventing the propeller from loosening. For example, when a ship is moving forward, the water thrust acting on the propeller will attempt to move the propeller forward relative to the stern shaft, while the preload force of the stern shaft nut can prevent this movement. At the same time, the anti loosening device plays a role in ensuring that the stern shaft nut will not loosen on its own during long-term vibration and rotation.

advantage

High connection reliability: The stern shaft nut can firmly fix the propeller on the stern shaft through high pre tightening force and effective anti loosening device, ensuring the stability of the connection between the propeller and the stern shaft. Under various working conditions of the ship, such as different sea conditions, changes in engine speed, etc., the propeller can be ensured not to loosen, thereby ensuring the safety of the ship's propulsion.

Simple and effective structure: Its basic structure is a nut with an anti loosening device, which is relatively simple. This simple structure is easy to manufacture, install, and maintain, and can effectively fulfill its function of fixing propellers in ship shaft systems.

Disadvantages and countermeasures

Thread wear issue: Due to the threaded connection between the stern nut and the stern shaft, the threads are prone to wear during long-term use, especially when the propeller rotates frequently and the ship vibrates. The response measures include designing the parameters of the thread reasonably during the design phase, such as pitch, profile, etc., to improve the wear resistance of the thread; During use, regularly check the wear of the threads. When the wear exceeds a certain limit, replace the nut or repair the thread of the stern shaft in a timely manner.

Risk of failure of anti loosening device: If the anti loosening device is installed improperly or used for a long time in harsh environments, it may fail. For example, a split pin may break due to corrosion, and a stop washer may deform. The response measures are to regularly check the effectiveness of the anti loosening device, replace damaged anti loosening devices in a timely manner, and strictly follow the operating procedures during installation to ensure the correct installation of the anti loosening device.

Application scenarios

Ship propulsion system: The stern shaft nut is an essential component in the shaft system of all ships propelled by propellers, including cargo ships, passenger ships, oil tankers, warships, etc. It is used to fix the propeller and is a key link in the ship's power transmission chain, ensuring that the ship can obtain stable propulsion.