Definition and Function

Definition: Marine rudder blade is a key component of the ship's rudder system, which is a large flat or streamlined structure installed at the end of the rudder stock. The main function of the rudder blade is to change its angle in the water, generate lateral force, and thus alter the course of the ship.

Function:

Steering function: When the rudder blade rotates a certain angle, the water flow exerts lateral force on the rudder blade. This force generates a rotational moment around the center of gravity of the ship, causing it to turn. For example, when the rudder blade rotates to the port side, the water flow acts on the right side of the rudder blade, generating a lateral force to the left, pushing the ship to turn to the left.

Maintain heading function: When the ship deviates from its heading due to external disturbances such as wind, waves, and water currents, adjusting the angle of the rudder blades can correct the heading and keep the ship on the predetermined route.

Structural composition

Shell part:

Material selection: The rudder blade shell is usually welded from steel plates. In order to reduce weight and enhance structural strength, some high-performance ships may use high-strength alloy steel or composite materials for their rudder blades. The thickness of the steel plate is determined based on factors such as the size of the rudder blades and the type of vessel, generally ranging from a few millimeters to several tens of millimeters.

Shape design: The shape of the rudder blades is mostly streamlined to reduce resistance when moving in water. Common shapes include flat rudder blades, streamlined rudder blades, and flap rudder blades. Flat rudder blade structure is simple and cost-effective; Streamlined rudder blades have better fluid performance and can effectively reduce drag; Flap rudder blades are equipped with movable flaps at the trailing edge of the main rudder blade to further improve rudder efficiency and enhance ship maneuverability.

Internal structure:

Strengthening ribs and skeleton: In order to enhance the strength and stiffness of the rudder blade, internal reinforcement ribs and skeleton are usually provided. Reinforcing bars are generally made of flat steel or angle steel, welded inside the rudder blade at a certain spacing and layout. The skeleton is composed of criss crossing steel beams, forming a sturdy frame structure that can withstand the enormous pressure of water flow on the rudder blades.

Filling materials (some rudder blades have): some rudder blades will be filled with foam plastic, wood or other light materials to increase the buoyancy of rudder blades, reduce the burden of rudder stock, and provide a certain reserve buoyancy when the rudder blades are partially damaged, so as to prevent the rudder blades from sinking.

working principle

When the rudder blade is in the neutral position, the water flow flows relatively smoothly through the rudder blade, and the ship maintains straight sailing. When the servo drives the rudder blades to rotate a certain angle, the direction of water flow is no longer parallel to the surface of the rudder blades. According to the principles of fluid mechanics, water flow creates a pressure difference on both sides of the rudder blade, resulting in a lateral force perpendicular to the plane of the rudder blade. This lateral force generates a rotational moment on the center of gravity of the ship, causing it to rotate around the center of gravity and achieve turning. For example, during the rotation of the rudder blade, the pressure on the upstream side of the rudder blade increases, while the pressure on the downstream side decreases. The pressure difference increases with the increase of the rudder blade angle until it reaches a large rudder angle (usually around 35 ° -40 °), at which point the rudder effect also reaches a large value.

advantage

Efficient steering: By designing the shape and size of the rudder blades reasonably, sufficient lateral force can be generated at a smaller rudder angle to achieve efficient steering of the ship. This helps ships to maneuver flexibly in complex waters such as narrow waterways and ports.

Multiple shapes to meet different needs: Different shapes of rudder blades, such as flat rudder blades, are suitable for small ships or ships with low maneuverability requirements, while streamlined and flap rudder blades are suitable for large ships and high-performance ships, providing suitable maneuverability according to the type, purpose, and navigation conditions of the ship.

Reliable structural strength: Through internal reinforcement ribs and skeleton structure, the rudder blades can withstand the enormous pressure generated by water flow in various sea conditions, ensuring the safety and reliability of ship maneuvering.

Disadvantages and countermeasures

Vulnerable risk of damage: Due to the rudder blades being located at the stern of the vessel and exposed to water, they are susceptible to damage from floating objects, seawater corrosion, and other factors. The response measures include installing protective devices such as rubber fenders at vulnerable parts such as the leading edge of the rudder blades; Regularly inspect the surface condition of the rudder blades and promptly repair any corrosion, deformation, or other issues found; Consider increasing the impact resistance of the rudder blades during design, such as using thicker shell materials or reinforced structures.

Resistance issue (partial rudder blades): Some poorly shaped rudder blades may increase the resistance of ship navigation and reduce the propulsion efficiency of the ship. For this situation, it is possible to optimize the shape design of the rudder blades and use advanced fluid dynamics simulation techniques to design streamlined or high-performance rudder blades that are more in line with fluid dynamics principles, reducing drag; At the same time, during the navigation of the ship, the angle of the rudder blades should be reasonably controlled to avoid unnecessary increase in resistance.

Application scenarios

All types of ships, whether they are large ocean going cargo ships, oil tankers, container ships, small and medium-sized passenger ships, fishing boats, speedboats, etc., require the installation of rudder blades to achieve steering and heading control of the ship. Different types of ships choose appropriate rudder blade types and sizes based on their own characteristics and navigation requirements to meet the requirements of maneuverability.