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Knowledge of the Ship Main Equipment Part (IV)

Knowledge of the Ship Main Equipment Part (IV)

 2. Rudder

Rudder is the main equipment of controlling ship, to maintain and heading direction during the voyage. It is mainly composed of rudder gear, servo, steering device and maneuvering gear and other equipment, they are respectively installed the bridge, servo room and at the bottom of stern. Rudder operation is by the pilot to turn the steering wheel or the steering handle, start the hydraulic or electric power maneuvering gear to control servo, to make the rudder forward, reverse, or stop.

(1). Rudder Gear

Rudder and bearing components are collectively referred to as the rudder gear. Rudder is the slab structure with a rotating flat profile or streamlined profile at the end of the ship; it is vertically submerged in the water. When the ship is moving, rudder is turned around a angle, meanwhile, due to the relative motion of the discharge water of propeller and rudder, there will be water pressure on the surface of the rudder, the water pressure is perpendicular to the component force of the ship longitudinal profile, it is the torque that makes a ship around the center of gravity to rotate. When ship is forward, left rudder Angle makes the boat to the left, right rudder Angle makes the boat to the right. Within a certain range, the torque is increased as the rudder Angle’s increasing, usually, the full rudder’s Angle is 350, the water pressure on the rudder is related to the relative speed of rudder Angle and water, but also is directly proportional to the area of the rudder.

There are many different kinds of rudder; according to the different section shape of the rudder, it can be divided into flat rudder and aerodynamic rudder, as shown in figure 1-32; According to the rudder axis location, it can be divided into unbalanced rudder, balanced rudder and half balanced rudder. The section shape of the flat rudder blade is flat, the rudder resistance is bigger, and it is mainly used for small boat. Aerodynamic rudder blade profile is streamlined, the rudder is made into hollow watertight; on the one hand, it can reduce the weight of the rudder, on the other hand, it also can reduce the carrier pressure on the rudder. The small resistance, high strength and good steering, can improve the stability of the rudder. The structure is complicated, but is widely applied.

(2). Servo

With the increasing of the speed and the registered tonnage of the ship, effects on the torque of steering are also greatly increased, so it must provide steering power with the aid of servo. Servo is a mechanical device, which used to generate steering torque face to make the rudder deflection. Now, used on the ship is electric servo and hydraulic servo. Electric rudder consists of motor, worm gear, worm, quadrant, tiller, etc. the simple structure, convenient operation and reliable work are suitable for small and medium-sized ships. Hydraulic servo can be divided into piston hydraulic servo and vane hydraulic servo, is mainly composed of motor, pump and pipeline such mechanical components, has the advantages of small volume, light weight, large torque, transmission shift with low noise and easy management, large ships are using this servo.

(3). Steering Gear

Servo makes the rudder blade deflection, and through the steering gear, plays a supplementary role on transmission torque between the servo and rudder. The major types: tiller typed steering gear and rudder fan typed steering gear.

(4). Maneuvering Gear

The device is the generic term of the package unit, which transports the steering instructions from bridge to the servo, and then makes the servo work according to the requirement of the floorboard. There are two kinds of modes of transmission: one is electric drive, the other is hydraulic drive. With the principle of liquid cannot be compressed, its flow and flow rate, hydraulic maneuvering gear can be artificially controlled to drive. But the device is relatively heavy to manipulate, and the response is slow, become obsolete gradually. Electric maneuvering gear is to drive by electricity signal, has the advantages of convenient operation and high sensitivity. At present, the ship is using this device; it is advantageous for the ship to realize the automatic steering.

About the ship using electric maneuvering gear, there are two sets of independent steering system, when a rudder system failure occurs, immediately, another set of steering system would start. The two systems are known as follow-up steering system (main maneuvering gear) and the handle steering system (auxiliary maneuvering gear).In addition, the ship still need to configure the emergency maneuvering gear, when all failure of the maneuvering gear system occur, using the emergency maneuvering gear in the servo room with  the bridge and servo room communication mode.

Automatic steering control device, referred to as autopilot, is developed on the basis of follow-up steering, a fully automatic control way of steering. It is based on the comparison of gyro compass heading signal and specified course to control the operation system, automatically keep the ship on the specified course. Due to the high sensitivity and accuracy of autopilot, instead of manual steering, it relative improves speed and lightens the load of the steersman. The merchant ships are equipped with autopilot, when navigation direction is stable and there is no other boat in the navigation area, can be changed to steering autopilot.