Student Mauphuchuong8

Chapter 8 STEERING GEAR AND CONTROLLABLE PITCH PROPELLER I. Steering gear 1. Definition and classification of steering gear Steering gear is equipped in order to control the direction of ship's motion. Steering gear is classified into three types: -Mechanical -Electrical -Electro-hydraulic steering gears A steering gear system normally consists of: - A rudder that receives the stream of water forced by propeller and distributes to either port or starboard or both sides to control the direction of ship's motion. - Power (Amplifier) units that generate power to drive the actuator and then the rudder. - Actuator (servo) mechanisms that receive torque from the power units and transmit this torque to the rudder and turn the rudder. - A remote control system (telemotor or transducer system) that helps to control the steering gear(s) from the bridge and/or other control stations. 2. Basic requirements for steering gear system The steering gear system is very important. It affects the safety operation of the ship and even the life of crew on board. Regulation of SOLAS 74 and the major classification societies specify general requirements of a steering gear system that are summarized below: -Ships must have a main and an auxiliary steering gear, arranged so that the failure of one does not affect the operation of the other. An auxiliary steering gear need not be fitted when the main steering gear has two or more identical power units and is arranged such that after a single failure in its piping system or one of its power units, , steering capability can be maintained. - The main steering gear must be able to steer the ship at maximum ahead service speed and be capable at this speed, and at the ship's deepest service draught, of putting the rudder from 350 on one side to 300 on the other side in not more than 28 seconds. (This requests for ships with the rudderstock, excluding ice-strengthening allowance, is required to be over 120mm diameter at the tiller). -The auxiliary steering gear must be capable of being brought speedily into operation and be able to put the rudder over from 150 on one side to 150 on the other side in not more than 60 seconds with the ship at its deepest service draught and running ahead at the greater of one haft of the maximum service speed or 7 knots (This requests for ships with the rudderstock (excluding ice strengthening allowance) over 230mm diameter at the tiller). -It must be possible to bring into operation main and auxiliary steering gear power units from the navigating bridge. A power failure to any one of the steering gear power units or to its control system must result in an alarm on the navigating bridge and the power units must be arranged to restart automatically when power is restored. -Steering gear control must be provided both on the bridge and in the steering gear room for the main steering gear and the main steering gear comprised two or more identical power units there must be two independent control systems both operable from the bridge. Auxiliary steering gear control must be arranged in the steering gear room and where the auxiliary gear is power operated, control must also be arranged from the bridge and be independent of the main steering gear control system. I must be possible, from within the steering gear room, to disconnect any control system operable from the bridge from the steering gear it serves. It must be possible to bring the system into operation from the bridge. -Hydraulic power systems must be provided with arrangements to maintain the cleanliness of the hydraulic fluid. A low-level alarm must be fitted on each hydraulic reservoir to give an early audible and visual indication on the bridge and in the engine room. Power operated steering gears require a storage tank arranged so that the hydraulic systems can be readily recharged from a position within the steering gear compartment. The tank must be of sufficient capacity to recharge at least one power actuating system. -Where the rudderstock is required to be over 230mm at the tiller (excluding ice strengthening) an alternative power supply capable of providing power is provided automatically within 45 seconds. This must supply the power unit, its control system and the rudder angle indicator and can be provided either from the ships emergency power supply or an independent source of power. Its capacity shall be at least 30 minutes for ships of 10,000 Gt. and over and 10 minutes for other ships. Rudders There are many types of rudders: - unbalanced rudders - balanced rudders - active rudder

- In unbalanced rudder, the working area of the rudder that receives the flow of water forced by propeller is located entirely behind the rudderstock. Whenever the rudder is controlled to turn out of neutral position, there is force P of the water flow acting on the working area: and the steering power must be able to balance the force to keep the rudder at controlled angle.

- In balanced rudder the working area comprises two portions: one is located behind the rudder stock (F1) and the other before the rudder stock (F2). The application of balanced rudder can reduce steering power by introducing force P2 of water flow acting on area portion F2, which together with steering power balances force P1 of water stream acting on area portion F1.

- In active rudder, the rudder is equipped with an auxiliary propeller electrically operated. The operation of this propeller together with steering power on the rudderstock keeps the rudder at desired position against force P caused by water flow.

3 Steering gear types a- Mechanical steering gear In mechanical steering gears, power generated by steersman is transmitted mechanically to drive the rudderstock. Mechanical steering gears are only equipped for small boats which require very small steering power.

1.Wheel; 2. Wheel support ; 3. change direction gear; 4. Chain; 5. Connector; 6. Chain; 7. Connector 8. Reducing gear; 9. Rudder stock lever ; 10. Steering lever; 11. Spring link

Electric steering gears In electrical steering gear, electric motor is mechanically linked to rudder- stock by reduction gear. Generally, there are two methods to link the electric motor with the reduction gear: -flexible coupling -flexible clutch - In the flexible coupling the electric motor is linked to the reduction gear by a flexible coupling and the operation of the steering gear is simply controlled by starting or stopping the electric motor - In the flexible clutch the electric motor runs continuously throughout the sailing time, and the operation of the steering gear is controlled by engaging and disengaging the friction clutch. This prevents the electric motor from starting and stopping time to time with load. Nowadays, electric steering gears are rarely installed on board a ship.

Electro-hydraulic steering gears Actually, there are many types of electro-hydraulic steering gears. They can be driven by variable capacity or non-variable capacity pumps. They may be 2-ram type, 4-ram type, and rotary vane. - Electro- hydraulic steering gears equipped with variable capacity pump that controlling direction and speed of rudder by regulating supplied direction and capacity of pump. - Electro- hydraulic steering gears equipped with fixed capacity pump that controlling direction and speed of rudder by directional control valve.

Two ram electro- hydraulic steering gear with variable capacity pump

Four rams electric-hydraulic steering gear with variable capacity pump

Rotary vane

4. Steering gear control and remote control Normally, the steering gear is controlled from the bridge by a steering man (a steering wheel is provided) or by gyro-pilot (compass) hydraulically or electrically. The telemotor itself employs a 'master and slave' principle. The transmitter is situated on the bridge and the receiver at the steering gear unit. Mechanical movement is transduced hydraulically or electrically for distance telemetering and then transduced back again to mechanical movement. Electric remote control systems are commonly used because of their inherent simplicity and reliability and they are adaptable to the control of any type of steering gear. - In case of hydraulic steering gear with variable capacity pump, pump output and therefore rudder movement is controlled by a floating lever. In fact, three arrangements of floating lever are applied as follows. The control signal impacts the point A. Point B (hunting point) is connected to the rudder-stock through a lever with buffer spring. Point C is linked to the hydraulic pump control mechanism

Three arrangements of the floating lever

Hydraulic steering gear with variable capacity pump

Hydraulic steering gear with variable capacity pump - In case of hydraulic steering gear with fixed capacity pump, the flow direction from the hydraulic pump to actuator is controlled by directional control valves (solenoid valve) and therefore rudder movement is carried out.

Hydraulic steering gear with fixed capacity pump

● Control of steering gear: The steering gear can be controlled (operated) by the following methods assuring correct and easy handling and changing: - Automatic steering by remote control system in wheelhouse (Auto. Pilot control from the bridge) - Normal steering. - Hand steering by remote control system in wheelhouse - Normal steering: + Follow up control from the bridge + Non-follow up control from the bridge . - Local steering in the steering gear room - Engine side operation with the control lever of the main hydraulic pump (emergency steering).

Auto-Pilot block diagram

5. Steering gear operation and maintenance - Normally, the steering gear should be thoroughly checked and tested within 12 hours before arrival and departure. These tests should include testing of power unit and control system failure alarms, the emergency power supply and automatic isolating arrangements. - Every three months an emergency steering drill should be carried out, including direct control from within the steering gear room. At the same time the use of the communication procedure and communication system between steering gear room and the bridge should be practiced. ● For electric steering gear, following items should be checked to ensure good condition of the steering gear. - Oil level in the housing of the transmission gears. - Insulation of electric motor and devices - Operation of mechanical limiters and cut-off. - The operation of the steering gear at different control stations - Temperature of electric motor bearings, transmission gears. - Noise and vibration of transmission gears when operation. ● For hydraulic steering gear, keeping hydraulic oil free from dust and impurities is the most important thing to ensure good conditions of the steering gear.

II. Variable pitch propeller 1. Introduce of variable pitch propeller Variable pitch propeller is kind of propeller that it can control the pitch of propeller to control the load of main engine when the ship needs to change the speed during maneuvering or bad weather. 2. Methods for controlling propeller pitch: There are 4 common methods to control the propeller pitch as follows

3. Structure of controllable pitch propeller There are three main parts in CPP -Propeller blades can be turned around their axis -The pitch control mechanism. -Propeller hub

Structure of variable pitch propeller

4. Variable pitch propeller system. Hydraulic system, normally is used to turn blades of the propeller. The remote control system for it may be a electro- hydraulic system or pneumatic system. In electro-hydraulic remote control system: the control signal from the Bridge or the control room is transmitted to directional control valves. All alarm signal and indicating signal are electric signal. In pneumatic remote control system: All signal for control and indication are pneumatic signal. Electric signal is used for alarm.

Electro-hydraulic remote control system for vriable pitch propeller 1.Control hand; 2. Indicator; 3. Directional control valve; 4. Auxiliary cylinder; 5. Sensor; 6. Directional control valve; 7. Servo cylinder 8. Propeller; 9. Connecting lever; 10. Reducing valve; 11. Relief valve 12 . Safety valve; 13. Filter 14. Hyd. Pump; 15 cooler 16. tank

Questions. 1. State function and duty of steering gear and requirements of steering gear on board ships. 2. State the methods used to control the steering gear. Draw and explain the block diagram for auto steering. 3. State function of parts and explain operating principle of electrical hydraulic steering gear using the fixed capacity pump. 4. Put the name of parts, state function of those parts and explain operating principle of two ram electrical hydraulic steering gear. 5. Put the name of parts, state function of those parts and explain operating principle of electrical hydraulic steering gear using variable capacity pump. 6. Give the concepts of controllable pitch propeller. 7. Explain the principle of operation of an electro-hydraulic remote control system for CPP.

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