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
