1.2 Steering gear system
Steering Gear integrated with the rudder system defines the complete ‘turning mechanism’ mandatory for each and every ship irrespective of size, type and operation. The steering gear system has been an indispensable part of the ship’s machinery since the advent of the very early ships, which were operated by hand.The efficiency of the performance of steering gear depends on some main aspects. These basic requirements to be invariably met by all steering gears are guided by rules set by classification societies. They can be briefly outlined as:
- As per standard requirements, the steering gear should be capable of steering the ship from 35 degrees port to 35 degrees starboard and vice-versa with the vessel plying forwards at a steady head-on speed for maximum continuous rated shaft rpm. and summer load waterline within a time frame of a maximum of 28 seconds
- With one of the power units inoperative, the rudder shall be capable of turning 15 degrees port to 15 degrees starboard (and vice-versa) within a time frame of 1 minute with the vessel moving at half its rated maximum speed of 7 knots (whichever is greater) at summer load line
- The major power units and the control systems are to be duplicated so that if one of them fails, the other can easily substitute for them as standby
- Emergency Power Supply: The steering gear system is to be provided with an additional power unit (hydraulic pump etc.) connected to the emergency power supply from the Emergency Generator, which shall be capable of turning the rudder from 15 degrees from one side to another side within 60 seconds with the vessel moving at a maximum service speed or 7 knots, whichever is greater. As ships continued to grow in size and became faster, modern systems easing human effort were incorporated. Basically, there are two types of commonly used steering gear systems present:
- Hydraulic
- Electro-hydraulic type
Though the system has undergone some major evolution, the basic physics of operation remains the same.
The rudder system consists of the following:
- Rudder actuators
- Power units
- Other auxiliary equipment needed to apply turn the rudder by applying torque
- Hydraulic pumps and valves
In hydraulic and electro-hydraulic systems, hydraulic pressure is developed by hydraulic pumps which are mainly driven by electric motors (electro-hydraulic systems) or sometimes through purely mechanical means (hydraulic systems). In hydraulic and electro-hydraulic systems, hydraulic pressure is developed by hydraulic pumps which are mainly driven by electric motors (electro-hydraulic systems) or sometimes through purely mechanical means (hydraulic systems). However, mainly advanced electro-hydraulic systems are predominant in ships nowadays. These hydraulic pumps play a crucial role in generating the required pressure to create motions in the steering gear which can trigger the necessary rotary moments in the rudder system.
These pumps are basically of two major types:
Actuators mediate the coordination between the generated hydraulic pressure from pumps (driven electrically, of course) and the rudder stock by converting it into a mechanical force creating a turning moment for the rudder. Actuators are now mainly electrically driven by power units.
These actuators, in turn, can be of two types:
The types of actuator systems depict the types of steering gears present on ships, which are also segregated as Ram type and Rotary Vane type arrangements accordingly.