One of the most important equipment of a vessel is its steering gear. It is designed to turn the ship to right (Starboard side) or left (Port side) while sailing. All ships are required to have the main steering gear and an auxiliary steering gear as backup. The main steering gear only works when the ship is in motion, not in stationary state. This is because the system uses a rudder, directly mounted behind the ships propeller. The rudder is controlled by the steering gear. When the bridge gives a signal to turn left, the rudder is moved to the left as well (seeing from the back), causing water forces to turn the vessel in the wanted direction.
Steering gear systems have minimum requirements to achieve certain safety levels. In example they are required to manoeuvre from 35 degrees port to 35 degrees starboard and visa-versa within 28 seconds, with the vessel sailing forwards at a steady maximum continuous rated shaft RPM. It also required to have an auxiliary system on the background in case the main system has failures.
Back in time it started with manually operated, mechanical steering gears. Strong sailors were required to operate this system. In the industrial era, in which steamships made their appear, this manually operated system was replaced by a mechanized system, which could be powered with steam pressure. Ships nowadays usually use one of these three systems:
- Fully hydraulic type
- Electro-hydraulic type
- Fully electric type
Each of these systems exist of three main parts:
- Control equipment
- Power unit
- Transmission to the rudder stock
Fully hydraulic types, the originator of the “modern system”, are working entirely by mechanical means. This type of systems is becoming more and more obsolete on vessels. Currently it’s the electro-hydraulic system dominating the applications. Electro-hydraulic systems work on hydraulic pressure created by pumps driven by an electric motor. This pressure can be led through the hosesto pressurize or depressurize certain pistons, causing the rudder to move to the left or the right.
The newcomer in steering gear systems is the fully electrical type, which does not use any fluid or pressure to operate. The rudder itself is fully depending on several electric motors which are mounted directly to the rudder.