In response to a signal from the bridge, the steering gear moves the rudder. The propeller provides water thrust to the rudder, which guides the vessel.
Table of Contents
Important Parts of the Ship Steering Gear System
- Instruments of control
- Power unit
- Transmission to the rudder stock.
The control equipment transmits a signal from the bridge to the steering flat, where it is received and used to activate the power unit and transmission system until the necessary rudder angle is achieved. The power unit delivers the force to move the rudder to the proper angle when it is needed and with quick impact. The transmission system (steering gear) is the mechanism that allows the rudder to move.
Hydraulic control equipment (sometimes known as a “Tele-motor”) or electric-electronic control equipment are two types of control equipment. The power unit itself might be hydraulic or electrically powered.
There are two types of hydraulically powered transmission units or steering gears:
Steering Gear Operation
Let’s look at how these steering motions happen in real time, automatically, and appropriately. Let’s look at a 5-degree port movement.
Two rams, a pump, and a motor make up the two-ram hydraulic steering gear. Pump is a unidirectional, continuous-running, constant-speed pump that can have reverse flow and changeable rate of flow.
When the pump stroke lever (PSL) is pressed into the pump, it causes pressure in the LHS pipes and de-pressures in the RHS pipes. And if the PSL is drawn out, vice-versa is the case. The pump will not operate if the PSL is just in the centre (i.e. the position indicated by “O”). The pump is at the zero-pumping position here and the oil will be just trapped within the LHS and RHS ram cylinders.
When the wheelhouse sends a 5 degree port signal, the tele-motor receiver cylinder in the steering flat moves to the left equivalent to the 5 degree port. L1 (fulcrumed in the centre) will assume the location indicated by the L1 centre line. Lever L2 will rotate around point (F) and take the position indicated by the L2 centre line.
PSL will be disturbed (because to the fact that it is riding on lever L2) and forced into the pump. Pump will begin pulling from RHS cylinder and pumping into LHS cylinder.
From left to right, the Rams will slide. The rudder will begin to move closer to the port. The lever L3 will be pulled to the left as the rudder goes to port (port side). The rudder will continue to move towards port until the lever L3 pulls in the lever L2 from the L2 centre line to the L2 new centre line (around point E) and the PSL returns to zero pumping (o). Because the pump is no longer working, the rudder will be hydraulically locked at 5 degrees P.
The helm will spring back to mid-ship position when you release the helm at the wheelhouse, and the receiver cylinder in the steering flat will spring back to mid-ship position. Lever L1 will move from the L1 centre line to the L1 position and the pump will start pumping again, this time into the starboard cylinder, until the rudder returns to the mid-ship position.
4- Ram Electro- Hydraulic Steering Gear.
A 4-ram hydraulic steering gear is required on some ships or is given as standard equipment. Instead of two rams, we have four rams here. Such a solution allows us to isolate any leaking component from the system, guaranteeing that steering power is available at all times.
Relief Valves on Hydraulic Circuit
Both sides of the ram cylinders are full with oil, and the rudder is hydraulically locked, at any position of the rudder. As a result, even if external factors such as wave pressure, etc. try to move the rudder, it will remain in place. Oil pressure in the appropriate ram cylinder will rise as the rudder moves. The rudder stock will, however, twist during such a propensity. (The rudder is forced to move from the bottom end of the rudder stock, while the locked rams prevent it from moving from the top end.
Now, if this twisting torque is excessive the rudder stock may twist or even shear off. To prevent shearing off, and other damages, a set of relief valves are incorporated in the hydraulic system.
Consider a wave pushing the rudder to the port side from its mid-ship position. The wave force will push the starboard ram into the starboard cylinder, causing hydraulic pressure to build up on the RHS. If the wave force is high enough, the pressure will build up to the point where the relief valve will lift up, releasing pressure from the RHS to the LHS. Oil will seep from the RHS to the LHS, enabling the rudder to sag. The rudder goes closer to the port, and the wave moves on. Simultaneously, the pump stroke lever is upset, and the pump begins to pump, restoring the rudder to its original position (in this case the mid-ship position.
Electric Steering Gear
This steering gear has the advantage over the others in that all connections from the bridge to the steering engine compartment consists of electric cables; no telemotor or mechanical control being needed. The rudder stock is moved by electric rudder motor, through worm, worm- wheel, pinion and quadrant. The quadrant moves simultaneously with the pinion, storing energy in buffer springs. The buffer springs will then release stored movement slowly to the tiller arm, which in turn moves the rudder.
The electric machinery involved are rudder motor, generator for supplying power to the motor, motor for the electric generator, generator exciter and rheostat for control.
Rotary Vane Steering Gear
It consists of a rotor that is taper fit on the rudder stock and keyed to it, and a stator with a greater internal diameter than the rotor’s exterior diameter to produce an annular gap between them, with the stator firmly fastened to the ship’s structure by anchor bolts to prevent it from turning.
Until the rudder is in the desired position, a variable delivery pump delivers to one side and receives from the other. The feedback lever L3 brings the pump to neutral (zero pumping position) at this moment, and the rudder becomes hydraulically locked.
The rotary vane type costs less to provide the same torque on the rudder stock as the 4 ram hydraulic steering gear, is lower in weight, takes up less room, and requires less maintenance.
Variable delivery pump
This pump, which is also known as the Hele-shaw pump, is made up of a fixed shaft and a rotating cylinder body. The cylinder body is surrounded by an odd number of cylinders. Each cylinder is equipped with a plunger that is connected to slippers that run in annular grooves inside two circular rings on either side of the plungers. During one spin, just one cylinder of the cylinder plunger assembly is displayed in four distinct positions.
Depending on the location of the circular ring, the plunger may move in and out in addition to spinning with the cylinder. The plungers will move if the centre of the circular ring is concentric with the centre of the stationary shaft, as represented by O, the plungers will have no in and out movement. If circular is moved left, the center of the ring is at A, the plungers will have movements outward when passing from 1 to 2 and inward when passing from 3 to 4.
As a result, the plunger will work like a pump, pulling oil from the top (T) and pushing it into the bottom (B) of the stationary shaft’s oil chamber.
The pump is a variable delivery pump because the stroke of the plungers may be adjusted by changing the eccentricity of the circular ring.
An electric motor rotates the cylinder body at a steady speed and direction. To provide greater hydraulic flow and improve pump balance, an odd number of cylinders, generally seven or nine, is given.
Rules Pertaining to Steering Gears
- All vessels must have effective power-operated main and auxiliary steering gear. If the main gear has double power units and connections up to the rudder stock, an auxiliary gear is not necessary.
- The main steering gear must be capable of steering the ship at maximum forward service speed and putting the rudder from 35 degrees on one side to 30 degrees on the other side in no more than 28 seconds at this speed and at the ship’s deepest draught.
- The vessel must be equipped with the ability to steer from an aft location.
- Unless the working tiller is of unique design and strength, two tillers (or their equivalent) are necessary.
- Power-operated gears must be equipped with a shock-absorbent device.
- All lead connections, whether steam, hydraulic, or electric, should be separate from the gear. Electric lines and fuses should be able to withstand a 100 per cent overload.
- To avoid danger to workers, moving portions of steering gears should be guarded.
- Non-freezing fluid should be used in hydraulic systems. Wooden gratings should be installed on the steering room floors to allow for simple personnel mobility in the event of an oil leak.
- The steering position must provide a clear vision, and the wheel, tell-tale indications, and rudder movement must all correlate to the precise amount and direction for the ship’s heading.
- Operating trials on steering gears should be conducted to determine the degree of action time, angle of heel at various speeds, and other factors.
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