Working [Video Lesson]

The main control of the steering operations is given from the helm of any ship, similar to an automobile where the entire control of the vehicle’s “steer-ability” rests on the steering wheel of the driver.

 

The ‘control force’ for turning is triggered off from the wheel at the helm, which reaches the steering gear system.

 

Video Lesson:

 

The steering gear system generates a torsional force at a certain scale which is then, in turn, transmitted to the rudder stock that turns the rudder. The intermediate steering systems of a modern-day ship can be multifarious with each small component having its own unique function.

 

We omit to discuss each and every such component in detail. 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:

  • Radial piston type (Hele-Shaw)
  • Axial Piston type (Swashplate)

Ram Type Steering Gear System

The ram-type steering gear is one of the most commonly used steering gear construction and is quite expensive construction. The basic principle is the same as that of a hydraulically-driven motor engine or lift.

 

There are four hydraulic cylinders attached to the two arms of the actuator disc, on both sides. These cylinders are directly coupled to electrically driven hydraulic pumps which generate hydraulic pressure through pipes.

 

ram-type-steering-gear

 

This hydraulic pressure field present in the pumps imparts motion to the hydraulic cylinders, which in turn corresponds with the actuator to act upon the rudder stock.

 

As we know, rudder stock is an indispensable part of the entire steering gear arrangement of ships and dictates the exact behaviour of the rudder response. The sense of turning the rudder is guided by the action of the hydraulic pump.

Rotary Vane Steering Gear

In the rotary vane steering gear, there is a fixed housing in which two vanes rotate. The housing along with the vanes form four chambers. The physics behind its operation is similar to the ram type with a small difference. When chambers A and C are pressurized, there is an anticlockwise rotation of the vanes.

 

A and C are connected to the discharge side of the pump while chambers B and D are connected to the suction side of the pump. Similarly, when clockwise rotation is required, B and D are connected to the discharge side of the pump while A and C are connected to the suction side of the pump. As above, this is also operated by specialized control valves.

 

Rotary Vane Steering gear

 

Thus, differential pressurization of the chambers causes rotational moments in the vane. A rotary vane type arrangement is used when the pressure requirement is 60 to 100 bar for producing the required torque. This is the main advantage of rotary vane type steering gear, requiring lesser hydraulic pressure and thus power for producing the same amount of torque as ram type. There are 3 fixed and 3 moving vanes, which can make rudder angles up to 70 degrees, i.e. 35 degrees on each side.

 

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