With advancement in technology, the ship transportation has evolved from small wooden boats to very large and advanced ships, and the ship control system has also evolved at the same pace. In today’s scenario where many big players are developing autonomous ship, that doesn’t require any human onboard to run is an example of our achievement in control engineering. These ships can be controlled from thousands of miles with just finger click. But this evolution has taken many years to achieve this.
The main aim of developing control system is to run the system on its on i.e without human interference. For example the viscosity control of fuel on board. A set value is defined by a human(watchkeeper), after this, the viscosity controller will control the this with its own control system. It will take the feed (present viscosity of fuel) and compares with the set value. On the basis of this difference, the corrective action will be taken by the system. The main aim of a control system is to provide decision making capability to the system. This will not only increase the efficiency of the system but also speed up the process.
These ship system can be of mechanical, electrical or fluid types. A full mechanical type control systems are obsolete now, they can be used with a mechanical or fluid type system. Electrical and pneumatic types of control systems are a very common type control system for any automation. Earlier pneumatic and hydraulic systems were used extensively, but now most of them are replaced by an electrical system with sensors and controllers. All these systems have some advantages and disadvantages over each other. So, let’s discuss it.
Pneumatic Ship Control System
In this system, air pressure or flow is used as a measuring unit. And the corrective command also involves air pressure. For example, auto backwash filters where the pressure difference of incoming and outgoing oil is measured in term of air pressure. When air pressure will increase because of filter getting choked and at a defined value filter will backflush with help of air.
Advantages of Pneumatic Ship Control System:
- This is not affected by ship’s power supply variations for short term.
- It requires a low cost of installation.
- No heat generated and hence no risk of fire.
- The simplicity of the components and no complex structure.
- Actuators are cheaper and accurate than electric systems.
- It involves only simple control air piping system.
Disadvantages of Pneumatic Ship Control System:
- It requires at least an air compressor and associated air systems.
- The copper piping is vulnerable to damage very easily.
- A clean, dry and oil free supply of good quality air is essential for satisfactory operation of
- Good quality air requires driers, filters with drains, etc. which increases maintenance.
- It may have transmission lags in large systems.
- The Pipe-couplings can give rise to leaks in certain ambient conditions.
- It has some potential noise.
Hydraulic Ship Control System:
In this system, fluids are used as a measuring unit. The earlier hydraulic control system was widely used in ships steering system. The fluid varies from system to system.
Advantages of Hydraulic Ship Control System:
- This system has the high horsepower-to-weight ratio.
- It’s reliable to operate.
- The leaks in this systems are easier to find.
- It always maintains constant torque and force.
- The hydraulic power can be transmitted over long distances.
- The motion reversal in the hydraulic system is fast.
- It is capable of handling strong, heavy loads, shock forces.
- It requires less energy to operate.
- The overall wear because of oil lubrication is less.
- In any case, it does not generate sparks.
- It is capable of smooth operation for lifting and movement of loads.
- It can operate in hot environments.
Disadvantages of Hydraulic Ship Control System:
- It involves a more expensive initial installation than a pneumatic system.
- The response is slower motion than pneumatic.
- It is a noisier system.
- It involves the risk of contamination.
- The leakage of the oil is a big problem.
- This system requires more maintenance.
- It involves heavier components and parts.
- Few hydraulic fluids dangerous to humans and, not environment-friendly.
Electrical Ship Control System:
It involves a complex system of cables and controller. The widely use controller in PID control. It is the most accurate controller in the industry. It is been used in many systems e.g. Boiler level controller, turbine ship control etc. One of the latest development includes HART Control, in which all controllers will be wireless and system setting is remotely controlled.
Advantages of Electrical Ship Control System:
- For this system, no air compressor and associated machinery required.
- It is having high efficiency since there are no leakages.
- It is very little affected by normal temperature variations.
- This system is having a very accurate and quick response.
- It involves electric cables, which are cheap and easy to lay.
- In this system, no entrainment or contamination in the control medium
Disadvantages of Electrical Ship Control System:
- The system requires an uninterrupted power supply with no voltage fluctuations.
- This involves complex networks
- It requires standby batteries in case of power failure.
- If there is a risk of fire due to overheating. Expensive intrinsically safe / explosion proof
equipment may be required.
- Difficult maintenance and test kit requirements
- Moisture may cause damage to the system.
- The damage readily occurs in the event of a fire.
A ship control system is always involved in complexity with all above system. Main engine manoeuvring system involves pneumatic, electrical system. Earlier pneumatic control lines run from bridge to the main engine for start, stop and speed control. And from the main engine to bridge as a feedback system. But with advancement in electrical sensors and controllers, most of them have been replaced by the electrical system. One of the means of communication from the bridge to the engine room is telegraph, which is electrically connected with each other with solenoid valves for each movement. And all these commands are connected to main engine speed control system with help of pneumatic and electrical signals.
In latest electronically controlled engines camshaft of the engine is replaced by solenoid valves which control the engines with help of electrical signal. All these improvements not only increased the reliability of engines but also results in less maintenance of the engine and ultimately reducing the operating cost of the ship.