Ship Systems: A focussed overview
Introduction
Ever visited a ship and wondered… “Man, what is up with all these pipes everywhere?” A maritime vessel may be very complex from the outside (or from the inside as well ;) ). Just like a human body has dedicated systems for every function, a ship too has various ‘systems’ consisting of a plethora of subsystems, and individual parts. Further, some of these systems can be interdependent on each other while the rest can be standalone style, but provisions are also made for contingencies in emergencies. This comprehensive guide delves into the essential systems onboard a typical merchant ship. Broadly, they can be categorised into propulsion and power, steering, navigation, supply and service, and safety systems. Now, these are not the only categories, rather, there are many more if we take a deeper look. But the systems mentioned in this guide are essentially engineering systems that help the basic functioning of the ship.
Propulsion & Power
To begin with, we need a means of moving forward and generating electricity to run many machines onboard. Every ship has some form of propulsion system to allow it to overcome water resistance and move in a particular direction. My article on ‘propulsion systems’ explains the various types of propulsion systems. Please do read it! The engine and drivetrain form the core of a ship’s propulsion system. The engine provides the necessary power for propulsion, and various types of engines are used in the maritime industry. Diesel engines are the most widely used due to their efficiency and reliability. Some warships employ gas turbines for high-speed operations. Recently, the maritime industry has been shifting towards hybrid and electric propulsion systems, with electric motors expected to play a significant role in the future. With more stringent norms for emission control imposed by the International Maritime Organization under their MARPOL convention, shipowners, builders and engine manufacturers are finding new ways to generate cleaner energy for large vessels without a loss in performance. The power generated by the prime mover (engine/electric motor) is transferred via a drivetrain, typically consisting of a shaft and propeller arrangement. This traditional and trusted method is used in almost all vessels. Propellers are complex engineering products that have been studied and perfected by naval architects for decades. Variable and fixed pitch types are available depending on the application. Some high-speed vessels use pumpjet drives with bucket reversers, offering enhanced manoeuvrability and efficiency. Gearboxes can also be seen between the engine and shaft inputs to raise the torque delivery. Ships generate electricity using electric generators powered by prime movers such as gas turbines, or diesel engines. The amount of power generated can vary anywhere from hundreds of kilowatts to several megawatts for large vessels. Additionally, a shaft output can be taken from the main drive to generate power. However, this approach reduces propulsive power and halts electricity generation when the engine is off. When the vessel is docked at a port or drydoked, electrical power is obtained from shore connections. This eliminates the need for the vessels to run their generators all the time.
Steering
Steering is crucial for a ship’s manoeuvrability. Rudders are the primary devices used for steering. They operate on Bernoulli’s principle to create a pressure difference across the sides when the rudder is turned. This creates a horizontal lift (imagine a plane wing but placed vertically). The number and design of rudders depend on the vessel type. Compound or flapped rudders are a 2 piece construction wherein the main rudder panel has a flap at its trailing edge pivoted on its own axis. The flap can change the effective angle of attack to maximise the lift. Pump jet vessels use a nozzle to direct jet flow for turning. Rudders and nozzles are typically controlled using hydraulic systems, known for their reliability, accuracy, and power. These hydraulic pumps are powered by onboard generators. For smaller vessels and ferries, electric servo motors are used for steering.
Navigation
Manoeuvring ability is useless without a sense of direction. Especially when navigating the vast, open sea, the best of the sailors can lose track of path with the knowledge of position, heading and weather conditions. Since shipping nowadays is all about efficiency, a longer path to a destination is also detrimental to the profitability of the business as extra time and fuel is consumed unnecessarily. Modern day references and instruments make life much easier. Various navigational aids are employed to ensure safe and efficient voyages, with the most significant ones discussed below.
Gyro Compass/Magnetic Compass
A compass provides directional information between 0 to 360 degrees corresponding to the true north of the earth. Naturally, East falls at 90 degrees and west at 270 degrees respectively. A ship's heading can now be defined in terms of the angle relative to true north. For eg. a heading of 315 degrees signifies that the vessel is pointing North West. A gyroscope operated compass (gyro-compass) is standard on all vessels and is unaffected by the Earth’s changing magnetic fields, making it more accurate than a magnetic compass. The spinning gyroscope in a gyro compass aligns accurately with the Earth’s rotational axis, pointing to true north. Although a magnetic compass, which relies on the Earth’s magnetic field, may not always be accurate, it is still useful for route planning before a voyage.
RADAR
Radio Detection and Ranging (RADAR) utilises specific radio frequencies (X-band and S-band) to detect targets that reflect radio waves. The reflected signals are displayed as targets on a screen, allowing the determination of the distance of objects. There are several types of RADAR onboard a vessel, each having a specific purpose. Navigation, weather tracking are the common purposes while naval warships can have systems for air and surface targets, weapons guidance.
AIS
The Automatic Identification System (AIS) contains vital ship data such as speed, heading, destination, and cargo details, including hazardous materials. AIS operates on the VHF radio channel, enabling the identification of ships using this database. The AIS information can form some great datasets for automated route planning of autonomous vessels, collision avoidance and priority settings in a multi vessel traffic such as the South - China sea.
VDR
The Voyage Data Recorder (VDR) is akin to an airplane’s black box. It records bridge communication and messages, providing a 12-hour playback capability. The VDR is crucial for investigations in case of incidents.
Supply & Service
A tonne of auxiliary systems are fitted onboard with each serving a certain purpose. Remember the network of pipes I mentioned in the intro? That’s exactly what I shall explain to you now. Piping networks are used to carry fluids (liquids or gases) from their source to the destination compartment. Obviously a fluid would not move upwards or horizontally without applying an external force. That's where pumps come in. depending on the type of fluid, one or several pumps are employed to impart force to the fluid. Fluid force can be summarised as a product of flow rate and pressure. Tweaking the size of pipes and fittings such as valves, reducers and couplings can help engineers to play with these values. With the scientific principle out of the way, let us get down to understanding the types of systems present on a typical maritime vessel.
Fuel Oil Transfer
Propulsion and power generation make use of liquid fuel (marine diesel oil, gas oil or heavy fuel oil). This fuel is stored in tanks under the belly of the ship. There are multiple tanks for starage rather than a single tank to reduce loss due to damage and maintain stability. When fuel is consumed from one tank, that part of the ship becomes lighter. This imbalance is mitigated using a network of piping that redistributes fuel to maintain balance. A fuel transfer network facilitates this process, supplying fuel to the engine and power generators.
Lube Oil Transfer
Mechanical parts of the engine, generators, shafts rudder and variable pitch propellers require continuous lubrication. Lubrication not only reduces frictional resistance but also carries away contaminants and heat away from the working surfaces. A closed loop is operated from a lube oil pump sending oil to areas of use. The used up lube oil is collected in a dirty oil tank through a network of lube oil pipes. Centrifuges are used to separate impurities from the oil, which is then pumped back to the relevant systems. Both fuel and lube oil systems have shore connectors to refill tanks with fresh fluids.
Fresh Water System
At sea, only saltwater is available, but freshwater can be generated through a process called reverse osmosis (RO). Freshwater is required for drinking and domestic purposes like cooking and cleaning. Seawater is picked up from inlets at the bottom of the hull called ‘sea chests’. large scale RO purifiers are employed to produce potable water and stored within freshwater storage tanks. For a fact, the RO systems onboard mega cruise ships are able to produce enough freshwater for an entire city within a day.
HVAC System
Heating, ventilation, and air conditioning (HVAC) systems are essential for cooling ship compartments and maintaining moisture levels. Ships and large sailing vessels are meant to travel to different parts of the world and under different climates. But a stable climate control within the vessel ensures comfort for crew and passengers. For merchant vessels carrying refrigerated cargo, dedicated temperature and moisture level control becomes necessary. Machinery on the bridge also requires climate control. Marine HVAC plants generally have the capacity equivalent to 100 home AC systems. They are installed based on the quantity of air flow required and the conditions to be maintained. Dedicated refrigeration systems are installed for cargo that requires specific temperature control.
Ballast-Deballast System
To maintain stability and positive metacentric height during loading, unloading, and voyages a dynamical system that allows ship masters to adjust the attitude of the vessel is required. The ballast - deballast system is such a provision where ballast tanks are filled or emptied. This alters the buoyancy of the vessel. When water is pumped in using high flow rate ballast pumps, the vessels draft increases i.e it sinks further. When water is removed, the vessel's draft decreases (becomes more floaty). These tanks are typically located at the extreme bow and stern (the extreme front and ends) to provide effective draft and trim control.
Bilge and Oily Water Separators (OWS)
Bilge residue is formed as a result of processes, condensates of fuel, oil and water vapours. This residue flows at the lowest part of the ship where it is collected in bilge tanks. Positive displacement bilge pumps transfer bilge to oily water separators (OWS). The treated residue is released into the sea, while the remaining residue is cleaned at port calls. It is illegal to dispose of waste in the sea without proper treatment. The violation of MARPOL conventions by any vessel can cause heavy penalties. OWS ensures the level of pullotants is within the prescribed values.
High-Pressure Air System
High-pressure air is used for numerous applications onboard. Pneumatic workshop tools, galleys, sanitary systems, and pneumatically operated davits and lifts, OWS, pressure starting for engines are a few to list. Onboard air compressors pressurise air to about two hundred times the atmospheric pressure and store them in a network of bottles (large tanks) across the vessel. The air bottles supply pressurised air at their local low pressure air networks. The pressure is dropped for appropriate application use through converging nozzles.
IPMS
The Integrated Platform Management System (IPMS) is a special mention here and is a system in the control domain. It encompasses controls and interactive interfaces for all ship systems, allowing for remote operations from any part of the vessel. This eliminates the need for personnel to manually visit faraway and often inaccessible locations in the vessel to check for problems. The IPMS provides a virtual chart of all systems, ship status, pinpoint warnings, and overall remote control. Remote operation saves overall time for system diagnosis and operation.
Antifouling
Continuous contact with water leads to marine fouling on the ship hull, causing drag and reducing efficiency. Antifouling systems prevent the growth of such foreign material. With a wide range of working principles available for antifouling, the most common type is an antifouling coating which can be cleaned through scrubbing. The electrolytic method with sacrificial anodes is also popular and used in most modern vessels. A clean hull does a much better job of cutting through water, saving precious fuel and time.
Degaussing Coils
Residual magnetic fields develop from continuous operations of motors and other devices, potentially disturbing communication channels and navigational instruments. Degaussing is a procedure to neutralise the residual fields through coils with controlled current that eliminates excess magnetic fields. For naval vessels, managing magnetic signatures is crucial to avoid detection and triggering sensitive weapons.
Onboard Safety
Safety systems are paramount on all vessels, ensuring the well-being of the crew and passengers. The SOLAS Convention dictates mandatory safety regulations to all categories of marine vessels. These regulations are formed as a result of all accidents that ships have suffered in the past and hope to reduce their occurrence again. Let us take a look at some of the safety systems onboard a typical merchant or passenger vessel.
Firemains System
The firemains system is crucial to deal with fires onboard. The system draws water from sea chests, and pumps provide flow to a ring main loop. The system triggers on fire or smoke alerts, especially in the engine room, which is prone to fires due to high heat operations. Different types of fires require different firemain systems. The older CO system created a toxic environment for the crew to enter the 2 room post extinguishment. Moreover, it wasn’t completely safe to enter the room due to a high chance of re-ignition. This was eventually replaced by the water mist system which is highly reliable, uses less water and is suitable for compartments where flooding can cause more damage. Salvage System In the event of flooding on a ship due to water ingress or a damaged hull, there is a significant danger of the ship sinking. To mitigate this risk, a robust salvage system is employed. This system includes very high flow rate centrifugal pumps designed to expel water faster than it enters the vessel. These pumps are strategically located at the lowest points of the hull to ensure maximum efficiency in water removal. The water is then discharged out of ports located on the sides of the hull. This system is critical in maintaining buoyancy and stability, buying valuable time for the crew to address the damage and prevent the ship from sinking.
Life Boats and Life Rafts
Both lifeboats and life rafts are available on the ship for emergency evacuation. The primary difference between them is that lifeboats are equipped with engines and can be operated like a normal boat, while life rafts do not have engines and are intended for passive flotation. The total capacity of these lifesaving devices must be at least 125% of the onboard capacity, ensuring ample space for all passengers and crew in case of an emergency. This capacity is divided equally on both sides of the ship, allowing for balanced evacuation procedures and increasing the chances of a successful rescue operation.