What is a propulsion system?
Watercrafts, either big or small, that possess the capability to move on their own have a system fitted within them responsible for creating the necessary power to move. This system of the ship is called the propulsion system or more specifically, the marine propulsion system of the watercraft. In simple terms, the propulsion system generates thrust to push the vessel forward.
How does it work?
Marine propulsion works according to Newton's 3rd Law of Motion which states that “Every action has an equal, opposite and instantaneous reaction”. The propulsion system pushes water in the direction opposite direction of ship motion creating an equal and opposite force to propel the ship.
How has it changed over time?
Shipbuilding has been around for ages. According to Berg (2023), the oldest “seaworthy” vessels were developed around 6500 BC in the Northern Europe of today. Marine vessels back then were small in size, mostly propelled by human-powered oars. These crews rowed in a rhythmic pattern to create a combined forward thrust by pushing their oars through water. Another ingenious technique was the use of wind. Huge sheets of cloth were installed on tall masts onboard the vessel. These were called sails and were usually controlled by a complex set of ropes and pullies. Sails were used for many decades thereafter and proved to be a successful means of moving a ship across the ocean. With the Industrial Revolution, mankind discovered the reciprocating steam engine. A range of mid- size watercrafts like lake boats and ocean liners utilised paddle wheels along with these engines which were generally powered by coal or wood. Raw seawater was used to produce steam in the boilers as it was readily available. A very important innovation in this timeline is the screw propeller, which became the fundamental component of all propulsion systems since the early 1800s and is still in use today. Finally, in the past few decades, the rise of internal combustion technology like diesel engines and gas turbines and advanced forms of steam turbines changed the marine propulsion scenario. The advancement in propeller design has had a great impact in this field. There are a few newer innovations for marine propulsion. These systems are complicated in terms of design but highly effective. Read on to know more about them…
What are the main components?
Any modern marine propulsion system consists of three basic components: An energy source, a prime mover and a propulsion device. A vessel may have one or multiple types of these components. All three are vital to the functioning of the vessel. The choice of each component decides factors such as performance, efficiency and capabilities.
Energy Sources
The propulsion system will derive its power from some type of energy source. Over the years, a conscious effort has been made to create sustainable energy. A sea-going vessel also requires some form of energy to move forward. There are several such sources and each one has its own unique pros and cons.
Wind
Wind is by far the most abundant and historically popular energy source found at sea. It can range anywhere from a light breeze to gusty storms capable of destroying entire cities. The global maritime industry has been very clever in harnessing this energy to its use since the very beginning and is still finding new ways to do so with modern technology. Sailboats in the past used square sails that directly intercepted the wind in the direction in which it flowed. However, this meant that ships could only travel forward when the wind blew directly behind the vessel. This was a problem due to which a large variety of sail shapes were introduced which could generate motion even if the wind blew in different directions. Sails are still in use on recreational crafts and smaller, 1 or 2 man crewed sailboats that are operated close to the shoreline. These sails are now manufactured from a combination of different materials such as composite fibers, natural cotton and hemp cloth (Ocean Navigator, 2011). Weaving and molding patterns enable them to have the required strength and service life while being lightweight and easily controllable.
Advantages
The biggest advantage of wind sails is that they are completely emission-free. They only make use of the natural flow of wind to propel the ship. Moreover, they are the cheapest form of propulsion system. Sails also rank very high in terms of reliability at sea, as there are no moving parts and there is no requirement for secondary equipment to run the system, unlike engines that undergo wear and tear while also consuming fuel and lubrication agents. They are less likely to fail.
Disadvantages
The downsides of wind sails are majorly related to the performance aspects. Sailboats tend to be slow to move and are heavily dependent on wind speed and direction. Low wind speed and the vessel will find it hard to make progress. High wind speeds can make things haywire and out of control. Maneuverability is also an issue. Sails have to be adjusted all the time to match the wind conditions. Sailboats, for example, have to weave left and right adjusting their sails every time to effectively move in one particular direction. That is a lot of work for the crew. Hydrocarbon Fuel Hydrocarbons by far are the most reliable and easily available sources of energy for the entire world. In the shipping industry too, hydrocarbon fuels such as marine gasoil (MGO) and heavy diesel oil (HFO) are the standard fuels as ships run large-capacity diesel engines and gas turbines. A hydrocarbon is simply a compound formed from only 2 elements: Hydrogen (H ) and Carbon (C). 2 These two elements form long chains of 12-16 carbon atoms surrounded by hydrogen to pack loads of energy in chemical form. Burning such compounds releases energy as heat and it is capable of moving mechanisms like pistons and turbine blades. Heavy fuel oil and marine gas oil form a cheap solution to all the energy needs of a fairly large vessel. Apart from these, there are other fuels such as Liquefied Natural Gas (LNG), ammonia (NH ), 3 methanol (CH OH) and biofuels (Bushiri, 2022). These are a great replacement as alternate fuels 3 to conventional heavy fuels. Their use has been increasing since the past decade as they produce cleaner energy and reduce greenhouse gases. Advantages Hydrocarbons are the cheapest and the most established form of fuel available at the moment. They can be refined at a much cheaper cost and provide decent performance characteristics to modern vessels.
Disadvantages
Hydrocarbon produce toxic gases like carbon monoxide (CO), sulphur compounds and carbon soot. These toxins remain suspended in the air or settle on the sea surface. Especially in cities with busy ports, the problems of air pollution due to the arrival and departure of gas-guzzling merchant ships are significant. Governments around the world are concerned about this prominent issue. The introduction of non-polluting electric or alternative fuel vessels can be a promising solution. The use of tri-fuel engines (engines that can switch between conventional fuel or gas fuel like LNG) is being investigated to reduce the effects of maritime activity on the local population.
Nuclear Fuel
Nuclear technology has been one of the greatest sources of clean energy. Nuclear power plants on land generate enormous amounts of energy with a relatively small amount of fuel. The same technique but at a compact scale is made possible for sea-going vessels. A nuclear reactor works on the principle of nuclear fission where the nuclei of atoms are split. Heavy elements such as Uranium (U) are mostly used in land based power plants. For a marine reactor, a special form of alloy containing Zirconium (Zr) is used. The fission reaction releases energy in the form of heat and gamma radiation. The heat component is then used to generate steam in a boiler to drive the steam turbines.
Advantages
First of all, nuclear energy is clean energy. There are no emissions. Nuclear vessels can go without refueling for years without any drop in output. This is especially useful for naval operations where a vessel may have to stay running for longer mission roles (SOFFAR, 2016). Only human constraints such as food resources may require the ship to do port visits. The efficiency of nuclear reactors is much more than other conventional fuel sources. This means that nuclear powered ships can support equipment and crews of personnel onboard for a decent period of time. Nuclear vessels are also recyclable.
Disadvantages
Nuclear powered ships and submarines are extremely complex to operate and only a few trained personnel (especially naval forces of some countries) are able to handle such vessels. The cost of operating nuclear-powered ships is also very high.
Hydrogen FC or Fuel Cells
Hydrogen (H ) stands as a promising alternative for fueling the energy requirements of many modern 2 vessels as well as any future innovations in propulsion systems. Hydrogen is a very energy-dense fuel that when combined with oxygen releases energy to generate electricity. The only byproduct of this reaction is water which is obtained at the exhaust. At present, this technology is in a very primitive stage. Hydrogen is tricky to store as compared to hydrocarbon fuels. Many energy firms around the world are researching different ways to solve this issue. Even though it may not be as energy dense as fossil fuels, it still provides a viable means of energy production.
Advantages
The biggest advantage of hydrogen-based energy is that it is abundant and readily available (TWI, n.d.). Also, it is renewable and carbon neutral. It can be produced in a much more compact way as compared to other renewable energy sources. The only byproduct of its combustion is water and heat. Also, it ticks the safety measures, compared to other, more powerful yet hazardous sources of energy like nuclear. It is also energy efficient. In times when the world seems to be progressing towards renewable energy, hydrogen is exactly the type of fuel the maritime sector requires. With hydrogen energy and hydrogen-powered vessels, shipping companies can reduce their reliance on fossil fuels.
Disadvantages
The most challenging part of producing hydrogen energy is the extraction of hydrogen itself. Some processes like electrolysis of water are preferred methods. For hydrogen production, however, a lot of energy is also consumed to run these processes. In return, a very small quantity of useful hydrogen is produced. The process itself is also very expensive and requires expensive metal catalysts. At the moment, the price of hydrogen energy may be on the higher side. However, with mass production in the future, they are bound to fall. There also arise safety concerns with this type of fuel owing to the fact that hydrogen is extremely flammable and would thus require a robust infrastructure and storage facility.
Solar Energy
Solar panels are some of the most widely used renewable energy devices. A majority of land-based renewable energy sources are in fact solar energy based. Such an abundance of renewable energy sources can also be used at sea to power ships or offshore structures. Solar panels, used to create solar energy are basically silicon panels having different crystal configurations. The main types of these configurations include amorphous, polycrystalline and monocrystalline types (Bluetti, n.d.).
Advantages
A solar panel uses energy from the sun to create charges within its crystal structure. Sunlight is abundantly available everywhere and it is also free of cost. The only cost of this energy type is the instalment of solar panel devices. Solar panels have a versatile design and can also be fitted on curved surfaces which make them quite sturdy in extreme climatic conditions as well. They have the capacity to provide a decent amount of power output with a reasonable form factor.
Disadvantages
Solar panels get heavier and bulkier when higher specific power output is expected (from one solar panel). It continuously requires sunlight in order to produce energy a few other things like accumulators may also have to be purchased in order to store energy during the day and for use during the night time. In the maritime industry, solar panels are yet to be implemented on vessels. The issue with this is that current technology is not capable enough to produce enough power for a sea-going vessel along with its electrical propulsion system and other equipment.
Prime Movers
A prime mover is a device that converts any form of energy to useful mechanical energy. It is mostly imparted in the form of rotational energy which can be used to drive a shaft or can just be used to drive electric generators. There are some typical prime movers available for ships based on their working conditions.
Stirling Engines
Even though stirling cycles may be a thing of the past now, they have been a significant part of many maritime vessels. There may still be some vessels using the stirling engine for propulsion. A stirling engine is a type of a heat engine that uses air working fluid with its compression and expansion in order to create mechanical energy. In most cases stirling engines operate with a fixed amount of air within the chamber. This air can expand and compress to create a pressurised or partial vacuum environment so that the piston is either pushed or pull in the chamber. The air in the chamber can be expanded or contracted in volume by heating and cooling processes.
Advantages
Stirling engines are very well known to have very low noise levels while operating. This is because there is no combustion as such within the engine chamber. They are also highly reliable due to a smaller number of moving parts. These engines were constructed to be extremely simple in terms of their design and hence it was also very easy to repair them. The engine itself does not produce any polluting components however, the method of heating the gas chamber determines the overall level of its efficiency.
Disadvantages
The temperature limit to operate the stirling engines is quite high and hence, more amount of fuel would be required to achieve high temperatures. These engines must be carefully balanced and there can also be frictional losses between the piston and the cylinder wall.
Diesel Engines
Talk about workhorses of modern fleets, the diesel engines are now an industry standard. A diesel engine is categorised as a ‘Compression Ignition’ (CI) engine. Diesel oil is injected into the combustion chamber at very high pressures. The piston compressors the diesel air mixture to a point where the temperature inside the chamber reaches a value higher than the self-ignition temperature of diesel. This creates huge amounts of energy that pushes the piston down. A typical diesel engine for any vessel can generally have about 12 to 16 cylinders driving the crankshaft.
Advantages
Diesel engines are some of the most efficient devices available in current times. They do get hotter than the gasoline counterparts, however give a higher efficiency value overall. When it comes to fuel prices, ship operators are always looking for a setup which has the best fuel usage. Due to the high temperatures, they are made to bear the heat, hence in general they are very durable as well.
Disadvantages
Diesel engines like any other internal combustion unit has a lot of moving parts which can be troublesome during maintenance. They still have a lower power to weight ratio. Larger capacity ships can use multiple engine units to drive multiple propellors.
Gas Turbines
Gas turbines are internal combustion engines which burn fuel to expand air. This air is expelled out of the turbine nozzle at extremely high velocities. This creates thrust. The expanded air is used to drive a turbine shaft within the engine which drives the compressor to compress air at a very high pressure. In ship propulsion, gas turbines are not directly connected to the propellor shafts. A secondary turbine called the drive turbine is rotated by the thrust. Or in some cases, a Synchronous Shift Gearbox (SSS) can be used to couple the gas turbine.
Advantages
The power output of a gas turbine is probably the highest of all prime movers. The most specific term used to define power output is the ‘power to weight’ ratio. Gas turbines probably have the highest power to weight ratio when compared to other types of prime movers. It only consists of rotating parts such as the compressor and turbine along with the shaft which is much easier to balance than reciprocating devices. Gas turbines also occupy less space within the ship. Modern gas turbines also contain the option to run alternative fuels.
Disadvantages
As I mentioned, gas turbines can you produce tons of power but at the cost of high fuel consumption. Gas turbines themselves are very intricate in their construction and design and can sometimes make maintenance a hard job for the crew. They also operate at very high temperature and almost all of that heat is dissipated via the exhaust in the atmosphere. In order to withstand such high heat, the components are made from exotic engineering materials sometimes costing much more than an entire diesel engine. Gas turbines take time to start and reach their operating condition. So the ship crew has to plan the startup procedure in advance and keep the engine alive until it may not be required.
Electric Motors
Latest types of prime movers seen the shipbuilding industry are electric motors. With the advent of renewable energy sources, perhaps, electric motors just prove to be the best option for marine vessels. Again, electric motor technology has now significantly reduced the cost of operation of a decent motor which may be virtually maintenance free. The fundamental principle of an electric motor is that it converts electrical energy into mechanical energy as compared to big diesel engines and gas turbines which work on a source of chemical energy.
Advantages
Firstly, electric motors have a very small form factor. They require a minimum lubrication arrangement against friction but do not involve any major procedures such as oil changes. When it comes to performance, electric motors provide instantaneous power and torque which results in better thrust. The operation is mostly silent and there is no reason to deal with hot exhaust gases. Electric motors do not require any special treatment during cold weather which makes them ideal for use in any part of the world. Recent scientific research has also paved the way to regenerative electrical processes where the electric motor can also double up as a generator in the opposite direction to harness power that may be typically lost as heat.
Disadvantages
An electric motor still requires electricity which has to be either generated on board or with the help of accumulators supplied by the port of call or the shipping company. The exchange of batteries is still an expensive affair. Moreover, they are limited in range. A longer range means that the vessel would have to carry more batteries which would be extra weight. Besides, the initial cost of this method her very high however mass production can bring the cost down.
Propulsion Devices
Propulsion devices work on Newton's Third Law of Motion which basically says that any action will always be accompanied by a similar reaction on an object. In this context, if there is a way to exert force on the fluid, the fluid will in turn exert a reactive force on the vessel which pushes it forward. There have been many innovations for the different types of propulsion devices. Propellers have stood the test of time and are widely popular. But there are a few more substitutes.
Shafted Propellors
Shafted propellers are the most preferred choice of propulsion mechanisms and are still preferred today's times due to their comparatively reliable design and operation. A propeller looks like a fan having a certain number of blades attached to a central hub. These blades are angled in such a way that they push fluid behind them when rotated. This creates the reaction force pushing the vessel ahead. Some model propeller designs allow ship handlers to vary the blade angle and thus increase or decrease the thrust without having to change the direction of rotation. Such propellers are called ‘Controllable Pitch Propellers’ (CPP). The efficiency of a propeller is highly dependent on the profile of its blades and the conditions it has to operate in. The use of shrouded propellers is done in certain kinds of tugs to create a concentrated high thrust.
Advantages
Shafted propellers are run by the ship's engine through a long shaft protruding out of the hull. This is a fairly simple arrangement and is also used as a standard in almost every maritime vessel event today.
Disadvantages
The gap between the hull structure and the propeller shaft has to be sealed in order to prevent water ingress while also allowing the shaft to rotate freely. Propellers themselves cannot change the direction of a ship and hence must be used in conjunction with a rudder. The shaft and propeller assembly must be installed very carefully has a long shaft may undergo deflection during operation or due to self-weight. A propeller may also catch unwanted elements in the sea (fishing nets, seaweed) which may end up decreasing its efficiency or jamming it completely.
Waterjets or Pumpjets
Water Jet Propulsion or simply ‘waterjets’ are a high velocity alternative for propulsion mostly famous for high-speed crafts. The construction of this type of propulsion device is a little more complex but highly effective. This propulsion system literally sucks fluid from the bottom of the boat or craft and forces it out from the rear creating the action and reaction effect. It can be imagined more or less like the operation of an axial water pump.
Advantages
Water Jet Propulsion does have moving parts similar to the impeller of an axial pump however it is not exposed to the open environment. Hence the chances of damage due to collisions with an object are minimal. Since the output of this is a high velocity water jet, direction control can be achieved by directing this water jet with the use of nozzles and reverse can be obtained by employing a reversal bucket.
Disadvantages
The efficiency of a water jet system decreases quite rapidly as its size increases. Hence this type of propulsion system is best suited for small-sized crafts that operate at very high speed. Compared to a propeller it also consumes more amount of power.
Azipods
Taking propellers to the next level of control maneuvering are azipods or azimuthing thruster devices. The word ‘azimuth’ is used to express any angular measurement from a fixed reference point. This type of propulsion system also works in a 360-degree fashion and can virtually provide thrust to the vessel in any direction. Propellers in this system are connected to the engine through a complex mechanism having non-parallel shafts between them. The propeller and its shroud are mounted on a stock under the hull of the ship and are free to rotate in any direction. They virtually have no restrictions on the thrust direction and form a good option for vessels that require high maneuverability. Their use is not restricted to just small vessels. Some of the larger cruise and merchant vessels also make use of this technology.
Advantages
The biggest advantage is, of course, the maneuverability these thrusters offer. Moreover, they are also very efficient in their operation and can be driven by a variety of prime movers. It is also easier to carry out maintenance tasks on these as they form a swappable unit and can be dismantled within no time. A new unit can also be replaced if the existing one is beyond repair.
Disadvantages
Azipods are not cheap. A piece of technology capable of providing more control will definitely incur higher costs. They are also not the easiest to control and the personnel handling such ships have to undergo training to use them effectively.
Special Propulsion Systems
Air Independent Propulsion
This is a more recent development in terms of submarine propulsion. Conventional diesel electric submarines use an onboard diesel engine to produce electricity which runs the electric propulsion motors. However, such a submarine has to resurface to provide its engine with oxygen and a way to release its exhaust gases. This is usually done through a process called ‘snorkeling’. To sum it up, the diesel engine cannot be run when the submarine is underwater. Nuclear powered submarines, on the other hand do not need oxygen to produce energy. The waste products of the process are too harmful to be released into the ocean and are hence stored onboard to be cleared at port. Hence nuclear subs can stay underwater for much longer than conventional diesel electric subs. AIP provides these subs with an underwater running alternative. Boats with stirling or diesel engines require the production of heat to run, which can be provided by using fuel and compressed oxygen with certain inert gases like Argon. This is a form of AIP. Hence no atmospheric exposure is required. In recent times, fuel cells with hydrogen and oxygen are used to chemically react and generate electricity. This is also an AIP as the end product “Electricity” is produced underwater, which is the only requirement to run the propulsion motors.
Magneto-Hydrodynamic Propulsion
All propulsion systems discussed so far, except wind energy, have some moving parts involved. The magneto-hydrodynamic drive system purely works on the Lorentz force generated as a result of the interaction between a current-carrying conductor and a perpendicular magnetic field. Saltwater forms a good conductor of electricity. The arrangement of this system is made such that the sea water is ionised into its hydrogen and hydroxide components which are propelled by the induced force called Lorentz force. The body is propelled in the opposite direction. To better understand this phenomenon, we can consider the right-hand rule which states that if we stretch our right thumb, index and middle fingers such that they are perpendicular to each other and consider that the index and middle fingers show the magnetic field and current respectively, then the thumb will show the direction of Lorentz force. The water ions will also travel in this direction and thus a propulsive force will be generated. Now, the speed and direction control with such a system depends on the current value and flow direction and also the distance between the two electrodes. But the larger the size of the vessel, the greater the amount of current required to create any useful propulsion force. Also, it is not efficient as some part of the energy goes towards ion bubble formation. So, this technology has seen only a few working prototypes. The good part is that there is minimal wear and tear as friction is completely absent.
Hybrid Propulsion
A better option to combine the specific attributes of several types of propulsion systems is to utilise a combination of them. This is typically termed ‘hybrid’ propulsion as either one or more systems can be used to propel the vessel. These are mostly employed by vessels that demand specific performance characteristics at particular events, like naval vessels. Modern naval vessels use a combination of gas turbines in conjunction with diesel engines as their powerhouse. More recently, electric propulsion has also been implemented with propulsion motors and turbines or diesel-electric generators. These systems also follow the ‘AND’ or ‘OR’ that all propulsion methods have to be used together to run the vessel whereas, ‘OR’ generally means that there is a choice of propulsion onboard and each can be used independently or together depending on the situation.
Gas of Trifuel Propulsion
Shipping vessels usually use Marine Diesel Oil (MDO) or Heavy Fuel Oil (HFO) as fuel for their propulsion plants. However, the possibility of using Liquefied Natural Gas (LNG) is also being investigated by companies like Wartsila and MAN. A tri-fuel engine, as the name suggests, is capable of running on either one of these fuels. The main idea here is to reduce the emissions caused by ships when near the territorial waters of a country. Pollution caused by the use of MDO or HFO can easily cause harm to the local environment. Natural gas though, is a cleaner source of energy and can be used to operate ships near the shore. MDO and HFO can be used as normal when under a voyage on high seas.
Skysails
Wind energy has again gained relevance through the concept of ‘Skysails’ which proposes the use of a kite-like apparatus to tow vessels around. It is very similar to kite surfing, where the surfers use kites to tow themselves. Applying such a concept to a huge vessel though has its own challenges. The most important of them is to prevent the kites from taking the vessels haywire due to unforeseen wind conditions. The ‘kite’ must also reach a height with reasonably strong winds, typically about 100-200m from sea level, and the related mechanisms to operate such a system must be made rugged.
Cyclorotors
By far the most complicated in terms of working, cyclorotors form a very unique and effective type of propulsion system. In principle, these are a set of equidistant blades protruding out of a circular plate rotating about its axis and mounted vertically below the keel. The blades themselves can rotate about their axis. The pitch angle of each blade is constantly adjusted on every rotation, so that they always provide positive thrust in a particular direction and zero thrust otherwise. This system is much more efficient and faster in response than the conventional azimuth thrusters. When it comes to cyclorotor technology, the most famous design for marine propulsion is the Voith-Schneider Propellor which is used by tugboats and vessels requiring high maneuverability. They are expensive too and hence are used only where absolutely needed.
Flettner rotors
The concept of Flettner Rotors is not recent. It has been tried on many vessels previously. To picturise this in a better way, Flettner Rotors look like tall poles mounted on deck more like the electricity poles you might see on a road. They are made in such a way that their circumference can rotate are variable RPMs. This caused the Magnus Effect due to wind flow across the rotating surface. Imagine that the wind blows at right angles to the ship from port (LHS of ship) to starboard (RHS of ship) as the rotors rotate in the clockwise direction when viewed from the top. The wind moving across the back will face resistance due to opposite wind and rotor directions and the wind velocity at the back will decrease. But the opposite will happen in the front of the rotor as both wind and rotor move in the same direction. This creates higher pressure at the back and lower pressure at the front of the rotor, eventually exerting a forward-pushing force on the vessel.
How to determine which propulsion systems to use?
Although selecting the right ship propulsion plant is a very complicated process, involving several factors, I’ve still tried to jot down a few of the classifications that can be considered to choose the most appropriate option. In many ways, all factors are related to each other and it is up to the client and shipbuilder to decide an option.
Based on Ship Role and characteristics
The ship's role can be anything from cargo transport to passenger or naval operations. Cargo ships would require a strong and powerful plant to set a gigantic cargo mass into motion and be efficient at the same time. Passenger crafts are all about comfort and would be best fitted with a silent and low emissions propulsion system. It would also require one with smooth operation characteristics. Naval vessels are more towards multirole operating capabilities and require a fast-moving system.
Based on Fuel Economy
Fuel economy is of utmost importance for any maritime vessel operator. Hence the decision merely lies on the specific requirements. The newer Integrated Electric Propulsion (IEP) systems are way more efficient in power conversion and are equipped with smart monitoring systems onboard, that can suggest fuel-saving sail patterns for a planned voyage. But again, several factors play a part in this process and a thorough consideration of all options is required.
Based on performance
If outright speed is considered, gas turbines are the most suitable options as seen mounted on a majority on naval vessels around the world. But this reduces the fuel economy. For smaller watercrafts, the use of waterjet propulsion can also be considered. For more maneuverability, cyclorotors or azimuth thrusters with controllable pitch propellors can be used.
Based on Ship Size
This factor may not be specifically only related to the type but also the power output of the system. Bigger vessels will require a much bigger diesel steam engine to operate are a decent pace. Smaller vessels can utilise smaller units or even some other systems like waterjet propulsion.
What is the future of propulsion systems?
The general trend shows that electric propulsion will gain more traction in the future, simply because of its efficiency, quietness and lower emission characteristics. The transition will be slow though. A lot of ships may be “retrofitted” with newer propulsion systems. However, the best performance can be extracted from vessels built keel up to be electric vessels. Apart from this, safer nuclear power or perhaps, even the old school wind energy can be used again, considering the use of renewable energy in the maritime sector.
FAQ:
How are marine engines protected from sea environment?
There are many precautions one can take. The main motive is to prevent salty air to react with the vessel parts. For the hull, protective layers of anti-rust material, or the sacrificial anode method can be employed. The seals and gaskets for piping systems have to be checked regularly. It is also recommended to use freshwater for cooling systems. Are marine diesel engines 2-stroke (2S) or 4-stroke (4S)? They can be either. It just really depends on the application. 2S engines tend to run at higher RPMs and also are less fuel efficient. They are also lighter and smaller in size. 4 strokes on the other hand are quite opposite to 2 stroke counterparts.
References
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