Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or engine turning a propeller, or less frequently, in pump-jets, an impeller.
Choice of a suitable powerplant depends on: size of the ship, speed (type of cargo), length, duration of voyage, cost (operational expenses) and fuel. Earlier marine propulsion used steam turbines however, due to advancement in technology, diesel or alternative fuel engine and gas turbine have greater penetration. Ships are integrated with one or more than one propulsion engines, depending on their size (gross tonnage).
Diesel propulsion system is the most common marine propulsion system used in all types of vessel along with small and recreational boats. Moreover, diesel marine propulsion engine led the overall market, accounting for 70% in 2015. This is attributed to its benefits such as high reliability, economical nature, low maintenance cost, and easy availability of diesel globally. The cons are they are more expensive to build , generate more noise and vibration and are heavier.
By the mid-1900s, the Navy had harnessed nuclear power for submarines and aircraft carries. The nuclear powered submarines have large endurance or mission times before resupply, limited only by the available food and air purification supplies on board. This eliminated the need for submarines to surface to recharge batteries, significantly improved stealth and performance, and improved the range and speed of aircraft carriers. Surface ships equipped with nuclear propulsion have long refueling intervals and do not need to be accompanied by vulnerable fuel supply tankers. Nuclear reactors producing steam are also used to propel warships and icebreakers. Nuclear reactors to power commercial vessels has not been adopted by the marine industry.
This century finds the Navy moving to electric hybrid gas turbine propulsion plants, again improving efficiency and reducing the need to refuel, while increasing operational availability and performance. The German Navy’s fourth and final new F125 frigate Rheinland-Pfalz uses a reliable and powerful GE LM2500 gas turbine-based propulsion system. These gas turbines reliably operate the world over in some of the most arduous conditions in temperatures ranging from -40 to 120 degrees F/-40 to 48 degrees C. All four of the new F125 frigates built for the German Navy employ one GE LM2500 gas turbine, two electric motors and four diesel generator-sets in a combined diesel-electric and gas turbine (CODLAG) propulsion arrangement.
New generations of ship must meet new challenges, particularly in terms of energy efficiency, reliability and environmental impacts. One of the future goals of shipbuilding is to reduce the impact of ship emissions to respond to existent and future regulations of the International Maritime Organization (IMO) on greenhouse gas and pollutants emissions.
Big ships, large engines also mean large amount of pollution. Ships produce above 2 per cent of CO2 emissions every year. This is expected to increase to 17 per cent by 2050 as sea travel is and will continue to be the main mode of economic transport.
The global availability and development of infrastructure makes LNG as bunker oil feasible. Development in liquefied natural gas (LNG) fueled engines are gaining recognition for their low emissions and cost advantages. While LNG is an excellent technology for reducing SOx and NOx emissions, it only reduces CO2 by about 20 per cent over bunker fuel. Stirling engines, which are more efficient, quieter, smoother running producing less harmful emissions than diesel engines, propel a number of small submarines. The Stirling engine has yet to be upscaled for larger surface ships. Analysts predict that the number of LNG-fueled ships will be more than 200 by 2020.
Wind propulsion emerged as an alternative to those systems which emit huge quantities of CO2 gases in the marine atmosphere. However, the usage of wind turbine marine propulsion has not started extensively in large commercial ships because of a requirement of constant windiness. Two wind propulsion systems for ships that have become lately are- kite propulsion and sail propulsion for merchant ships.
Until recently, American, British, and Russian nuclear submarines have used steam produced by the onboard nuclear power plant for propulsion; the steam would drive a turbo-gear unit, rotating the propeller. At the same time, French and Chinese nuclear submarines have used the principle of electric propulsion. The nuclear power plant set in motion turbines which are not connected to propellers, and which pump all their power into electric generators. The current from these generators, in turn, sets propulsion systems in motion.” Military analyst Vasily Kashin noted, the latter setup means decreased noise, but at the cost of a drop in maximum speed. Furthermore, “a great deal also depends on the quality of the installation itself, and other factors.
Electric motors using electric battery storage have been used for propulsion on submarines and electric boats and have been proposed for energy-efficient propulsion. An all electric ship propulsion concept was adopted for the future USA surface combatant power source. This next evolution or Advanced Electric Power Systems (AEPS) involves the conversion of virtually all shipboard systems to electric power; even the most demanding systems, such as propulsion and catapults aboard aircraft carrier.
Rolls-Royce Unveils Autonomous Naval Vessel Featuring Electric Propulsion
(Rolls-Royce) has announced plans for an autonomous, single role, naval vessel that will feature electric propulsion.
“Rolls-Royce is seeing interest from major navies in autonomous, rather than remote controlled, ships. Such ships offer a way to deliver increased operational capability, reduce the risk to crew and cut both operating and build costs,” said Benjamin Thorp, Rolls-Royce, General Manager Naval Electrics, Automation and Control.
“Over the next 10 years or so, Rolls-Royce expects to see the introduction of medium sized unmanned platforms, particularly in leading navies, as the concept of mixed manned and unmanned fleets develops. With our experience and capabilities we expect to lead the field.”
The initial design features a full electric propulsion system and features two Rolls-Royce MTU 4000 Series gensets to provide approximately 4MW electrical power to a 1.5MW propulsion drive. “An alternative to diesel engines could be small gas turbines, further improving the system’s reliability and reducing onboard maintenance,” explained Rolls-Royce.
“To reduce fuel consumption and extend operational range an additional 3000 kWh of energy storage will facilitate efficient low speed loiter operations and the vessel will also be fitted with photovoltaic solar panels to generate power when the vessel is on standby.”
The company notes that, with an absence of crew, autonomous vessels increases the need for reliable power and propulsion systems. In response, Rolls-Royce says the vessel will utilise a suite of autonomous support tools, including Energy Management, Equipment Health Monitoring, and predictive and remote maintenance to ensure vessel availability.
China’s new submarine engine is poised to revolutionize underwater warfare
In a recent interview with China Central Television, Rear Admiral Ma Weiming, a leading Chinese naval engineer, showed a component of a new Integrated Electrical Propulsion System (IEPS) for naval warships in a laboratory. He said the system, which turns all the engine’s output into electricity, and a rim-driven pump-jet had been fitted to the People’s Liberation Army Navy’s newest nuclear submarines. IEPS turns all the output of the ship’s engine into electricity, unlike traditional propulsion designs, which convert engine and reactor output into mechanical action to turn the propeller shaft.
The high electrical output can be used to power motors for the propellers or potentially high-energy weapons. Additionally, IEPS has far fewer moving parts, making them quieter, and thus ideal for use on submarines. When coupled with quieter reactors like the Type 095’s reported natural circulation reactor, the rim-driven pumpjet and IEPS can drastically reduce the acoustic signature of any SSN.
PLAN is fitting its newest nuclear attack submarines with a “shaftless” rim-driven pumpjet, a revolutionary and silent propulsion system, stated Chinese naval engineer, Rear Admiral Ma Weimin in the interview. The system is likely to be used on the first Type 095 nuclear attack submarine (SSN), which is under construction.The Type 095 SSN will likely have VLS cells for launching a wide range of cruise missiles, pumpjet propulsion, and improved quieting technology.
US and UK are also developing rim drive pumpjets, whose Columbia and Dreadnought nuclear ballistic missile submarine (SSBN) have the option for rim-drive pumpjets, but will not enter service until 2030.
Rim-Driven Thruster is a novel type of propulsion unit that has a ring-shaped electrical motor inside the pumpjet shroud, which turns the vane rotor (a vane rotor has the fan blades attached to a rotating band built on a cylinder interior, as opposed to a propeller shaft) inside the pumpjet cavity to create thrust.
The blades of the rim-driven thruster are mounted on a ring which constitutes the rotor of an electric motor. It is surrounded by the stator which is also ring-shaped and creates the necessary torque. Rotor and stator are water tight and the whole unit operates submerged.
The largest advantage of this building principle is its minimal noise emissions and the low space requirement. It enables relatively simple integration in many applications. Since the rotor is driven directly by the electro-magnetic forces, no shaft and no gearbox is needed. Sealing of moving parts is not necessary, rotor and stator can be sealed hermetically. Since the blades are mounted to the rotor ring, there is no tip gap. This, together with the gearbox removes prominent sources of noise. Rim-driven thrusters are therefore characterized by an extremely low level of noise emissions.
Previous submarine pumpjets are “shrouded propellers,” which consist of a tubular nozzle covering the propeller. By removing the shaft of the propeller, the reduction in the number of moving parts decreases the noise made by the pumpjet, as well as saving hull space. Civilian manufacturers also claim that rim driven pumpjets are easier to maintain, and have less cavitation (bubbles that form during propeller movement), making them even more quiet.
While the system would be on China’s attack submarine, Chinese SSBNs could also use the rim-drive pumpjet to enhance their stealth and survivability—and, by extension, the credibility of China’s second strike nuclear capability.
Ultimately, the commentator noted that “if China really achieves a sharp increase in the stealthiness of its nuclear subs, it will close the main gap in its military potential – the weakness of its submarine and anti-submarine forces. If Chinese nuclear subs reach silent operation indicators comparable to Western and Russian subs, it will make sense to rapidly increase the size of its submarine fleet. The fact that such a build-up is being prepared is evidenced by the expansion of the Bohai Shipyard [in Huludao, northeast China] in recent years. According to various sources, it is now possible to build 5-6 nuclear subs at the shipyard simultaneously.”
Finally, Kashin explained that the latter development will allow for a rapid growth of the naval component of China’s strategic nuclear forces, and alterations in the ratio of nuclear weapons deployed on the ground versus at sea. “It can be assumed that the construction of the prospective large nuclear-powered Type 096 submarines has been timed with the completion of development and testing of the IEPS system, and will now develop at considerable speed.”
Wind Propulsion: Commercial tankers using sail power to navigate the seas could be the wave of the future.
Norsepower Oy Ltd, a Finnish engineering and technology company announced in March the installation and testing of Flettner rotor sails onboard a Maersk Tankers vessel. The project, which will be the first installation of wind-powered energy technology on a product tanker vessel, would provide insights into fuel savings and operational experience.
Maersk Tankers will supply a 109,647 ton Long Range 2 product tanker, which will be retrofitted with two 98 feet tall by 16 feet in diameter Norsepower Rotor Sails. The design would look like narrow smoke stacks. Combined, these are expected to reduce average fuel consumption on typical global shipping routes by 7-10 percent.
The Norsepower Rotor Sail is a modernized version of the Flettner rotor — a spinning cylinder using the Magnus effect to harness wind power to propel a ship. Each Rotor Sail is made using the latest intelligent lightweight composite sandwich materials. When wind conditions are favorable, the main engines can be throttled back, providing a net fuel cost and emission savings, while not impacting scheduling.
Tuomas Riski, CEO of Norsepower, said in a release: “As an abundant and free renewable energy, wind power has a role to play in supporting the shipping industry to reduce its fuel consumption and meet impending carbon reduction targets.”
Global marine propulsion engine market is expected to reach $12 billion by 2022, growing at a CAGR of 4.1% from 2016 to 2022, according to report by Allied Market Research. The marine propulsion engine market is expected to witness robust growth during the forecast period owing to various ongoing government investments in shipbuilding industry and inland waterways.
The market segmentation is based on power source, ship types, and geography. The power source segment is divided into diesel, gas turbine, natural gas, and others (steam turbine, renewable energy, hybrid, and fuel cell). By ship types, the market is categorized into cargo & container, tanker, bulk carrier, offshore vessel, passenger ship, and others (tugs & service ships). Geographically, the market is spread across North America, Europe, Asia-Pacific, and LAMEA.
Increase in production & sales of ships globally and rise in international seaborne trade drive the market growth. In addition, increase in demand for resources such as crude oil, coal, steel, and iron from developing countries fuels the market growth. However, stringent environmental rules & regulations and large capital investment required to set up new manufacturing facilities hamper the market growth. Irrespective of these challenges, rise in usage of inland waterways and advancement in technology, such as new alternative fuel propulsion engine, are expected to provide various opportunities for new products and boost the market growth.
AsiaPacific is the most lucrative marine propulsion engine market, owing to increase in shipbuilding industries in China & South Korea and growth in number of joint ventures with international brands. Moreover, rise in seaborne trade of crude oil mostly from Middle East countries to AsiaPacific is another factor that drives the AsiaPacific marine propulsion engine market.
Types of Propulsion systems
Marine steam turbine was developed by Sir Charles Algernon Parsons. It provides Low noise, low weight, low maintenance costs, more space obtained (power /weight ratio raised) but have higher fuel consumption.
Most new-build ships with steam turbines are specialist vessels such as nuclear-powered vessels, and certain merchant vessels (LNG, coal carriers) where cargo can be used as bunker fuel.
Despite the universal move to GTs, diesel engines are still the primary power source for the majority of the world’s warships. There are many reasons for this: Diesels are durable, require less bunker space and are economical to operate as long as they are not continuously throttled up and down. They can draw on civilian infrastructure both for support personnel and for logistics provisions.
In Gas turbines, compressor draws in and compresses atmospheric air which is mixed with fuel injected in a combustion system and burned providing power from turbine to the shaft.
The gas turbine (GT) is rapidly becoming the standard surface combatant power plant used by navies across the world. The advantages of GTs for warship use include the capability for rapid acceleration and deceleration which is necessary in case of the ship coming under attack. In addition they have low noise, reliability, and power density. The design of GTs also facilitates the design of unmanned engine rooms, with consequent crew savings.
Gas turbines are commonly used in combination with other types of engine. Most recently, RMS Queen Mary 2 has had gas turbines installed in addition to diesel engines. Because of their poor thermal efficiency at low power (cruising) output, it is common for ships using them to have diesel engines for cruising, with gas turbines reserved for when higher speeds are needed.
Naval vessels incorporate the usage of nuclear maritime propulsion. Using the nuclear fission process, nuclear propulsion is a highly complex system consisting of water reactors and other equipments to fuel the vessel. The nuclear reactors in the ships are also used to generate electricity for the ship. Several merchant ships are also being planned to be constructed with this propulsion system.
Naval reactors use high burn-up fuels such as uranium-zirconium, uranium-aluminum and metal ceramic fuels in contrast to land based reactors which use uranium di oxide UO2. These two factors provide the naval vessels, theoretically infinite range and mission time. For these two considerations, it is recognized that a nuclear reactor is the ideal engine for naval propulsion.
Fuel Cell Propulsion
Fuel cell propulsion systems use hydrogen as the main fuel component. Electricity is created in the fuel cell without any combustion whatsoever. The process is clean and therefore has been regarded as a very important alternative marine propulsion system. There are various types of propulsion under the fuel cell propulsion head like PEM (Photon-Exchange-Membrane) and the molten-carbonate systems.
Biodiesel Fuel Propulsion
Biodiesel propulsion has been deemed as a potential marine propulsion system for the future. Currently tests are being carried out to find out about the viability of this propulsion system which is expected to be in full operation by the year 2017.
Solar propulsion for ships was utilised for the first time in the year 2008. Solar propulsion benefits include a high reduction in the poisonous carbon dioxide emissions. Solar propulsions are capable of generating a capacitance as high as 40 kilowatts (kW)
Water-jet propulsion has been used since the year 1954. The most important advantage of water-jet propulsion is that it does not cause noise pollution and offers a high speed to the vessels. In contrast the water-jet propulsion as a ship propulsion system is costlier to maintain which can cause problems to the user.
Over the last five years, a series of technical advances have turned electric propulsion from a technical backwater into perhaps the predominant form of warship powertrain for the next decade. The modern revival of this system was led by the British, who adopted a combined dieselelectric/ gas turbine (CODLAG) drive system for their Type 23 frigates.
The electric propulsion system consists of a prime mover which may be of two types: Diesel driven or Turbine or steam driven both generate mechanical energy and drive generators. The propeller shaft of the ship is connected to large motors, which can be D.C or A.C driven and are known as propulsion motors. Power for propulsion motor is supplied by the ship’s generator and prime mover assembly. Both the systems produce less pollution as compared to conventional marine propulsion system, which involves burning of heavy oil.
Instead of driving the ship’s propellers directly, diesel engines turn electric generators, which in turn power electric motors that drive the propellers. This arrangement enables diesels to be placed away from the shafts and propellers in sound-insulated compartments. Because the engines are not directly coupled to the shafts, their vibration does not pass along the shaft and thus does not get transmitted to the water as sound. An advantage of the system is that it eliminates the need for gears between the engines and the shaft. By doing so, removes a production bottleneck. The result is an almost silent propulsion system.