The race to reach a decarbonized, “net zero” maritime industry by 2050 is, in some ways, similar to the advent of containerships some 70-plus years ago.
In the 1960s and 1970s, freight carriers, terminal operators, shoreside labor, engineers, and other interested parties tried out different container sizes, construction materials, and configurations before the familiar 40-foot and 20-foot steel container became standard and ubiquitous.
In a similar vein, more recently, a growing number of entities including ocean carriers, energy providers and developers, and even aerospace engineers are pooling their expertise to create a diverse selection of net zero marine fuel and propulsion systems with a variety of competing candidates vying to create and cultivate an industry standard or, at the very least, a competitive alternative.
No one is quite sure how the industry will shake out as the question looms as to whether one propulsion system will dominate or multiple solutions can co-exist. While a single dominating system would most likely be more efficient for terminal operators/refueling stations to adopt, a multi-option with competing technologies might well be more popular among ocean carriers because it would provide the flexibility inherent in having more operational choices.
What follows is a look at some of the more competitive marine propulsion technologies:
Ammonia
Ammonia is cheap and when used as a fuel emits no carbon dioxide. However, most ammonia produced today is created via a carbon-heavy process. Research is being done on so-called “green ammonia” that is produced from renewably sourced hydrogen in an electrolytic process, according to Norway’s maritime classification organization and marine advisor, DNV.
A research project at the Fukushima Renewable Energy Institute in Japan currently uses solar power and water electrolysis to produce small amounts of “green ammonia.”
Several marine engine manufacturers are currently working on ammonia prototypes either as a primary fuel or for use in ammonia-powered fuel cells that can be adapted to enhance existing power systems. Most experts think that ammonia will initially be best suited to propel tankers that already maintain specially trained crews. Several ocean carriers including Japan’s MOL, have expressed an interest in fueling new builds with ammonia.
The development of the infrastructure needed to handle ammonia fuel is also underway with several companies including ECONNECT Energy, unveiling new technology concepts. The Norway-based company recently unveiled its floating IQuay™ to safely transfer ammonia in bulk and for bunkering purposes.
The system enables connection to any terminal and ship type according to specific needs, and, the company says, “can be deployed quickly, cost effectively, and without the environmental impact of building conventional marine infrastructure.”
Nuclear
Nuclear power has long been used for military vessels such as submarines and ice breakers. Today, there is renewed interest in applying it to commercial vessel use with several variations in nuclear propulsion systems being considered to power a new generation of merchant ships.
Molten Salt Reactor (MSR): This technology uses the weakly radioactive element thorium rather than uranium, making it much safer than traditional uranium-powered reactors. The technology can either be used on board to directly power a ship, or as a power source for a floating refueling station providing electricity to battery-powered vessels.
One of the major research centers looking into MSR for vessels is the Norwegian University of Science and Technology, which has partnered with Knutsen OAS, a leading LNG tanker operator, to explore the MSR nuclear alternative.
Liquid Lead Cooled Reactor: This technology uses “liquid” lead as a coolant for a fast nuclear reactor instead of water. It has been used successfully in military vessels and in limited commercial uses. Like the MSR technology, it can be deployed either onboard or to power fueling stations.
A number of projects have sprung up around liquid lead, employing different configurations and designs. A British company, Newcleo, has designed a lead-cooled fast reactor specifically designed for naval and commercial shipping use that recycles nuclear waste products such as depleted uranium.
The large American tug-and-barge operator, Crowley Maritime, has announced a project to adapt nuclear power for onboard power plants and refueling, but a company press release did not specify the exact type of nuclear technology under consideration. Crowley’s plan envisions pairing traditional vessel propulsion with a mini-modular reactor capable of producing between five and 50 megawatts, which can be activated or deactivated as needed.
Gas-cooled Reactor (GCR): A gas-cooled fast reactor (GCR) replaces water as a coolant with a gas such as carbon dioxide or helium as a coolant instead of water. One advantage of GCR reactors is that they are lighter than comparable liquid lead designs. Although there are many other types of reactor cooled by gas, the term GCR is mostly used to refer to this type.
Sodium-Cooled Fast Reactor (SFR): This technology employs liquid sodium – salt – as a coolant for a fast reactor. Sodium is cheap, plentiful and lightweight. An early-generation SFR was used to power Seawolf, a U. S. Navy nuclear submarine launched in 1957. The technology is currently in use in several countries including the U.S., Russia, China, and India, while France and Japan are studying its various applications.
Belleview, Wa.-based TerraPower, is building a fourth-generation SFR called Natrium at a Wyoming power center and plans to build a similar reactor in West Virginia. Natrium’s design includes a storage capacity for molten salt that is heated by the reactor, which can then be tapped to produce energy. Terra Power is also working in concert with the British company Core Power to adapt SFR technology to create nuclear-charged fuel cell batteries for vessel powering use.
Methanol
Methanol is a simple alcohol that is currently made by capturing carbon from fossil fuels, usually natural gas.
As a fuel, methanol produces greatly reduced greenhouse gas emissions when compared to conventional diesel fuel and burns at a higher flashpoint. It is relatively simple to retrofit existing propulsion systems with dual-fuel methanol/diesel engines, making it a more attractive prospect than a fuel like ammonia which requires a much more complicated infrastructure re-design. However, conventional methanol cannot be considered fully “green,” since it is produced by utilizing fossil fuels.
Biomethanol: Biomethanol or “green methanol” is produced from biofuels such as methane from plant waste or cow manure.
The Canadian company Waterfront Shipping, a joint venture of Japanese carrier MOL and the giant methanol producer Methanex, has a small fleet of conventional methanol-powered ships under sail. This year, the company successfully tested bio-methanol to help power its tanker the Cajun Sun on a trans-Atlantic voyage, producing a net-zero transit.
In September, Danish shipping giant Maersk celebrated the arrival in Copenhagen of Laura Maersk – the world’s first container ship fueled with bio-methanol.
The 564-foot, 2,100 TEU feeder vessel is equipped with a main engine, developed by MAN Energy Solutions in partnership with Hyundai Heavy Industries, and an auxiliary Hyundai Heavy Industries Hi-touch Marine & Stationary engine capable of running on either methanol or diesel.
The company is planning to “green” its entire fleet by 2050 and is also developing the refueling infrastructure needed to support the new vessels.
Maersk has ordered six mid-sized container vessels – all with dual-fuel engines able to operate on biomethanol. China’s Yangzijiang Shipbuilding Group has been contracted to build the six 9,000 TEU vessels which will be delivered in 2026 and 2027.
E-Methanol: So called “electrofuel” or “e-methanol” is made by converting renewable electricity and biogenic carbon dioxide from biomass power plants into liquid fuel.
The Swedish start up, Liquid Wind AB, is a leading developer of e-methanol that has had several such facilities built in concert with multiple high-powered partners including Siemens Energy. A standard e-fuel facility, the company said, could produce up to 100,000 tons of green “electrofuel” and upcycle 150,000 tons of carbon dioxide per year.
LNG
According to the analyst DNV, the use of liquified natural gas in a maritime context “is now considered a mature alternative fuel option.”
However, it said, “one of the biggest challenges for LNG fueled vessels is finding the most efficient use of a vessel’s available space for the fuel tank and the associated systems. LNG storage on board requires more space than conventional fuel oil storage.”
This is primarily because LNG “has a lower energy density than fuel oil and therefore requires a larger tank to provide the same operational range. In addition, due to the low temperature of LNG, the tank insulation and required gas handling systems additional space is needed.”
However, “LNG engine design has been steadily improving as the technology becomes more widely adopted, with increases in efficiency and reductions in methane slip emissions.”
Isla Bella, the world’s first LNG-powered containership, was built by General Dynamics NASSCO in San Diego and was delivered to TOTE Maritime in October 2015. Its sister ship, Perla Del Caribe, was delivered to TOTE in January 2016.
Wind
Hard Sails: Hard sails are advanced, giant sails made of fiberglass or other materials that can be folded mechanically when not in use. They are controlled by sophisticated software that helps them pivot and move to harness the wind at the most optimum level for propulsion. Hard sails are already in use aboard pleasure craft and are being tested for smaller commercial vessels like barges and shuttles.
In August, the 80,000-ton bulk carrier Pyxis Ocean, completed a maiden voyage from Shanghai to Singapore after the installation of two massive steel and composite-glass Wind Wings.
The ship, chartered by commodity giant Cargill Inc., is the first vessel retrofitted with the hard sail system that can cut the vessel’s fuel use by roughly a fifth, the company said.
Sea Kites: Sea kites are very large, technically-advanced kites that harness the wind to help propel vessels, guided and controlled by computer software. Sea kites are not meant to fully propel a vessel but to act as a complement to an existing system.
The advantage with both hard sails and sea kites is that they can be deployed relatively easily and quickly and do not require a new engine or other significant types of retrofitting.
Japan’s “K” Line, is working with the French company Airseas to implement its Seawing automated, wind-assisted kite propulsion system aboard its smaller ships. First installed in late 2021 aboard Louis Dreyfus Armateurs’s 5,200 deadweight ton ro-ro cargo vessel Ville de Bordeaux, the system completed more than a year of tests before the wing successfully generated traction in May.
Rotor Sails: Rotor sails are large, vertical, rotating cylinders that are positioned on deck and resemble tall smokestacks.
They capture the power of the wind using an aerodynamic principle known as the Magnus Effect.
The cylinders are mounted vertically and when the wind blows from the side, the Magnus Effect creates forward thrust.
The effect is also used in a special type of ship stabilizer consisting of a rotating cylinder mounted beneath the waterline and emerging laterally.
By controlling the direction and speed of rotation, strong lift or downforce can be generated.
The concept of utilizing the Magnus Effect as the source of auxiliary marine propulsion is nearly a century old.
In 1925, the German engineer Anton Flettner oversaw the conversion of Buckau, a 467-ton schooner, which he refitted with two cylinders, or rotors, 50 feet high and 10 feet in diameter, driven by a 37kW electric propulsion system.
In June, the 82,000 deadweight ton Lady TR, a Cargill-chartered bulker fitted with three rotor sails manufactured by Anemoi Marine Technologies Ltd., completed a successful voyage between China and Australia.
Hydrogen and Hydrogen Fuel Cells
Hydrogen can be liquified and burned directly in a combustion engine, or it can be used to make fuel cells to power propulsion systems.
A small Compagnie Maritime Belge river shuttle ship currently operating in Europe called the Hydroville uses hydrogen directly as fuel, and CMB is developing infrastructure to support more vessels fueled in this manner.
A renewable energy source like solar can be utilized to power the electrolysis process that produces hydrogen – a process that experts feel could offset the disadvantage of it taking a “non-green” energy source to create the hydrogen fuel and hydrogen fuel cells in the first place.
This is an interesting conundrum as the original energy source needs to be “green” in order to meet global decarbonization goals.
The storage space required for hydrogen fuel is also an issue.
The diesel fuel needed to fill a ship’s bunkers is far less than the space needed to store the liquified hydrogen needed to achieve the same cruising range.
Electric
In 2020, Yara Birkeland, a small feeder containership operated by the Norwegian fertilizer company Yara, entered cabotage service in Norway.
The vessel is powered by conventional lithium-ion batteries, similar to the type of battery used in electric cars and is the largest all-electric vessel of its kind in use. The Yara can go about 30 miles between charges.
However, while conventional lithium-ion batteries can be used for smaller ships like the Yara which operate on relatively short routes, they are currently not large enough or strong enough to power large, ocean-going vessels with high cargo capacities.
A lithium metal battery, under development by Washington State-based Lavle, reportedly promises a much higher-powered, longer-lasting, and safer battery.
The world’s largest battery-driven ship is currently under construction in Australia.
The vessel, a 400-foot ferry, is slated for delivery in 2025. The uniquely designed vessel will be the largest ever of its type and also be the world’s first zero-emission, lightweight catamaran.
The ferry will reportedly be fully battery powered, with an eight-e-motor waterjet propulsion configuration and 40 mW battery modules and an energy storage system package said to be four times larger than on any electric/hybrid ship currently operating. •