Clippers were boats created in the early 1800s intended for fast ocean transport: the entire ship was designed to achieve maximum speed and saw maximum use from roughly 1830 to 1870 when they were supplanted by steam-powered transport ships.
To increase speed, these boats had a sail surface larger than that of their equivalent ships, which made them difficult to maneuver (in fact, they had specialized crews). One of the most famous and fastest was the Cutty Sark.
For a few years, following the resolution by the International Maritime Organization (IMO) which set the objective of halving emissions from maritime transport by 2050 [see box], we have started talking about wind-powered cargo ships again. Let’s see a fewexamples of contemporary projects.
WIND ENERGY
The industry has pledged to reduce planet-warming pollution to zero “by or around 2050”: using wind is one way to achieve this. While this is not a new concept (sailing ships date back more than 5,000 years), new wind propulsion technology has appeared in recent years.
The technologies that exploit the wind are basically huge kites and rotors. Both have been trialled on merchant ships in an attempt to reduce their dependence on diesel. We are still at the experimental level with regards to kites; while, according to the International Windship Association, there are around 20 large commercial ships equipped with wind propulsion technology (rotors) at sea. There is still a long way to go, because these are expensive technologies and, when it comes to industry acceptance, cost is key, and the price of oil has a big influence. But interest grows along with oil prices and the push for sustainable shipping.
CARGO KITES
What are sailing cargo kites? The principle is that of kitesurfers, which exploit the power of the wind to surf on the sea; however, in the case of merchant ships the surface of the kite needs to be around 1,000 sq.m. This is the idea of Seawing, developed by the French company Airseas, which could help merchant ships reduce fuel consumption and carbon emissions by an average of 20%.
The founders are two aeronautical engineers who have been working on this technology since 2016; for more than a year, a 250-sq.m version of the Seawing has been tested on the 154 m long ‘Ville de Bordeaux’ chartered by Airbus (which owns a minority stake in Airseas), sailing across the Atlantic.
The wing is not only pulled by the wind but, as it flies, it turns forming 8 ins which multiply the effect of attraction of the air flow, increasing the power of a very compact and simple system placed on the bow which can be adapted to any vessel.
Vincent Bernatets, co-founder and CEO of Airseas, commented: “We validated Seawing’s automated dynamic flight to start decarbonization maritime using the power of the wind. Based on the latest trials, we are now able to project initial results of 16% fuel and emissions reductions, in line with our broader development roadmap. The performance will be optimized with upcoming onshore trials. After 7 years, seeing our kite flying in ‘figures of 8’ over the Atlantic Ocean in complete autonomy, to deliver first tonnes of traction, is a huge satisfaction, and a demonstration of how our aerospace expertise allowed us to pass major technological challenges”.
The tests continue with the aim of achieving large-scale industrialisation; the company has received 2.5 million euros in EU funding and says it already has orders from Airbus and Japanese shipping company “K” Line. They hope that the technology will be fully operational by the end of 2025.
STEEL WINGS
The WindWings are made of steel and GFRP, stand 123 feet tall, and use the force of the wind to create lift and move the ship forward; they can be folded on deck when entering port or passing under a bridge to avoid collisions.
They were fitted to the Pyxis Ocean in Shanghai (owned by Mitsubishi Corporation and chartered by the US shipping company Cargill), before the vessel travelled to Singapore where she was refuelled and officially launched. The performance of the wings will be carefully monitored along the way, so improvements can be made to the design before it is produced at scale.
Pyxis Ocean is equipped with two large steel sails 37.5 m high, designed by the British company BAR Technologies and produced by the industrialization partner Yara Marine Technologies which program already plan to create hundreds of them in the coming years.
The wings are expected to generate emissions savings of up to 30%. When used in combination with alternative fuels, the savings would be even greater, enhancing the transition to green shipping solutions.
WIND-POWERED MERCHANT SHIP
Oceanbird is a concept for wind-powered cargo ships, born in 2010, developed to eliminate emissions from shipping, called the ZERO emission project. The concept aims to reduce emissions by up to 90%, and the design was developed in collaboration with the KTH Royal Institute of Technology and the Swedish maritime technology company SSPA.
Just like an airplane uses air pressure to move upwards, the Oceanbird wing sail uses it to move forward. The air flow on the other side of the wing goes faster than the air beneath, and the pressure differential generates so called lift.
Wallenius Marine, with its design and logistics expertise, was the project coordinator. KTH has addressed challenges in areas such as aerodynamics, sail mechanics and performance analysis. SSPA has contributed to the development and validation of new test methods, aerodynamic and hydrodynamic simulation methods, and risk simulation. SSPA is also performing extensive model tests: a 5-m long model has now been tested in SSPA’s large basin, the Maritime Dynamics Laboratory in Gothenburg, Sweden.
In 2022 the new Oceanbird wing sail consists of a core and a flap, optimizing the aerodynamics forces. It is half the size (40-m high, 14-m wide) but shows the same performance as previous design, allowing a smaller footprint: both environmental and on deck.
Testing of the prototype took place in 2023 and will continue into 2024. Meanwhile, Oceanbird is investigating solutions for placing wing sails on existing vessels in different maritime segments. The first ship with all-wind propulsion will set sail in 2027. Last August, the first wing sail from Oceanbird, Wing 560, has received Approval in Principle (AiP) from the world’s leading classification society DNV.
AUTOMATED INFLATABLE SAILS
The well-known tire manufacturer Michelin has designed WISAMO (WIng SAil MObility), giant inflatable sails made from a flexible material that the company declined to reveal. They look more like the ‘Michelin Man’ than a traditional cloth sail, they can be fitted to existing cargo ships and inflate or deflate at the push of a button – making it easy for the ship to enter a harbour or pass under a bridge.
No crew is required to rig them, and they automatically rotate to catch the wind, equipped with sensors that measure wind direction and speed. The sail has now obtained Approval in Principle (AiP) from the classification society DNV: this is the first AiP to have been assigned to an inflatable wing sail design and is currently being installed for testing on the DNV classified MN Pélican.
WISAMO was first introduced in 2021, is automated with a system developed by Michelin R&D and can be installed on commercial and recreational vessels.
Are sailing boats coming back?
Advanced wind propulsion technology systems that can be retrofitted to existing vessels have the potential to provide substantial energy and fuel saving benefits, but are they really the future of the shipping industry? Many doubts and uncertainties are slowing down their adoption.
Above all, the economic feasibility of the technology, since there are no guarantees of cost-effectiveness and also of safety; however, the wings help reduce the ship’s emissions and also help owners comply with new industry standards on energy efficiency and save money by reducing fuel consumption.
Certainly, decarbonization maritime demands substantial investment across multiple areas, and the global sustainable shipping industry must proceed in the transition towards greener and cleaner propulsion and design. Surely, clippers will not come back, the new sails do not resemble those of the ancient ships: but green shipping solutions surely have a future in the decarbonization of the planet.
In 2023, the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO), the agency responsible for developing global standards for shipping and supporting countries in implementing them, adopted the revision of the objectives of the Strategy on greenhouse gas emissions of the sector, which include: a 20% reduction in emissions by 2030; a 70% reduction by 2040 (compared to 2008 levels); the ultimate goal of achieving net zero emissions by 2050. The new regulations are expected to come into force around mid-2027.
The greenhouse gas strategy includes: decreasing the carbon intensity of the ship through further improving energy efficiency by strengthening the requirements for new ships; reduction of CO2 emissions from international maritime transport by at least 40% by 2030, compared to 2008; adoption of technologies, fuels and/or energy sources with greenhouse gas emissions equal to or close to zero to represent at least 5%, aiming for 10% of the energy used by international maritime transport by 2030. The shipping industry produces more than one billion tons of carbon dioxide each year, accounting for nearly 3% of human-caused global emissions.
