How wind propulsion is making cargo ships more efficient

When hundreds of sailing boats compete against one another during Kiel Week - the world's largest sailing event - their driving force is the wind. Yet the event's significance extends far beyond the world of sailing. Right here in Kiel, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is conducting research into how wind can also make cargo ships more climate-compatible in the future.

Modern wind-powered propulsion systems have little in common with the sailing ships of past centuries. Rotors, wing sails and automated sailing systems are based on aerodynamic insights from aviation and are increasingly seen as a key component in the decarbonisation of shipping. DLR is taking this a step further, focussing not just on the sail itself, but on the entire ship as an energy system - from the hull design through to batteries and hydrogen storage, weather-dependent route planning and on-board energy generation.

The DLR Institute of Maritime Technologies and Propulsion Systems, with its facilities in Kiel and Geesthacht, is investigating how wind energy can be used as efficiently as possible for freight transport. Annika Fitz, an engineer specialising in energy systems for ships, and Lars Schmitz, a naval architect and expert in wind propulsion, both work at DLR and explain the topic in this interview.

Are we seeing an increase in the use of wind propulsion in commercial shipping?

Lars Schmitz: Yes, we are currently observing a clear upward trend. According to the International Windship Association (IWSA), more than 100 large ships are now powered by wind propulsion. In the last six months alone, there has been an increase of over 25 percent. The pressure to decarbonise is growing, and at the same time, more and more shipping companies are recognising the benefits of wind propulsion. Wind is a renewable energy source that is available directly where it is needed, making it particularly interesting for the shipping industry.

Why is this technology making a comeback now?

Schmitz: The conditions have changed. International shipping must significantly reduce its emissions, while alternative fuels such as methanol, hydrogen, or ammonia will remain expensive and in limited supply for the foreseeable future. Every kilowatt-hour of energy directly harnessed from wind reduces the demand for these energy carriers. At the same time, wind propulsion makes shipping and the economy less dependent on global energy markets and more resilient to energy price shocks. This makes it not only ecologically and economically attractive but also strategically advantageous.

Many people think of sails first when they hear "wind propulsion". However, DLR often refers to the 'whole-ship system'. What does that mean?

Annika Fitz: We view the ship as a complete system. This includes the hull, sails, propulsion system, energy storage, alternative fuels and operational strategy. Only when these components are optimised together can significant savings be achieved, and the energy from the sails that is not used for propulsion can also be used effectively.

Why should a ship in strong winds not only sail, but also generate energy?

Fitz: That very question was at the heart of our Hyro project, which we carried out in collaboration with industry and academia. The idea was to use sails as the main propulsion system for seagoing vessels. In favourable wind conditions, they can generate more thrust than is required for the desired speed.

Schmitz: This energy potential can be harnessed through energy recovery. The Hyro project investigated how excess energy generated by the movement of the ship's propeller can be converted into electricity via hydrogenerators. This electricity can be used directly on board or stored in the form of hydrogen. In this way, the wind not only helps the ship to move forward but can also supplement its energy supply.

What projects is DLR currently pursuing in this field?

Fitz: Odyssa is currently one of our key cross-institute projects. It is a software framework that enables us to analyse and evaluate different ship designs. It draws on experience gained from earlier projects such as Hyro. At the same time, we are continuously expanding Odyssa to include, for example, stability analyses, safety aspects, manoeuvrability and the evaluation of new energy systems.

Schmitz: In addition, we are working with industry collaborators and research institutions to improve performance forecasts for wind propulsion systems and are investigating new concepts for weather routing and ship optimisation.

Which sail systems currently have the greatest market potential?

Schmitz: That depends very much on the intended use. Rotating cylinders, as well as suction and wingsails, are suitable for both retrofitting existing vessels and newbuilds. When it comes to retrofitting, we are working to make larger wingsails possible - for example, through additional hydrodynamic elements such as directional stabilising fins or adapted rudders. For newbuilds, large-scale systems such as the DynaRig are of interest, in which the masts and sails turn according to the wind direction, under computer control.

Is retrofitting existing cargo ships the quickest way to reduce emissions?

Schmitz: In the short term, yes. The existing fleet will remain in service for many years to come. That is why retrofitting can make an important contribution. In the long term, however, the greatest potential will lie in ships that are designed for wind propulsion from the outset, with all components working together optimally.

Which ships are particularly well suited to wind propulsion, and which are less so?

Schmitz: Ships undertaking long ocean voyages with favourable wind conditions are of particular interest. However, suitability always depends on the specific operational profile. These are precisely the kinds of questions we investigate using our simulation tools. Not every ship benefits to the same extent, which is why a thorough assessment is important.

Where are wind propulsion systems already being used today?

Schmitz: There are already several commercial applications. The cargo ship 'Canopée', which transports Ariane 6 launch vehicles from Europe to Europe's Spaceport in French Guiana, uses modern wingsails. From 2026, Airbus also plans to deploy a new fleet of transport vessels equipped with Flettner rotors. These are intended to transport aircraft components between European production sites and assembly plants in the United States. The number of such projects is growing steadily.

How large are the actual fuel savings in day-to-day operations?

Fitz: The absolute savings depend heavily on factors such as weather conditions, route, ship design and the desired operating speed. For existing vessels that are retrofitted with wind-assisted propulsion systems, fuel savings of between 5 and 30 percent are common. Our research shows that the potential becomes significantly greater when wind propulsion, the energy system and the operational strategy are optimised together.

Schmitz: Very substantial savings can be achieved with specially developed ship designs. The key factor is always to consider the vessel as an integrated system. Many of the ships with higher sail power have only recently entered service. Reliable measurement and quantification of the resulting savings therefore remains a research topic in its own right.

Can wind-powered propulsion systems alone meet the shipping industry's climate targets?

Fitz: Probably not. Wind propulsion is more likely to become an important component of a future maritime energy system rather than a standalone solution.

Schmitz: The shipping industry will most likely rely on a combination of technologies, including wind energy, batteries, hydrogen and synthetic fuels. Wind can play a significant role in reducing overall energy demand.

Why is DLR particularly well-placed to carry out this research?

Fitz: We are able to bring together expertise from a range of disciplines. As far back as the 1920s, wind tunnel tests at the Aerodynamics Research Institute (Aerodynamische Versuchsanstalt; AVA) in Göttingen - a direct predecessor organisation of DLR - contributed to the development of Flettner rotors. The aerodynamics of modern sails also benefit from insights gained from aviation, and in addition we possess extensive expertise in energy systems, batteries and hydrogen technologies.

Schmitz: Added to this is our expertise in marine engineering and test facilities for fuel cells and propulsion systems, including those in the newly established laboratories in Kiel and, in the future, aboard our MODULARIS floating laboratory. This allows us to examine the entire system, rather than individual components in isolation.

Let's look to the future: What will merchant shipping look like in 2040?

Schmitz: I expect there to be significantly more wind-assisted ships than there are today. Wind propulsion will become increasingly commonplace - not as a return to the past, but as a modern technology.

Fitz: The shipping industry of the future will intelligently combine various energy sources. Wind will play an important role in this because it is readily available and helps to reduce the demand for climate-compatible fuels. That is precisely why it is worth consistently tapping into this potential today.

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DLR showcases its research at Kiel Week

During Kiel Week, visitors will have the opportunity to learn about DLR's latest research on maritime energy systems, alternative propulsion technologies and climate-compatible shipping. The exhibition will take place on 25 and 26 June 2026 as part of the 'Science Comes to Town' programme at the Schlaumachwiese on the Kiellinie waterfront in Kiel. Visitors will be able to see models of a refuelling station and the MODULARIS floating laboratory, as well as take part in an interactive hydrogen experiment.