Wind-assisted propulsion is a method used to help commercial ships use less fuel by adding sails or other tools that capture wind energy. In the past, sails were the main way to move ships, but after steam engines and diesel engines were invented, sails were mostly used for fun sailing. Recently, because fuel prices have gone up and there is more focus on reducing pollution, there is growing interest in using wind power to move large ships again.

A major challenge in using wind-assisted technology, especially for reducing carbon emissions, is the need for money. Shipping companies are borrowing less money overall, and building or upgrading ships to use low-carbon methods costs more than usual. Because of this, researchers are working on new ways to share the benefits of these technologies. These ideas include systems where savings from using less fuel, or gains from carbon credits and lower fees, are shared among people who use the technology, the companies that make it, and the ship operators.

Design

Scientists are studying how to use wind energy to help ships move. Early ships were built mainly to sail, with large sails that pushed them forward. Today, commercial ships are designed to carry large amounts of cargo, requiring open decks and less overhead equipment for easier loading and unloading. When designing wind-powered systems for these ships, engineers must ensure that the system does not need a large crew to operate and does not affect the ship's stability. Based on these requirements, four main wind-assisted propulsion designs have been developed: the wing sail, SolidSail systems, kite sails, and Flettner rotors.

In the 1980s, rising oil prices led the U.S. government to study whether wind-assisted systems could reduce fuel use in ships. This study found that a wingsail system would be most effective. Wingsails use large, rectangular sails attached to cylindrical masts. These sails are symmetrical, requiring little adjustment to work with different wind directions. However, this design was not as efficient as other options. A small freighter was tested with this system, and it saved between 15% and 25% of its fuel.

SolidSail is a wind propulsion technology for large ships, created by Chantiers de l'Atlantique in France. It uses rigid sails made of strong materials and a tilting rigging system, allowing ships to rely partly or fully on wind power. Three SolidSail units are currently used on the longest sailing ship ever built (as of 2026), the Orient Express Corinthian, which can sail entirely on wind power under ideal conditions.

The kite sail concept has gained attention recently. This system uses a large kite attached to a ship’s bow. The kite’s movement helps pull the ship forward. Some designs use a reel to move the kite up and down, powering a generator. These kites are similar to those used by kiteboarders but much larger. Multiple kites can be used together for greater power.

In 2012, kite sails were the most common wind-assisted system on commercial ships because they are inexpensive to install on existing ships and require little change to the ship’s structure. Computer systems control the kite’s position and angle for maximum efficiency. Kites can capture wind at higher altitudes, where wind is stronger and more steady. The MS Beluga Skysails, a merchant ship tested by the U.S. military in 2009, was one of the first ships to use this system.

The Flettner rotor is a large cylinder mounted on a ship’s deck that spins to create thrust. This idea was first developed in the 1920s and has been used rarely since. In 2010, a 10,000-dwt cargo ship was tested with four Flettner rotors to see if they improved fuel efficiency. Since then, several cargo ships and a passenger ferry have used this system.

The only part of the Flettner rotor that needs control is its spinning speed, which requires little human input. Compared to kite sails, Flettner rotors can be more efficient based on their size and wind conditions.

Examples of Flettner rotor installations in 2018 include:
• The cruise ferry Viking Grace became the first passenger ship with a rotor.
• The liquid bulk tanker Maersk Pelican was retrofitted with two rotors.
• The ultramax bulk carrier MV Afros received four rotors that can be moved during port operations.

Implementation

The improvements in efficiency from these three ship propulsion systems are usually about 15 to 20 percent, depending on the system's size. In 2009, shipping companies were not eager to use equipment that hadn't been tested yet. By 2019, many groups were studying whether using wind power would be practical and affordable for ships. These groups included the Swedish Oceanbird project, which uses special sails called wing sails, the Japanese Wind Challenger Project, and other organizations working together.