A second wind for maritime shipping?

Doom-scrolling YouTube can help you think about tech!

Well, sort of.

In football, the Magnus effect is what causes a spinning ball to curve mid-air - like when Roberto Carlos bends the ball around a defensive wall by creating pressure differences on either side of the ball.

In maritime shipping, Flettner rotors harness this same principle by spinning vertical cylinders on a ship’s deck, generating thrust perpendicular to the wind direction and reducing the vessel’s reliance on traditional fuel.

I had two chats with a VC and a maritime tech founder this week that had me thinking about wind-assist technologies.

I think it’s a space the UK and EU can be competitive and lead.

Maritime shipping is one of the world’s most carbon-intensive industries, responsible for around 3% of global CO₂ emissions. With new EU emissions regulations kicking in and the International Maritime Organization (IMO) targeting net zero by 2050, the sector is under pressure to slash its reliance on fossil fuels.

There’s also an associated financial saving from reducing fuel consumption.

But electrification is barely an option for large ocean-going vessels. It works in smaller sizes like Candela or the one I could find for <100 containers cargo - but not for mass logistics that helps the world tick. Batteries are too heavy, and alternative fuels like ammonia and green methanol remain expensive and logistically complex.

And so ship operators are literally looking for tail winds. Enter wind-assisted propulsion—a pretty low-tech, high-impact solution that’s making a serious comeback. Wind power is proving to be a viable and scalable way to cut fuel costs and emissions.

Wind-assisted propulsion isn’t about bringing back old-school sailing ships (sorry Dad).

Today’s wind-powered shipping tech comes in several formats, each engineered to complement existing propulsion systems. The first is rigid-wing sails - think of these as aircraft wings mounted vertically on ships, designed to optimize lift and maximize thrust from the wind. UK-based BAR Technologies has pioneered this approach with WindWings, massive 37.5m sails capable of reducing fuel consumption by up to ~30%. Partnering with Cargill, these sails have already been tested on the Pyxis Ocean. Similarly, Spain’s bound4blue offers eSAIL® technology, a system of vertical rigid sails that automatically adjust to wind conditions. They recently secured a deal with Maersk Tankers to retrofit their fleet. AYRO’s "Oceanwings" has developed automatable, reefable wing-sails designed for commercial vessels, aiming to enhance propulsion efficiency.

Another option is ‘flettner rotors’, spinning cylinders using the ‘Magnus effect’ (the same principle behind curved football shots) to generate forward thrust for the vessel. Finnish company Norsepower has installed rotors on ships for Maersk and Viking Line, reporting fuel savings of 5-20% depending on wind conditions. Anemoi Marine Technologies has developed a similar rotor sail systems with tilting mechanisms to facilitate cargo operations and port navigation. These approaches are capable of producing significant propulsion force, especially on crosswind courses, and generally occupy less deck space compared to fixed sails.

There’s also kite-assisted propulsion, which is exactly what it sounds like. French startup Airseas, a spinoff from Airbus, is developing Seawing, an automated parafoil kite that can tow massive cargo ships. It promises fuel savings of up to 20% with minimal structural modifications to vessels.

Each wind-assisted propulsion technology—rigid-wing sails, Flettner rotors, and kite-assisted propulsion—offers distinct advantages and trade-offs, largely shaped by their operational mechanics and integration challenges. Rigid-wing sails provide high aerodynamic efficiency and durability but demand significant deck space and careful handling in varying wind conditions. In contrast, Flettner rotors excel in generating high thrust through the Magnus effect while maintaining a compact footprint, yet they require motorized rotation, adding mechanical complexity and energy consumption. Kite-assisted propulsion, leveraging high-altitude winds, minimizes deck interference and offers potential fuel savings, but its reliance on automated deployment and retrieval systems introduces operational challenges.

From a venture perspective, I think rigid sails and rotors are gaining traction due to their predictable performance and easier integration into existing fleets, whereas kites—while promising—face hurdles in widespread adoption due to their dynamic nature and dependency on specific wind conditions. The ultimate viability of each approach hinges on vessel type, trade routes, and advancements in automation and materials science, with continued innovation shaping their role in decarbonizing maritime shipping.

All of these technologies have the advantage that they can be retrofitted onto existing vessels, making them more accessible than costly newbuilds designed around alternative fuels. There are more than 60,000 ships engaged in international trade daily - including container ships, bulk carriers, tankers, and general cargo. So refitting is key to decarbonize the sector.

The UK and EU already have the regulatory frameworks, maritime expertise, and funding mechanisms to support wind-powered shipping at scale.

The EU’s Emissions Trading Scheme (ETS) now requires shipping companies to pay for their carbon footprint, pushing operators to explore lower-emission technologies. Countries like the UK, Finland, and the Netherlands are home to some of the world’s most innovative wind-assisted propulsion startups. The UK’s Clean Maritime Demonstration Competition has poured millions into wind-assist R&D, while the EU’s Horizon Europe program continues to fund shipping decarbonization projects.

Despite its promise, wind-assisted propulsion still faces hurdles.

Installing wind systems can cost millions per vessel. Without clear financial incentives, many shipping companies hesitate to invest. Crew training and route optimization are also needed to maximize efficiency - the wind-assist only works if there is wind on the route (going in the right direction). Wind systems work best with smart weather routing, but adoption of AI-based planning tools is still growing. Large rigid sails and kites also require extra space and adjustments at ports, potentially complicating docking procedures. The industry is also historically risk-averse. Many operators prefer waiting for “proven” technologies, delaying mass adoption.

That said, there’s a huge market opportunity. The global shipping industry spends over $120 billion annually on fuel. Even a 10% fuel savings industry-wide would translate to $12 billion in cost reductions—not to mention the impact on emissions and the climate.

Startups that combine wind power with AI-driven fleet optimization, financing solutions, or modular retrofit designs could play a critical role in scaling adoption.

The golden age of the sail might be gone, but the maritime industry might be about to get a second wind.