Wind-assisted propulsion: a guide for shipowners.
How cargo ships are using the wind again, what each technology does, what it can save, which ships suit it and how the rules now reward it. Written for owners, operators and technical superintendents.
What is wind-assisted propulsion?
Wind-assisted propulsion uses sails, wings, rotors or kites to let the wind push a motor ship forward, so the main engine needs less power for the same speed. The industry calls these systems WAPS: wind-assisted propulsion systems.
The engine stays. Whenever the wind blows from a useful angle, it takes a share of the work and the ship burns less fuel on that leg. In a calm the share is zero and the ship runs on its engine as it always has, so schedules and speeds are not left to the weather.
Most systems work like an aircraft wing stood on end. Air flowing past the sail creates lift at right angles to the apparent wind, the wind felt on deck once the ship's own motion is added to the true wind. The part of that force pointing ahead drives the ship.
Wind was the only way to move cargo across oceans for thousands of years. Modern wind propulsion is different: it is automated, it is sized to the ship's deck and routes, and it works alongside the engine rather than replacing it.
- Large ships with wind propulsion or wind-ready
- 100+
- Their combined capacity
- 6m+ DWT
International Windship Association, May 2026. Nearly three times the fleet of two years earlier.
The five types of wind-assisted propulsion.
Each turns wind into thrust in a different way, and each suits different ships.
| Technology | How it works | Strengths | Trade-offs |
|---|---|---|---|
| Rigid wing sail | Solid aerofoils, often with trailing flaps, generate lift like an aircraft wing and rotate to the wind | High thrust per unit; no power needed to spin or draw air; automatic trim | Needs deck length; must lower or feather for air draft, port calls and heavy weather |
| Rotor sail (Flettner rotor) | A tall spinning cylinder uses the Magnus effect to create lift | Compact footprint; well understood | Uses electrical power to spin; heavy foundations |
| Suction sail | Fans draw air through a thick, slotted wing to boost lift | Compact and modular | Uses power for the fans; smaller output per unit |
| Kite | A large kite flown high ahead of the bow tows the ship | Little deck space; reaches stronger winds aloft | Complex launch and recovery; works best downwind |
| Soft sail | Fabric sails set on masts, often automated | Simple and proven | Lower output per mast; more handling |
How much fuel can wind propulsion save?
There is no single number. Four things decide it.
The route
Wind strength and direction along the trading routes matter most. Long open-ocean legs with steady cross winds give the most; short coastal legs and head winds give the least.
The speed
The slower the ship, the larger the share of its propulsion power the wind can supply. Reviewing the Windship rig, the Wolfson Unit at the University of Southampton found a projection of about 30% annual savings for a rigged bulker or tanker reasonable at speeds below 12 knots, with optimal routing.
The sail area
More rigs, more thrust. For an 80,000 DWT Panamax bulk carrier at 12 knots, four Windship rigs are modelled at up to 49% fuel saving. That is a modelled figure for a reference vessel, not a sea-trial result.
How it is measured
The fairest measure is the share of propulsion power the wind supplies over a year. It is also the measure FuelEU Maritime uses to set its wind reward factor.
Which ships suit wind propulsion?
Slow, long-haul ships with open decks gain the most. That describes most of the world's bulk carriers and tankers.
Moderate service speeds
Bulk carriers and tankers, typically 10 to 14 knots, let the wind supply a large share of the power needed.
Long ocean passages
More days at sea in open water means more hours of useful wind each year.
Clear deck space
Rigs stand on the centreline between hatch covers, or on open tank decks, clear of cargo gear.
Deck strength and weight
Every system needs a foundation designed for the ship and approved by class. Heavier systems generally need more structural work and cost more cargo intake. Lighter systems widen the list of ships that can carry them. The Windship rig weighs about 150 tonnes.
Air draft and port calls
Bridges, loaders and cranes set how tall a rig can stand in port. Systems that lower, tilt or retract keep the trading pattern open.
How the rules reward wind.
Fuel you don't burn is now worth more than the fuel itself. Every tonne of heavy fuel oil not burned is about 3.1 tonnes of CO₂ not emitted, and not paid for.
FuelEU Maritime
Applies to ships of 5,000 GT and above on voyages to, from and between EU and EEA ports. It limits the greenhouse gas intensity of the energy used on board: 2% below the reference value from 2025, 6% from 2030, 14.5% from 2035, rising to 80% by 2050.
Ships with wind-assisted propulsion apply a reward factor between 0.99 and 0.95, set by the share of propulsion power the wind supplies. It lowers the ship's calculated GHG intensity by up to 5%, on top of the fuel it saves.
EU ETS
Covers cargo and passenger ships of 5,000 GT and above: all emissions on voyages between EU and EEA ports and at berth, and half the emissions on voyages into or out of the EU. Allowances cover 40% of 2024 emissions, 70% of 2025 emissions and 100% from 2026 emissions onwards.
UK ETS
Domestic maritime emissions for ships of 5,000 GT and above come into the UK scheme from 1 July 2026.
IMO Carbon Intensity Indicator
Ships of 5,000 GT and above receive an annual rating from A to E. Burning less fuel for the same transport work improves the rating, which charterers increasingly check.
IMO Net-Zero Framework
A proposed global fuel standard and greenhouse gas pricing mechanism for international shipping. Adoption was adjourned in October 2025, with talks resuming in late 2026.
Retrofit checklist.
Most of the ships that could use the wind are already at sea. These are the questions to answer for each one.
Route and speed profile
A year of voyage data, speeds and weather shows how much wind the ship actually sees and what share of power a rig could supply.
Deck layout and structure
Where each rig can stand, the loads it puts into the deck, and whether any reinforcement is needed.
Air draft and cargo operations
Bridges, loaders and cranes on the ship's regular ports, and how the rig lowers or stows for them.
Class approval
An Approval in Principle confirms the design is feasible. Type Approval certifies the production design, and plan approval covers the installation on your vessel.
Installation
Yard time, foundations, power and control connections, and crew familiarisation.
Measuring the result
Recording fuel burned and wind contribution so savings can be verified and claimed under FuelEU Maritime and in charterer reporting.
Questions shipowners ask.
What does WAPS stand for?
Wind-assisted propulsion systems. It covers rigid wing sails, rotor sails, suction sails, kites and soft sails fitted to motor ships to reduce the power the engine has to supply.
How much fuel does wind-assisted propulsion save?
It depends on the route, the ship's speed and how much sail area it carries. Published figures vary widely for that reason. For an 80,000 DWT Panamax at 12 knots, four Windship rigs are modelled at up to 49%. Model your own vessel to see its wind share.
What is the difference between a rotor sail and a wing sail?
A rotor sail is a spinning cylinder that uses the Magnus effect and needs electrical power to turn. A wing sail is a fixed aerofoil that rotates to face the wind and generates lift like an aircraft wing, without power to spin or draw air.
Can wind propulsion be fitted to an existing ship?
Yes. Most systems are designed for retrofit. The key checks are deck space, deck strength, air draft for the ship's regular ports, and class approval. Lighter rigs make retrofit possible on more ships.
Does wind propulsion count under FuelEU Maritime?
Yes, twice. The fuel saved lowers the energy the ship uses, and a wind reward factor between 0.99 and 0.95 lowers its calculated greenhouse gas intensity by up to 5%, depending on the share of propulsion power the wind supplies.
Do modern cargo ships still use sails?
Yes. More than 100 large ships now carry wind propulsion or are built wind-ready, with a combined capacity above 6 million DWT, according to the International Windship Association (May 2026).
Which ships benefit most from wind propulsion?
Ships that sail long ocean passages at moderate speeds with open decks: bulk carriers and tankers above all. The slower the ship and the steadier the wind on its routes, the larger the share the wind can supply.
Is the Windship rig approved?
The Windship triple-wing rig received DNV Approval in Principle on 6 September 2021. Type Approval will be completed with the first launch partner. The rig has not yet sailed on a commercial vessel. See the evidence.
Sources.
- Regulation (EU) 2023/1805 (FuelEU Maritime), European Union.
- FAQ: maritime transport in the EU Emissions Trading System, European Commission.
- IMO net-zero shipping talks to resume in 2026, International Maritime Organization.
- More than 100 ships now equipped or prepared for wind propulsion: IWSA, Ship & Bunker, May 2026.
- Windship performance figures: modelled for an 80,000 DWT Panamax bulk carrier at 12 knots. Wolfson Unit conclusions: Evidence.
See what the wind is worth on your ship.
Enter one vessel. See its wind share, fuel and carbon saved, and when the rigs pay for themselves.