Wind-Assisted Propulsion Systems (WAPS): A Game Changer for Maritime Decarbonization

The maritime industry faces increasing pressure to cut greenhouse gas (GHG) emissions and comply with strict environmental regulations.

Wind-Assisted Propulsion Systems (WAPS) offer a powerful solution by harnessing wind energy to reduce fuel consumption and emissions. This article explores what WAPS are, their types, benefits, regulatory aspects, and their role in decarbonizing shipping.

What Are Wind-Assisted Propulsion Systems (WAPS)?

WAPS uses wind energy to supplement a ship’s propulsion, reducing the need for traditional fossil fuels. These systems include rotor sails, suction sails, wing sails, soft sails, and kites.

Modern technology allows WAPS to integrate seamlessly with existing and newbuild ships, making them a viable option for reducing carbon footprints and operational costs.

Why Is WAPS Adoption Growing?

• Regulatory pressure from IMO, EU ETS, and FuelEU Maritime
• Rising fuel costs and carbon pricing
• Technological advancements making wind propulsion more efficient
• Increased focus on sustainability in global shipping

Types of WAPS: How They Work & Their Advantages

WAPS technologies differ in design, efficiency, and operational impact. Here’s a breakdown:

Type	How It Works	Benefits	Challenges
Rotor Sails	Cylindrical structures that rotate to generate lift via the Magnus Effect.	High efficiency, low maintenance, proven in commercial shipping.	Requires electrical power to spin.
Wing Sails	Rigid, airfoil-shaped structures similar to airplane wings.	High aerodynamic efficiency, good for various wind angles.	Complex operation, often requires tilting for ports.
Suction Sails	Uses air suction to enhance lift and reduce drag.	Efficient lift generation, good for stability.	Requires electrical power for suction.
Soft Sails	Reduces deck clutter, and operates above ship obstructions.	Lightweight, simple design, low cost.	Requires frequent adjustments and space on deck.
Kites	Complex operation often requires tilting for ports.	Large, tethered sails flying at high altitudes.	Limited effectiveness in crosswinds or upwind sailing.

WAPS and Decarbonization: A Path to Cleaner Maritime Transport

The shipping industry is under increasing pressure to decarbonize, with regulations tightening and fuel costs rising.

Wind-Assisted Propulsion Systems (WAPS) are emerging as a powerful tool in this transition, providing real fuel savings, emissions reductions, and regulatory advantages. But how much impact do they really have?

Fuel Savings and Efficiency Gains

Wind propulsion is not a theoretical concept—it is already delivering measurable fuel savings. Verified data from shipowners and operators shows that WAPS can reduce fuel consumption by 5-20% annually, with some vessels exceeding 30% savings in optimal conditions. These reductions depend on several factors, including the type of WAPS installed, the vessel’s size, its operational route, and prevailing wind conditions.

For ships operating on wind-friendly routes, the benefits can be even greater. Weather routing, a navigation strategy that optimizes voyages based on wind patterns, can amplify fuel savings by steering ships into favorable conditions. Optimized routing can sometimes double the fuel savings compared to a direct, non-optimized path. This means that shipowners who integrate WAPS reduce operational costs and gain a strategic advantage by minimizing fuel dependency in an era of volatile prices.

Emissions Reduction and Environmental Impact

The environmental benefits of WAPS go beyond just reducing carbon dioxide (CO₂) emissions. By tapping into an inexhaustible, zero-emission energy source, WAPS help ships cut their greenhouse gas footprint, supporting industry-wide decarbonization goals.

Beyond CO₂ reductions, WAPS also play a role in minimizing underwater radiated noise (URN), which can disrupt marine ecosystems, particularly for species that rely on echolocation. Studies have shown that by decreasing reliance on traditional propulsion, WAPS reduce cavitation noise and propeller loading, making voyages quieter and less disruptive to marine life.

With regulatory bodies like the International Maritime Organization (IMO) and the European Union (EU) imposing stricter emissions targets, ships with WAPS gain a competitive edge in compliance. By lowering fuel consumption, WAPS directly contribute to meeting the Energy Efficiency Existing Ship Index (EEXI) and Carbon Intensity Indicator (CII) targets, while also easing compliance with carbon pricing mechanisms like the EU Emissions Trading System (EU ETS).

Achieving Compliance at Sea with WAPS Technology

The regulatory landscape for maritime emissions is rapidly evolving. WAPS are not just an optional upgrade—they are becoming a strategic necessity for compliance and cost reduction.

IMO Regulations

The Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing Ship Index (EEXI) set efficiency benchmarks for both new and existing vessels. By reducing fuel consumption, WAPS directly enhance a ship’s efficiency rating, making it easier to meet increasingly stringent IMO targets.

Another key metric is the Carbon Intensity Indicator (CII), which measures emissions per transport capacity. Ships that fail to meet CII thresholds must submit corrective action plans, and WAPS can play a crucial role in preventing rating downgrades by improving fuel efficiency year after year.

Looking ahead, the IMO is preparing new decarbonization regulations for 2027, which are expected to introduce even stricter limits on fossil fuel use and emissions. Ships that invest in wind propulsion today will be better positioned to comply with these future rules, avoiding costly retrofits or operational restrictions.

EU Regulations

The European Union is pushing aggressive decarbonization policies through the EU Emissions Trading System (EU ETS) and the FuelEU Maritime Regulation.

From 2024, ships over 5,000 GT operating in EU waters must purchase carbon credits to offset their CO₂ emissions. Since WAPS reduce fuel consumption, they also reduce emissions—directly lowering the number of credits a shipowner needs to buy. This translates to immediate financial savings, making wind propulsion an attractive investment.

The FuelEU Maritime Regulation, taking effect in 2025, goes even further by introducing well-to-wake greenhouse gas (GHG) intensity limits. Ships using WAPS receive reward factors of 1%, 3%, or 5%, which improve compliance scores and reduce penalties. Since these rewards have no expiration date, WAPS-equipped vessels maintain a lasting regulatory advantage.

WAPS Challenges and Safety Considerations

While WAPS offer significant advantages in fuel savings and emissions reduction, integrating them into ship designs presents challenges, particularly regarding classification, structural integrity, stability, and operational safety. The absence of comprehensive IMO regulations specific to WAPS has led classification societies like ABS and DNV to develop dedicated rules and notations, ensuring that these technologies are implemented safely and efficiently.

ABS and DNV: Establishing Standards for WAPS

Two of the world’s leading classification societies, ABS (American Bureau of Shipping) and DNV (Det Norske Veritas), have introduced structured frameworks for WAPS installations. These frameworks provide mandatory classification requirements and optional notations, helping shipowners integrate wind propulsion systems while ensuring compliance with maritime safety regulations.

ABS Requirements for Wind-Assisted Propulsion Systems

ABS has established the Requirements for Wind-Assisted Propulsion System Installation, replacing its previous “Guide” to reflect mandatory classification criteria for vessels seeking certification. The document outlines installation, design, and operational requirements for two primary wind propulsion technologies: Flettner rotors and wing sails (including both rigid and soft sails). These systems, are recognized by the IMO’s Energy Efficiency Design Index (EEDI) under MEPC.1/Circ. 815, provide verified fuel savings by reducing a ship’s main engine power requirements.

Unlike conventional sails, modern wind-assisted propulsion systems incorporate automatic control mechanisms to optimize thrust generation based on wind conditions. This increases efficiency while reducing windage area and operational complexity. As technology continues to evolve, ABS allows for alternative designs and technologies, provided they can demonstrate compliance through engineering validation or proven service experience.

ABS has also introduced two class notations:

• Wind-Assisted – Ensures vessel safety when WAPS is installed.
• Wind-Assisted+ – Covers both vessel and system safety, including machinery integration.

Additionally, ABS has established the Wind-Assisted Ready notation, enabling shipowners to prepare newbuilds for future WAPS installation with pre-fitted structural reinforcements and system interfaces.

DNV’s WAPS Classification and Notations

Similarly, DNV has developed DNV-ST-0511, a dedicated standard that provides a certification framework for wind-assisted propulsion technologies. Unlike ABS, which focuses on Flettner rotors and wing sails, DNV’s standard applies broadly to various WAPS types, including suction sails and kites.

DNV also offers two key notations:

• WAPS – Covers ship-specific installation safety, including structural integration, stability, and navigational impact.
• WAPS Ready – Allows shipowners to prepare vessels for WAPS installation at a later stage, minimizing future retrofitting costs.

Both ABS and DNV emphasize that structural modifications, stability considerations, and operational adjustments are essential for the safe deployment of WAPS. These classification frameworks provide shipowners with clear regulatory pathways, reducing uncertainty and streamlining WAPS adoption.

Structural, Stability, and Operational Challenges

From an operational perspective, WAPS impact a vessel’s stability, maneuverability, and visibility. Large sail structures may obstruct the bridge’s line of sight, interfere with radar performance, or create additional stress on the deck. Shipowners must conduct comprehensive feasibility assessments to ensure that deck reinforcements can handle dynamic wind loads, particularly for retrofit installations.

Ports and narrow waterways may also impose height restrictions, requiring retractable or tiltable WAPS designs. Additionally, certain navigation and emergency protocols may need adjustments, particularly regarding manoeuvrability in congested waters and compliance with existing COLREGs and SOLAS regulations.

With ABS and DNV now providing structured certification pathways, shipowners have a clearer roadmap for WAPS adoption. However, as wind propulsion technology evolves, further refinements in global safety regulations will be necessary to ensure seamless integration across the maritime industry.

WAPS Case Studies and Real-World Impact

Short-Sea Vessel (EU Route)

A short-sea cargo ship operating in European waters installed one to three suction or rotor sails, depending on the case study scenario. Over a projected timeframe from 2026 to 2044, these installations delivered fuel savings that translated into annual cost reductions of 4% to 12%. The vessel also benefited from lower EU ETS compliance costs, making the investment financially attractive.

Deep-Sea Cargo Ship

For deep-sea shipping, where fuel consumption is highest, WAPS showed even greater potential. A case study of a long-haul cargo ship demonstrated significant emissions reductions, directly lowering the ship’s carbon compliance costs under both the IMO and EU regulatory frameworks. The ability to operate on lower emissions thresholds without switching to expensive alternative fuels provided a strong economic incentive for WAPS adoption.

The Future of WAPS: Where Is the Industry Heading?

Momentum for wind propulsion is growing rapidly. More shipowners and operators are recognizing the long-term benefits of harnessing free, renewable energy, and regulatory bodies are increasingly providing incentives for early adopters.

Shipyards are responding to this trend by developing “WAPS-ready” newbuilds, designed to accommodate wind propulsion from day one. Meanwhile, technology providers are scaling up production, improving the efficiency and affordability of WAPS solutions.

The future will also bring advancements in verification methods, ensuring more accurate performance assessments for ships using wind propulsion. With robust data proving the cost and emissions benefits, financial institutions may soon start offering green financing incentives for WAPS-equipped vessels.

At the policy level, stronger carbon pricing mechanisms and emissions trading schemes will make fuel efficiency even more critical. Ships that invest in WAPS today will have a built-in advantage as these regulations tighten.

Is WAPS the Right Investment for Your Fleet?

For shipowners looking to future-proof their fleets, WAPS is one of the most practical and scalable solutions available today. It offers a proven track record of fuel savings, reduces compliance costs, and positions vessels ahead of incoming regulations.

The maritime industry is on the verge of a wind-powered renaissance—one that blends modern engineering with one of the oldest forms of propulsion. Investing in WAPS is not just about sustainability; it’s about staying competitive in an industry where efficiency, cost savings, and emissions reduction define success.

The question isn’t whether WAPS will play a role in shipping’s future—it’s whether your fleet will be ready to capitalize on it.