Operational Guide · Registers & Logbooks

# Wind-Assisted Propulsion Systems (WAPS)

Rotor sail, wing sail, suction sail or kite: every ton of fuel saved by an auxiliary wind propulsion system is simultaneously a cost saving, a CII improvement, and an avoided compliance cost.

WAPS rotor sail wind propulsion CII decarbonization

## Operational Explanation

Wind-Assisted Propulsion Systems (WAPS) are devices that harness wind energy to supplement a ship's main propulsion, reducing fuel consumption and emissions. The main technologies include Flettner rotors, rigid wing sails, soft sails, suction sails and towing kites. Achievable fuel savings range from 5% to 30% depending on the technology, ship type and the route's wind conditions.

The global WAPS market reached USD 1.34 billion in 2024, with retrofit installations accounting for over 60% of the market: the technology is therefore spreading significantly on the existing fleet as well, not just on new builds. The number of installations passed the 100-unit threshold in 2025, and the IMO has defined a dedicated work plan on wind propulsion to encourage its broader adoption.

## Regulatory Reference

There is no single IMO instrument dedicated to WAPS; the IMO has nonetheless defined a specific work plan on wind propulsion to encourage its adoption, and the benefit of WAPS is reflected indirectly in existing measures: every ton of fuel saved directly improves the ship's CII rating under MARPOL Annex VI.

## Scope of Application

Ships installing auxiliary wind propulsion devices (Flettner rotors, rigid or soft sails, suction sails, towing kites) to supplement main propulsion, both in new construction and as a retrofit on existing ships.

## Procedure / How to Complete It

1. Assess the WAPS technology best suited to the ship type and planned operating routes, considering that fuel savings depend heavily on the specific route's wind conditions.
2. Verify the operational impacts of the installation (stability, visibility from the bridge, interference with loading/discharging operations) before finalizing the technology choice.
3. Train the crew on operational management of the installed WAPS system, including procedures for folding/securing it in adverse weather or during port operations.
4. Integrate the WAPS contribution into route planning, optimizing the ship's positioning relative to expected wind conditions when possible.
5. Systematically monitor the actual fuel savings achieved by the WAPS system to verify its real impact on the ship's CII rating.

## Practical Example

Example: a dry bulk ship installs two Flettner rotors in a retrofit configuration, achieving an estimated fuel saving of between 5% and 15% depending on the route; the crew is trained on the procedure for securing the rotors in extreme wind conditions and during port loading operations.

## Real Cases

The WAPS market has seen significant growth, surpassing 100 global installations in 2025, driven largely by retrofit projects on existing ships (over 60% of the market); a Chinese project also unveiled in 2026 the largest auxiliary wind propulsion system ever installed on a ship, confirming the acceleration of adoption of this technology as a low-technological-risk decarbonization lever compared to more experimental solutions such as ammonia or hydrogen.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
WAPS technology chosen without a specific assessment of the wind conditions on the ship's actual operating routes | Actual fuel savings significantly below expectations | Always assess the specific wind conditions of planned operating routes before choosing the WAPS technology
Crew not adequately trained on procedures for securing the WAPS system in adverse weather conditions | Operational risk during extreme wind events or rough seas | Systematically train the crew on management and securing procedures for the specific WAPS system installed
Operational impacts of the installation (bridge visibility, interference with loading operations) not assessed before the technology choice | Operational complications discovered only after installation | Assess all relevant operational impacts before finalizing the choice of technology and its placement on board

## PSC Observations

WAPS are not typically subject to direct PSC verification, but their correct integration into route planning and consumption monitoring can be relevant for verifying the consistency of reported SEEMP/CII data.

## Operational Tips

- Always assess the specific wind conditions of actual operating routes before choosing the WAPS technology, rather than relying on generic industry averages.
- Systematically train the crew on management and securing procedures for the specific WAPS system installed on board.
- Integrate the WAPS contribution into route planning where possible, to maximize achievable fuel savings.

## Checklist

- WAPS technology assessed in relation to the wind conditions of actual operating routes
- Operational impacts (stability, visibility, interference with loading/discharging) verified before installation
- Crew trained on operational management and securing of the system
- WAPS contribution integrated into route planning where possible
- Actual fuel savings systematically monitored for their impact on the CII rating

## FAQ

How much fuel is saved with a WAPS system?
From 5% to 30% depending on the technology, ship type and route wind conditions; Flettner rotors in particular report average savings of between 5% and 25%.
Can WAPS only be installed on newly built ships?
No: over 60% of the current WAPS market consists of retrofit installations on existing ships, not just new construction.
How does WAPS affect the ship's CII rating?
Every ton of fuel saved thanks to the WAPS contribution directly improves the ship's CII rating, in addition to reducing fuel cost and exposure to other emissions-based compliance mechanisms.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

CII (Carbon Intensity Indicator)Operational Energy Efficiency in the Engine Room

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