Wind-Assisted Propulsion Systems (WAPS)
WAPS can reduce propulsion power and fuel use in favourable conditions, but benefit depends on the ship, route, wind, arrangement and auxiliary loads and must be verified against a comparable baseline.
Operational Explanation
Wind-Assisted Propulsion Systems include rotors, rigid or soft sails, suction sails and kites that provide part of the thrust. Performance depends on the ship, installation, route, wind, sea state, speed and operating strategy.
Supplier estimates or results from other ships are not guaranteed performance. The balance must include auxiliary demand, added resistance, unavailability, route deviations and comparable conditions. Any CII or cost effect follows only from verified results and the applicable methodology.
Regulatory Reference
MEPC.1/Circ.896 — EEDI/EEXI, innovative technologies; IMO — current MARPOL Annex VI methodologies. The guidance addresses WAPS in EEDI/EEXI calculation and verification; it does not establish a universal operational savings percentage. Installation safety approvals remain distinct from energy assessment.
Scope of Application
Newbuilds and retrofits for which ship type, route profile, wind conditions and operational constraints make the system technically assessable. Suitability and benefit must be demonstrated for the specific project.
Procedure / How to Complete It
- Define the baseline, metric and comparable conditions.
- Assess wind and route together with speed, stability, structure, visibility and cargo operations.
- Include auxiliary demand, resistance, availability and operating limits in the balance.
- Obtain applicable approvals and train the crew.
- Measure the result, normalize the data and review assumptions.
Practical Example
A bulk carrier assesses a rotor retrofit using its own route, checks stability and cargo operations, then compares normalized fuel use before and after installation including system loads. The documented result, rather than a commercial percentage, supports the business case.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Saving transferred from another ship | Unreliable business case | Use the ship’s own route, arrangement and baseline |
| Main-engine fuel considered alone | Net benefit overstated | Include all loads and losses |
What the PSCO Checks
Operational Tips
- Separate the EEDI/EEXI design contribution, measured in-service consumption and CII result; apply the relevant methodology to each.
- Retain baseline, wind, route, speed, auxiliary loads and normalization criteria, distinguishing measurements from simulations.
- Include operating limits and securing arrangements in onboard procedures; check interference with visibility and port operations.
Preparation checklist
- Baseline and metric defined
- Representative route and wind data used
- Loads and losses included
- Approvals and procedures available
- Performance measured and normalized
FAQ
Related Topics
Last substantive revision of this page: 15 September 2026 · page fingerprint 1d8a49229e4b