Classification society DNV has released an update to its Wind Assisted Propulsion Systems technical standard ST-0511. The major update introduces new methods for evaluating WAPS fatigue strength, as well as the performance of the systems in extreme conditions. Wind Assisted Propulsion systems WAPS are one of the most promising measures to assist the decarbonization of shipping. Wind is an inexhaustible, free, zero carbon energy source and a combination of advanced aerodynamics, automation, computer modelling, and new materials are unlocking a new generation of innovative wind systems.While experience in using the systems is still developing, WAPS have already been implemented on commercial vessels and can enable fuel savings of up to 20%. The new updates to DNV’s industry leading technical standard ST-0511 will support the growing interest in WAP systems as the industry looks to enhance sustainability and reduce fuel consumption in a tightening regulatory and economic climate.The interaction of WAPS with the structure of a vessel’s hull can be quite complex, so the update features a comprehensive new section on fatigue strength, including calculations that offer a completely new approach to derive the load combinations from the wind and inertia forces on WAP systems. In addition, the standard sets out a new approach to assessing how WAPS perform under extreme wind conditions. Finally, the documentation requirements have been adjusted to streamline the process. The WAPS ST-0511 standard provides a framework for the verification and certification of wind assistance propulsion systems. It can be applied in obtaining an Approval in Principle, a Design approval or a Type approval. These verifications and certifications can also be obtained as part of the integration into a vessel or independently. The ST-0511 technical standard is a complement to the DNV WAPS class notation, which is focussed on the integration of systems onboard vessels, whether retrofitted or as part of a newbuilding.