Wind propulsion for commercial cargo ships is rapidly emerging as a viable technology to reduce greenhouse gas emissions. Naval architects frequently adapt methods and tools originally designed for sailing yachts to create these modern "sailing" vessels. Typically, steady-state Performance Prediction Programs (PPPs) are used to estimate vessel speed, leeway, heel, and other factors under various wind conditions. However, these tools do not account for dynamic factors such as unsteady sail forces due to ship motions in waves, gusty winds, or the vessel’s control system dynamics. This paper presents a comparative analysis of control algorithms and their impact on the performance of a wind-powered cargo vessel. We utilize a Dynamic Performance Prediction Program (DPPP) that integrates an unsteady 3D fully nonlinear potential flow hydrodynamic solver with an efficient lifting-line aerodynamic model. This approach allows us to assess the performance implications of different control strategies. The findings reveal how various control strategies influence sailing performance, highlighting the potential benefits and trade-offs in unsteady, real-world environmental conditions. .

This paper presents findings of the Horizon Europe project OPTIWISE, which focuses on developing innovative design methods for ships equipped with wind-assisted propulsion. The project encompasses comprehensive evaluations, including environmental, economic, and business impacts. Three distinct design cases are explored: a bulk carrier using Rotor Sails, a tanker fitted with Oceanwings, and a passenger vessel with Solid Sails. The wind-assisted propulsion systems are detailed, along with the design and evaluation methodologies employed. Rotor Sails harness the renewable power of wind through the Magnus effect, significantly reducing fuel consumption and emissions. Oceanwings provide additional thrust to vessels. Solid Sails, a modern take on traditional sails, are constructed using advanced materials and have versatile applications. OPTIWISE also introduces innovative design and evaluation methods that consider the holistic impact of wind propulsion on ship design. The need for a more integrated approach is emphasized, where all relevant subsystems are evaluated and optimized together, considering the full operational conditions. As the shipping industry journeys towards sustainability, wind-assisted propulsion systems offer a promising solution. OPTIWISE’s insights and methodologies contribute to the adoption of these innovative technologies, fostering a greener and more efficient future for maritime transport.

This paper discusses the impact of scaling effects in the performance of a standalone wing sail, comparing experiments and numerical simulations. The experimental data of a standalone wing sail with a NACA0015 section, tested in the R.J. Mitchell wind tunnel at the University of Southampton, are compared with wind tunnel tests run at KTH Royal Institute of Technology, where the L2000 wind tunnel and wing sail had a smaller scale, and with Computational Fluid Dynamics simulations of three different cases. For the numerical simulations, first the model scale Southampton wind tunnel was simulated. Then, keeping the same scale, the wind tunnel domain was substituted with a larger domain to simulate an open-field condition, and analyse the presence of blockage effects. Finally, full-scale simulations were achieved keeping the same scale of the model scale open-field simulations, and reaching the full-scale Reynolds number by varying the viscosity of the fluid. The flow in the numerical simulations is modelled with the RANS equations and the k − ω SST turbulence model, knowing about its limitations in simulating stall conditions, but judged to be satisfactory for a preliminary study about scale effects. The range of model scale Reynolds numbers covered by both experimental campaigns spans from 2.2x105 to 6.7x105, while the full-scale Reynolds number is equal to 7.9x106, covering a range representative of most wind propulsion technologies. The main conclusions are that the simulations capture well the shape of the lift curve up to an angle before stall, after which the simulations diverge from the experiments. In full-scale, higher lift coefficients are reached, and the lift curve shows a different behaviour than in model scale, with a longer linear region and a more abrupt stall. © 2025 CSYS. All rights reserved.

International regulations on greenhouse gas (GHG) emissions as well as strong market demand for zero-emission transport calls for a radical change in the shipping industry. Measures such as hull form optimization, use of alternative fuels and efficient machinery systems, new coatings, and smart routing have already improved the energy efficiency of the world fleet. However, it is far from enough. To effectively respond to the climate challenges, we must turn to emission-free energy sources. One such promising and well-proven zero-emission propulsion system for shipping is wind propulsion. Using wind to power cargo vessels re-started on a commercial scale about a decade ago and there are today more than 50 wind-assisted vessels in commercial trade or under construction. They are equipped with a variety of wind propulsion technologies like Flettner rotors, wing sails and kites, which may give fuel and emission reductions of up to about 20%. With the goal of demonstrating that even higher energy and emission reduction is feasible, 11 representatives of the European maritime industry and research community have recently joined forces in the large-scale EU-funded project Orcelle, led by Wallenius Wilhelmsen Ocean. The present paper outlines the project’s ambition, scope of work and expected outcome.

Computational Fluid Dynamics (CFD) simulations to predict forces from a Wind Propulsion Unit (WPU) on a ship hull are carried out to better understand the forces dependency on wind speed and angle. Three different Atmospheric Boundary Layer (ABL) stratifications, nominally unstable, neutral, and stable, are studied in a CFD environment to better understand how to reproduce these velocity profiles numerically and how much is their impact on the performance of a general ship’s hull equipped with a Flettner rotor. A series of 2D and 3D simulations with an empty domain are run to tune some numerical settings for a correct representation of the ABL. Simulations with a simplified hull and a Fletter rotor are run to purely analyse the differences between the profiles and their effects on a reproduceable geometry. The three different ABL profiles are tested for four different wind angles, producing an overview of the dependency of rotor and ship performance on wind speed profiles, wind angles and hull interaction. A clear impact of the wind profiles and the wind angle on the ship hull is visible on the rotor lift and drag coefficients, while in terms of ship performance, described by the ratio of the thrust and side force coefficients, the impact is limited

The need to reduce green-house gas emissions has renewed the interest in wind propulsion for commercial cargo vessels. When designing such modern “sailing” ships, naval architects often lean on methods and tools originally developed for the design of sailing yachts. The most common tool today is the steady-state Performance Prediction Program (PPP), typically used to predict quantities like speed, leeway, heel of the vessel when sailing in a range of wind directions and wind speeds. Steady state PPPs are very efficient and can be used to rapidly assess a large number of design alternatives. PPPs are, however, not able to consider dynamic effects such as unsteady sail forces due to ship motions in waves or the turbulent structure of the natural wind. In this paper we present time-domain simulations with a Dynamic Performance Prediction Program (DPPP) that can take the “unsteadiness” of the natural environment into account. The program is based on coupling an unsteady 3D fully nonlinear potential flow hydrodynamic solver to an efficient lifting-line aerodynamic model. Particular attention is paid to a recently implemented unsteady aerodynamic model that employs an indicial response method based on Wagner’s function. The usefulness of such advanced simulations for performance prediction in moderate environmental conditions is investigated for a wind-powered cargo vessel with wing sails. Control system strategies such as sheeting of the wing sails close to stall are studied.

Rapid performance prediction tools are required for the evaluation, optimization, and comparison of different wind propulsion systems (WPSs). These tools should capture viscous aerodynamic flow effects in 3D, particularly the maximum propulsion force, stall angles, and interaction effects between the lift-generating units. This paper presents a rapid aerodynamic calculation method for wing sails that combines a semi-empirical lifting line model with a potential flow-based interaction model to account for 3D interaction effects. The method was applied to a WPS that consisted of several wing sails with considerable interaction effects. The results were compared to CFD RANS simulations in 2D and in 3D. For the evaluated validation cases, the interaction model improved the prediction considerably compared to when the interaction was not accounted for. The method provided acceptable driving force, moments, and stall predictions, with negligible computational cost compared to 3D CFD simulations. 

Wind propulsion technology for modern cargo vessels has developed from non-existing to a viable industry in a few years and it is expected to expand further before the decade is out. This calls for standardisation of methods and terminology. A specialist committee under the International Towing Tank Conference (ITTC) is currently developing guidelines for performance indicators, performance prediction methods and sea trial methods for wind assisted ships. This paper outlines the scope and methodology of the draft guidelines. 

Shipping is a critical component of global trade but also accounts for a substantial portion of global greenhouse gas emissions. Recognising this issue, the International Maritime Organisation (IMO) has implemented new measures aimed at determining the energy efficiency of all ships and promoting continuous improvements, such as the Energy Efficiency Existing Ship Index (EEXI). As Computational Fluid Dynamics (CFD) can be used to calculate the EEXI value, RISE-SSPA1 and Flowtech have developed a CFD-based method for predicting full-scale ship performance with SHIPFLOW v7.0, which meets the new requirements of IMO. The method is validated through an extensive comparison study that examines the delivered power and propeller rotation rate between full-scale CFD predictions and high-quality sea trials using 14 common cargo ships of varying sizes and types. The comparison between the CFD predictions and 59 sea trials shows that both delivered power and RPM can be predicted with satisfactory accuracy, with an average comparison error of about 4% and 2%, respectively. The numerical methods used in this study differ significantly from the majority of the state-of-the-art CFD codes, highlighting their potential for future applications in ship performance prediction. Thorough validation with a large number of sea trials is essential to establish confidence in CFD-based ship performance prediction methods, which is crucial for the credibility of the EEXI framework and its potential to contribute to shipping decarbonisation.

Wind-powered ship propulsion (WPSP) is the concept where the wind is the main source of thrust, while the traditional propulsion system operates when needed. This type of propulsion can lead to considerably reduced emissions, something that the shipping community is striving for. A well-known example of WPSP is the Oceanbird with the goal to cut emissions of up to 90%. In this study, the propeller design process for a wind-powered car-carrier (wPCC) such as the Oceanbird is investigated, what the various challenges of WPSP are and therefore how an automated optimisation procedure should be approached. A controllable-pitch propeller was selected as suitable propeller type for the operation of the wPCC, and various functions such as windmilling, feathering and harvesting have been explored. Regarding the optimisation procedure, an essential input is the definition of the operational profile, in order to determine the most important conditions for the route. The main objective of the optimisation is the minimisation of the total energy consumption (TEC), calculated based on a selection of conditions using the potential flow solver MPUF-3A. Cavitation has been evaluated by the blade designer, through an interactive optimisation method. The results showed that designing and optimising for the most highly loaded condition led to solutions with the lowest TEC. © 2022 The Author(s)