This thesis investigates the yaw stability of wind-driven vessels using wingsails, addressing the urgent need for decarbonising global shipping. An analytical method is developed to assess directional stability based on aerodynamic and hydrodynamic characteristics, yielding a universal stability criterion validated with SEAMAN data. The study explores practical stability assessment approaches and evaluates the impact of varying hydrodynamic parameters, aerodynamic models, and surge coupling effects.

Results show that while stability diagnostics are invariant under different hydrodynamic models, significant variations occur in destabilised hulls. Including a boundary layer in the wind model has negligible effects on stability but increases computational effort. The closed-loop analysis assesses proportional and derivative feedback control strategies, demonstrating satisfactory stability for both human and autopilot control across all points of sail in the original hull configuration.

Time-domain responses to step rudder inputs indicate small steady errors and oscillatory components under human control, with autopilot control yielding even more robust outcomes. The study highlights the importance of surge coupling in stability analysis, often overlooked in previous models. The thesis concludes that wind-driven vessels can achieve directional stability under active control schemes, providing a foundation for future research on sustainable maritime transportation.

Due to the IMO regulations on emissions, Wind Assisted Propulsion Systems have become more and more interesting for shipowners. One of those Wind Assisted Propulsion Systems is the VentoFoil from Econowind. However, to enable the decision of the shipowner on whether and where to place VentoFoils on board, this research aimed to construct a VentoFoil Adoption model, assessing the environmental and financial consequences of specific VentoFoil placement options. With this, the main research question is: ‘What is the impact of VentoFoil placement on ships from a ship owner’s perspective?’ The VentoFoil Adoption Model for Econowind required a Technology Adoption Decision-support model that could operate within a short computational time while incorporating an adaptable weather matrix. During the literature study on the existing models regarding WASP models, a research gap was identified. The gap primarily lies in integrating low-fidelity force modelling with financial decision support.

The VentoFoil Adoption model was constructed with a baseline calculation in which no VentoFoils were placed onboard. This baseline included the hull resistance and the wind forces on the deckhouse for all possible wind directions and speeds. After that, the VentoFoils were placed on deck, for which the VentoFoil forces were added with respect to the baseline calculations. The VentoFoil forces were calculated including the interaction between the deck and the VentoFoils, using a turbulent separation layer. The interaction between the deckhouse and the VentoFoils was simulated using a triangle shape in which the wake is turbulent. Lastly, the interaction between the VentoFoils was included using a parametrized wakefield in which the apparent wind angle changed based on the distance between the VentoFoils. From the resulting polar plots, the financial and environmental benefits of VentoFoils are illustrated. Fuel savings are achieved when sailing at reference speed and lower power, and increased cargo yield is realized at higher speeds with reference power. This is dependent on the weather probability matrix.

To demonstrate the practical application and effectiveness of the model, a case study was performed using the VentoFoil Adoption Model on the Magritte, a bulk carrier currently sailing with two 16-meter VentoFoils. From a shipowner’s perspective, the conclusion was made that two 30-meter VentoFoils would in the long term be more cost-effective. For most combinations of fuel price and cargo yield, the payback time of the case at reference power and thus higher sailing speed was lower, making it the favourable operational decision.

A validation using the ‘validation square method’ was performed on the method used within the VentoFoil Adoption Model. The empirical performance validity was investigated by comparing the results from the sea trial data of the MV Sunnanvik and the results from the model. The results are within a reasonable range.

The answer to the main research question can be found with the model. Multiple placement options can be inserted, giving the benefits and costs for well-considered decision-making of the ship owner on whether and where to place VentoFoils on board.