The increasing numbers of anthropogenic emissions within the maritime sector have caused growing attention for emission-reducing technologies. A promising contributor to emission-reducing ship propulsion methods is Wind-Assisted Ship Propulsion (WASP). A WASP system creates additional forward thrust, assisting the main engine during sailing. The potential impact of WASP on fuel consumption and emissions within the Boskalis fleet remains uncertain. An analysis of the Boskalis fleet is conducted to find suitable vessel types for WASP application. The results of the multiple-criteria decision analysis show that the heavy marine transport vessels are interesting vessel types for WASP. A performance analysis and a general comparison of the existing WASP technologies show that the rotor sail is a suitable technology for these vessel types. Then, a 1-degree-of-freedom steady-state and time-domain model are developed to assess the impact of rotor sails on fuel consumption and emission reductions for the Triumph. These models are developed using operational ship data and estimations of propulsive power efficiencies. Results of the steady-state model indicate that fuel and emissions reductions reach between 3.4 – 5.0% annually for a representative voyage. Results of the time-domain model indicate trip-specific savings. These results suggest that the steady-state model is more suitable for estimating annual performance, while the time-domain model is suited for evaluating specific operating conditions. The Triumph could benefit from the installation of a rotor sail to reduce fuel consumption and emissions. Further development of the model is recommended to improve the accuracy of the assessment of the operational and environmental impact of WASP systems.