The maritime industry faces growing pressure to reduce greenhouse gas (GHG) emissions and transition toward sustainable propulsion technologies. This thesis investigates the feasibility of employing ammonia and hydrogen as alternative fuels in dual-fuel configurations with diesel for large two-stroke internal combustion engines (ICEs). A voyage simulation model of a post-Panamax container ship (the Duisburg Testcase) was developed in MATLAB Simulink to evaluate fuel performance under voyage conditions. The research includes a review of the properties of ammonia and hydrogen, the development of dualfuel engine models based on the Seiliger process, and the integration of these models into a timedomain voyage simulator. Simulations were performed for diesel, diesel–ammonia, and diesel–hydrogen operation to compare fuel consumption and efficiency. Results show that both ammonia and hydrogen can be more energy efficient relative to conventional diesel operation. Ammonia offers promising scalability and easier storage, while hydrogen achieves higher efficiency but presents greater challenges regarding storage and safety. The developed simulation framework provides a tool for evaluating and optimizing dual-fuel propulsion systems, supporting the maritime sector’s transition to cleaner energy solutions.