Hydrogen fuel presents a promising pathway for achieving long-term decarbonization in the maritime sector. However, its use in diesel engines introduces challenges due to high reactivity, leading to increased NOx emissions and combustion instability. The aim of this study is to identify settings so that the investigated engine operates with 60% hydrogen energy fraction at high load through CFD modelling. The model is utilized to simulate a four-stroke, 10.5 MW marine engine at 90% load, incorporating 60% hydrogen injection by energy at the engine intake port. The CFD model is verified using experimental data from diesel operation of the marine engine and hydrogen operation of a light-duty engine. The engine performance was determined and detailed emissions analysis was conducted, including NO, NO₂, HO₂, and OH. The findings indicate a substantial rise in NOx emissions as opposed to diesel operation, due to elevated combustion temperatures and increased residence time at elevated temperature of the mixture in-cylinder. The presence of HO₂ and OH highlights critical zones of combustion, which contribute to operational stability. The novelty of this study is supported by the examination of the high hydrogen energy fraction, the advanced emissions analysis, and the insights into the emissions–performance trade-offs in hydrogen-fueled dual-fuel marine engines. The results offer guidance for the development of sustainable hydrogen-based marine propulsion systems.