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Abstract: Growing requirements from regulations regarding energy efficiency lead to innovative machinery layouts. A recent trend tends towards hybrid ship drive systems. While these systems may offer a large potential, a thorough analysis is needed as this potential is strongly dependent on the intended purpose, thus on the operational profile. Especially since the additional investment costs have to be recouped through savings in the operation or lower installed power capacity, those systems need to be accurately examined. The early fixing of costs in shipbuilding projects, leads to the necessity of an early and precise evaluation of the drive systems efficiency. The ideal dimensioning of the components of hybrid drive systems determines the actual added value of such a system regarding reduction of emissions and savings of operational costs. In this paper a method for dimensioning hybrid ship power systems with electrical propulsion is introduced. A key importance of the method is using only basic input parameters available in the early design stage, while producing sufficient results for optimal dimensioning. The method uses time series or cumulative density function of the power as input data. Different system configurations can be assessed and compared. The optimal load distribution on the different power suppliers is implemented with a rule-based approach and orientates towards maximum efficiency within the systems technical and specified constraints. For the comparison of different systems, the method provides cost and system relevant results. This includes the fuel consumption, operating hours, state of charge and load cycles for lifetime calculations of the battery.