To mitigate the environmental impact of shipping on climate change, it is nowadays urgent to explore energy efficiency and cost-effective measures by means of reliable digital tools. These are becoming essential for assisting the design of new ships and the refurbishment of the existing ones, as well as for assessing and optimizing the energy performance of a ship during its entire life-cycle. This paper focuses on the verification of the reliability of a novel ship energy dynamic simulation tool, developed for the calculation of the energy, economic, and environmental performance of large ships, the design and optimization of energy system layouts and operational logics, as well as the definition of design and management guidelines for ships. The reliability of the developed model was verified through the use of data measured onboard an existing cruise ship. The verification procedure is conducted for assessing the reliability and for exploiting the potential of dynamic analysis for a more precise evaluation of ships loads, temperature levels, and necessary sizes of technologies. The validate tool will enable reaching two different goals: i) to evaluate different energy system layouts to define the optimal one to achieve imposed targets, ii) to obtain a large amount of data that can allow the implementation of the digital twin in the maritime sector. The developed model relies on several well-established software to assess the energy, economic and environmental performance of different types of ships. The model validation was successfully assessed and very low or negligible deviations, lower than 4%, of numerical data from measurements were observed. Thanks to the validated simulation model it was possible to assess the energy performance of the investigated ship, that requires approximately 23.4 GWh of primary energy from polluting fuels over two weeks. The model provided insights into the flow rate, temperature levels, and energy flows of the ship energy system, necessary for identifying the amount of thermal energy to be recovered and potential solutions to enhance the efficiency of the entire system.