In this article, the mapping of the performance and emission parameters of a merchant vessel propulsion system over the ship operating envelope was carried out by using a model capable of representing the ship propulsion system behaviour. The model was developed based on a modular approach and was implemented in the MATLAB/Simulink environment. The various parts of the propulsion engine as well as the shafting system, the propeller and ship hull were represented by separate submodels having the appropriate interface for exchanging the required variables to each other. The output of the model includes the performance and emission parameters of the engine as well as the operating parameters of the propeller and ship. Initially, the propulsion engine operation under steady-state conditions was simulated and the predicted engine performance parameters results were validated. Then, simulations of the ship propulsion system operating points at various resistance curves were performed. Based on the derived results, the mapping of the ship propulsion system performance and emission parameters was presented and their variation throughout the ship operating envelope was discussed. Finally, an example of using the derived results in order to minimise the fuel consumption and CO2 emissions for a typical ship route is presented and discussed.