The increasing interest in air pollutant emissions reduction also influences the shipbuilding industry. In this sense, hybrid-electric propulsion is a promising solution for green navigation, ensuring a Zero Emission Mode navigation close to coastal areas and harbors. Hybrid-electric propulsion is a convenient choice not only for new units but also for the retrofitting of outdated ones. This paper deals with an example concerning the retrofitting of a small passenger vessel, where the study of the application of hybrid-electric systems was possible only thanks to reverse engineering techniques for the identification of the internal spaces. The final hybrid configuration refers to a slow-tourism operative profile in the North Adriatic area.