We analyze the elements determining the sustainability of nautical tourism in selected Mediterranean countries (Croatia, Slovenia, Greece, Italy and Turkey). The purpose of our research is to investigate the main obstacles to greater application of renewable energy sources (RES) as the basis for the sustainability of nautical tourism. The obtained results provide valuable information that can help companies and policy makers choose appropriate strategies to achieve the EU 2030 sustainability goals in this sector. Our survey among charter companies was conducted during 2018 on a sample of 51 respondents. We conclude that there is a serious lack of knowledge among nautical tourism respondents regarding the availability of financial instruments from EU funds intended for increasing energy efficiency and adoption of RES. Respondents were familiar with general measures to reduce energy costs but are not familiar with the measures and opportunities provided by available European funds. Our results confirm previous research indicating that significant savings in energy consumption can be achieved by using RES (especially photovoltaic (PV) modules) and that insufficient financial resources and lack of knowledge are the main obstacles to achieving higher adoption rates of RES and increasing energy efficiency in nautical tourism.