Hydrodynamic and environmental impact assessment of gulet yachts using alternative fuels along the blue voyage route

As iconic vessels of the Aegean and Mediterranean coasts, gulets play a central role in Blue Voyage, presenting a valuable opportunity for advancing sustainable marine tourism through cleaner propulsion solutions. This study investigates the hydrodynamic performance and environmental impacts of two Bodrum Gulet-type hull forms, with overall lengths of 24 and 33.8 m, through Computational Fluid Dynamics (CFD) analyses and environmental sustainability assessments. The hydrostatic characteristics of the modeled hulls are determined, and flow characteristics, total resistance, and power requirements are evaluated. A case study based on a typical Blue Voyage route is conducted to evaluate the environmental implications of operating gulets with marine diesel oil (MDO), liquefied natural gas (LNG), and methanol (MeOH). Emission Ratio (ER) and Energy Efficiency Index (EEI) are calculated to quantify the performance of each fuel type. Results show that the current gulet hull forms can be optimized to reduce total resistance, enhancing the feasibility of adopting alternative fuels. The use of LNG and MeOH can lower CO₂ emissions by up to 9.8 % and 15.8 %, respectively, compared to MDO, with corresponding reductions in EEI of 8.3 % and 12.3 %. In addition, these benefits are found to be more pronounced for larger gulets operating at high occupancy levels. While LNG and MeOH offer notable environmental advantages, their application to gulets presents significant challenges, such as increased space requirements, safety considerations, and retrofitting constraints, making them more appropriate for new constructions or long-term planning.