Alternative fuels and design modifications for environmentally sustainable marine vessels

The maritime industry faces significant challenges in reducing greenhouse gas emissions while maintaining operational efficiency. This paper assesses four major alternative marine fuels—liquified natural gas (LNG), hydrogen, methanol, and ammonia—and the required ship modifications. The evaluation follows International Maritime Organization life cycle assessment guidelines and the Energy Efficiency Existing Ship Index (EEXI), highlighting design changes that can reduce emissions. Findings indicate that polymer bearings in propulsion systems are 6–9 times more efficient in reducing friction power loss than traditional metal bearings. Integrated energy recovery systems can generate an additional 15–17 % of net power. Sustainability analysis shows that hydrogen and LNG can be considered the most suitable options environmentally, economically, and operationally. Hydrogen-powered systems could reduce maritime CO 2 emissions by up to 70 % by mid-century, with fuel cells offering 75 % energy conversion efficiency, compared to 55–60 % for conventional diesel engines. However, challenges such as infrastructure, safety concerns, and high investment costs remain. These issues require collaborative efforts from the industry and regulators. This research contributes to maritime sustainability by providing quantitative performance data and strategies for adopting alternative fuels in both new and existing fleets. • Novel sustainability assessment framework reveals hydrogen and LNG achieve highest sustainability index (2.8/4.0). • Hydrogen PEMFCs demonstrate 75 % energy efficiency versus 55–60 % in traditional diesel vessels. • Ship modifications with polymer bearings reduce power loss by 6–9 times in container ships. • Maritime industry could reduce emissions by 40 million tons through alternative fuel adoption. • Kriso Very Large Crude Carrier (KVLCC2) hull modifications with water flow turbines generate 15–17 % additional net power.