Ship energy efficiency and maritime decarbonization: A comprehensive review of technologies,regulations and emerging solutions

This review presents a comprehensive examination of ship energy efficiency strategies in the context of maritime decarbonization imperatives. It synthesizes current technological advancements, regulatory frameworks, and fuel alternatives that aim to reduce greenhouse gas (GHG) emissions in alignment with international mandates, particularly those issued by the International Maritime Organization (IMO) and regional bodies. The review categorizes the evaluated measures into seven principal domains: internal combustion engines and alternative fuels, carbon capture and storage (CCS) systems, cold ironing (shore power connectivity), waste heat recovery systems (WHRS), air lubrication systems (ALS), solar and wind energy applications, integration of batteries and fuel cells, nuclear energy and other technologies. Each category is critically assessed in terms of its technological maturity, retrofit potential, operational feasibility, economic viability, and environmental impact. The analysis reveals that while mature technologies like WHRS and dual-fuel engines offer short-term benefits, more disruptive innovations such as fuel cells and hybrid propulsion systems remain constrained by cost, infrastructure, and safety concerns. The review highlights the growing prominence of hybrid and integrative configurations, such as WHRS coupled with CCS or wind-assisted propulsion integrated with route optimization algorithms, as promising pathways for maximizing efficiency and reducing emissions. Ultimately, this review serves as a decision-support resource for ship owners, marine engineers, and policymakers. By mapping out the trade-offs and synergies among diverse technologies, it provides a nuanced foundation for aligning strategic investments with evolving decarbonization targets and operational realities in the global maritime sector.