Energy efficiency technologies for waterborne transport: A systematic review and taxonomy pathway

Abstract

Increasing pressure is being placed on maritime transport to reduce energy demand and greenhouse gas emissions within a multi-level regulatory environment. Although energy efficiency is widely recognized as a cost-effective decarbonization pathway aligned with SDG7 and net-zero objectives, policy instruments remain disproportionately oriented towards fuel substitution over demand reduction. This misalignment is compounded by the existed classification of energy efficiency technologies (EETs) for waterborne transport, which are largely descriptive and fuel-centric, lacking cross-segment comparability, standardized metrics, or simultaneous integration of technical readiness, economic feasibility, and regulatory alignment, conditions necessary for actionable decision-making under binding constraints. To address this structural gap, this study develops a decision-support framework grounded in a taxonomy pathway that bridges policy, technology, and investment perspectives, transforming technology classification into a policy appraisal tool and investment screening instrument. The methodology combines a multi-layer validation, yielding a structured taxonomy of 68 EETs across seven clusters, applied comparatively to Inland Waterway Transport (IWT), Short Sea Shipping (SSS), and Oceangoing (OG) fleets across retrofit and new built lifecycles. The framework is aligned with the European Green Deal, Fit for 55, EU ETS, FuelEU Maritime, and IMO mechanisms (EEDI, EEXI, CII), operationalized through 32 key performance indicators and a size-dependent policy indicator defining a feasible performance corridor. Three findings emerge: (i) coordinated deployment of operational optimization, hydrodynamic efficiency, and power conversion clusters delivers the greatest near-term emissions reductions, though without guaranteed long-term decarbonization impact, (ii) regulatory technological alignment is more advanced in IWT and SSS, while OG vessels face elevated uncertainty from fragmented global frameworks, and (iii) operational optimization and hydrodynamic measures offer the most immediate policy investment returns, whereas electrification is segment-dependent and renewable fuel solutions remain costly with limited near-term scalability. The framework provides a transparent, scalable basis for maritime energy planning, policy calibration, and investment prioritization across fleet segment.