Sustainability-Oriented Techno-Economic Assessment of Sulphur Compliance Strategies for an Aging Cruise Vessel Under SOx and GHG Constraints

Maritime transport remains a significant source of air pollution and greenhouse gas emissions, while existing vessels face increasing pressure to comply with both local pollutant limits and emerging carbon intensity constraints. This study presents a sustainability-oriented techno-economic assessment of alternative sulphur compliance strategies using real operational data from a 1998-built cruise vessel. Three scenarios were evaluated: a counterfactual heavy fuel oil baseline, heavy fuel oil operation with open-loop scrubbers, and full switching to marine diesel oil. Pollutant emissions were estimated using a Tier 3-oriented approach, while fuel-related Tank-to-Wake greenhouse gas intensity, prospective carbon cost exposure, total cost, break-even fuel price spread and sensitivity analyses were integrated into a decision support framework. Results show that scrubbers reduce SOx emissions by 96.9%, but increase fuel consumption, CO2 emissions and NOx emissions by approximately 3.6%. Marine diesel oil switching reduces SOx by more than 99%, particulate matter by 88.8% and CO2 by 4.6%, while also lowering prospective carbon cost exposure. However, under base case fuel price assumptions, heavy fuel oil operation with scrubbers remains the lower cost strategy, with a 2035 cost advantage of 4.03 to 5.30 million USD/year, depending on the carbon cost scenario. The findings show that the contribution of sulphur compliance strategies to sustainable maritime operation depends strongly on fuel price spreads, carbon cost exposure and remaining vessel lifetime under evolving regulatory conditions. By quantifying the trade-offs between local air pollution reduction, fuel-related carbon exposure and economic viability, this study contributes to sustainable maritime decision-making for aging vessels and supports compliance planning under regulatory uncertainty.