Can conventional energy-saving technologies keep ships operating in European waters compliant with maritime climate regulations? A simulation-based assessment

Maritime transport is subject to increasingly strict emission regulation. Ships operating in European waters must comply with the International Maritime Organization’s Carbon Intensity Indicator, the European Union Emissions Trading System, and the FuelEU Maritime regulation, raising regulatory and financial pressure on the existing fleet. To stay compliant, shipowners can adopt conventional energy-saving technologies, such as hull and propeller upgrades. They offer an attractive short-term option, because they can be retrofitted to existing ships without switching fuels. How far such measures can keep individual ships within the tightening limits, and what they achieve across the fleet, remain unclear. To answer this, a model combining bottom-up emission estimation, regulatory compliance assessment, and techno-economic optimization is developed and applied to 12,908 vessels operating in European waters, projecting their outcomes from 2025 to 2030. Without technical or operational change, more than half of the fleet would become non-compliant under the Carbon Intensity Indicator by 2030. Under central assumptions on measure effectiveness and cost, conventional retrofits restore compliance for 27.6% of the affected vessels, rising to just under half in an optimistic case. This succeeds for most containerships, only rarely for cruise and passenger ships, and never for small tankers. Where feasible, the investment pays off within a few years, so cost is rarely the obstacle. For most ships, however, the reduction from these measures is too small to close the widening gap to the emission targets. Meeting them will therefore require options beyond conventional efficiency, such as advanced technologies or alternative fuels.