Rotors and bubbles: Route-based assessment of innovative technologies to reduce ship fuel consumption and emissions

This paper examines the potential of two innovative technologies—wind-assist and hull air lubrication—to help reduce emissions from new and existing ships. The authors conduct a route-based analysis of fuel and emissions savings by integrating global ship traffic data with weather data for eight commercial ships, five that use rotor sails (a kind of wind-assist technology) and three that use hull air lubrication. They place the results of that analysis in the context of the goals of the International Maritime Organization’s (IMO’s) initial greenhouse gas (GHG) strategy.

In all cases, rotor sails reduced route-level fuel consumption, CO2 emissions, and carbon intensity; savings ranged between approximately 1% and 47% (about 1% to 12% per rotor), and the magnitude depended on the type of ship, route, and associated weather conditions. Hull air lubrication yielded savings of between 3% and 13%; the potential for fuel savings and emissions reduction depends mainly on draught and ship speed. Hull air lubrication performance is less sensitive to geography and provides more consistent fuel savings.

The IMO’s initial GHG strategy, in addition to its longer-term vision of eliminating GHGs from the sector, calls for at least a 40% reduction in carbon intensity, as an average across the international fleet, by 2030 compared to 2008 levels. This requires significantly improving the fuel efficiency of the existing fleet. Given the retrofit potential of rotor sails in particular, and that ship lifetimes are typically 20 to 30 years or more, installing these technologies today could help reduce emissions and fuel costs now and for decades to come.

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