Impact of wind-assistance on the efficiency of a tramp fleet

Wind assisted ship propulsion (WASP) is expected to be an important element for the decarbonization of the shipping industry. However, studying WASP for a single vessel may neglect the full potential compared to planning a whole fleet of vessels as a unity. This lack of integration constitutes a substantial methodological and practical gap, given the strong inter-dependencies between wind propulsion performance, route selection, and economic–environmental trade-offs at the fleet level. We therefore extend a rich model for Tramp Ship Routing and Scheduling Problem (TSRSP) with weather-dependent routing to study the synergies. The TSRSP model includes speed optimization, bunkering, charter costs, and spot market, hence making it possible to optimize the full set of operational decisions to get the largest benefits of WASP. Historical freight rates and bunker prices supplied by a collaborating shipping company are used in the experiments, covering 9 to 20 vessels, operating in 35 predefined regions. When profit only is maximized, the results show that 5% higher profits and 8% lower emission can be obtained using WASP compared to the business-as-usual scenario. Moreover, using a multi-criteria setting, it is seen that at least 30–40% reductions in emissions can be reached while maintaining the same overall profit. Finally, we assess the impact of optimizing the entire fleet simultaneously compared to considering each vessel individually, showing that the fleet-oriented approach can achieve twice the emission reduction achieved by the vessel-oriented approach. These results show that WASP is an important measure for reaching IMO’s emission goals.