The effects of slow steaming on the environmental performance in liner shipping

The environment issue is one of the significant challenges that the liner shipping industry has to face. The International Maritime Organization (IMO) has set a goal to reduce greenhouse gas (GHG) emissions from existing vessels by 20-50% by 2050 and develop the Energy Efficiency Operational Indicator (EEOI) as a measure for energy efficiency. To achieve this goal, IMO has suggested three basic approaches: the enlargement of vessel size, the reduction of voyage speed, and the application of new technologies. In recent times, liners have adopted slow steaming and decelerated the voyage speed to 15-18 knots on major routes. This is because slow steaming is helpful in reducing operating costs and GHG emissions. However, it also creates negative effects that influence the operating costs and the amount of GHG emissions at the same time.This study started with the basic question: Is it true that as voyage speed reduces, the operating costs and CO2 emissions can be reduced at the same time? If this is true, liners will definitely decelerate their voyage speed themselves as much as possible so that they can increase their profits and improve the level of environmental performance. However, if this is not true, then liners will concentrate just on increasing their profits by not considering environmental factors. This led the authors to set out three objectives: (1) to analyze the relationship between voyage speed and the amount of CO2 emissions and to estimate the changes by slow steaming in liner shipping; (2) to analyze the relationship between voyage speed and the operating costs on a loop; and (3) to find the optimal voyage speed as a solution to maximize the reduction of CO2 emissions at the lowest operating cost, thus satisfying the reduction target of IMO.