Speed Reduction as an Emissions Reduction Measure for Fast Ships

Ships that sail at high speeds emit a higher amount of air emissions on a per tonne-km basis than ships that goslower. As the goal of environment-friendly shipping is high on the agenda of the IMO, the European Commission and many individual coastal states, reduction of emissions, both from greenhouse gases (GHG)such as CO2 , and also from SOx, NOx , and other gases, is an important and urgent target. One of the obvious operational measures that is contemplated to reduce emissions is speed reduction. As there is a cube law between speed and fuel consumption per day, the higher a ship’s speed is, the more her emissions can be reduced byspeed reduction. This is particularly true for high speed craft but also for containerships, RoPax ferries and other ships that go faster than the average. However, a reduction in speed may have undesirable side-effects that may generally entail non-trivial costs. Such side-effects may include the need for more ships in the fleet, increased cargo inventory costs, and others, and collectively may render speed reduction not necessarily cost-effective. Alternatively, one may compensate by reducing port time, to the extent possible. This paper investigates such issues for a variety of ship types at the higher end of the speed spectrum and attempts to identify factors that are important and alternatives that are more cost-effective.