Slow steaming is the practice of reducing maritime vessel speeds. By operating ships at a speed significantly lower than their maximum speed, the required fuel is reduced. This results in reduced CO2 emissions. Different ship types benefit differently from slow steaming. There can be implications for frequency of services which should be considered in terms of available capacity and potential need for additional ships.
As there is an exponential relationship between speed, engine power and fuel oil consumption. Slow steaming can reduce the amount of fuel required to operate a ship more than proportionately, resulting in equivalent reduced emissions. Longer trip durations however, mean longer journey times.
This can yield significantly reduced CO2 emissions although. A study found a speed reduction of 10% translates into 27% reduction in engine power requirements and in a 19% reduction in overall engine power to cover the same distance (as more time is needed to cover it). Lower speeds are more effective if design speeds of ships are brought down as well. The only potential adverse effect may result from the increase travel time that will affect the transport cost of some commodities that may decide the change for faster transport alternatives (e.g. road and rail).
Speed reductions of up to 30-50% (depending on ship type) compared to design speeds can reduce CO2 emissions of up to 40%.
The implementation of lower speed limits for maritime vessels has no direct costs.
However, operating a lower speeds means increased travel times which would imply crew is paid for more days and frequency of service is reduced if no mitigating actions are taken.
Slow steaming can lead to a reduction in other pollutant emissions too.
Slow steaming may require ships to run their engines in sub-optimal conditions, which could create issues such reduction of engine efficiency and lifespan and potentially relatively higher emissions of NOx and particulate matters. Newer vehicles are designed to operate at lower speeds, effectively removing this problem.
Slow steaming increases voyage duration. As a result, goods take longer to reach their final destination, which could have an impact on costs and their value.
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