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12 Third IMO GHG Study 2014
Figure 7: Time series for trends in emissions and drivers of emissions in the container ship fleet 2007–2012.
All trends are indexed to their values in 2007
Figure 8: Time series for trends in emissions and drivers of emissions in the bulk carrier fleet 2007–2012.
All trends are indexed to their values in 2007
Note: Further data on historical trends and relationship between transport supply and demand can be found in the Second
IMO GHG Study 2009.
The bottom-up method constructs the calculations of ship type and size totals from calculations for the fuel
consumption of each individual in-service ship in the fleet. The method allows quantification of both the
variability within a fleet and the influence of slow steaming. Across all ship types and sizes, the average ratio of
operating speed to design speed was 0.85 in 2007 and 0.75 in 2012. In relative terms, ships have slowed down
in line with the reported widespread adoption of slow steaming, which began after the financial crisis. The
consequence of this observed slow steaming is a reduction in daily fuel consumption of approximately 27%,
expressed as an average across all ship types and sizes. However, that average value belies the significant
operational changes that have occurred in certain ship type and size categories. Table 4 describes, for three of
the ship types studied, the ratio between slow steaming percentage (average at-sea operating speed expressed
as a percentage of design speed), the average at-sea main engine load factor (a percentage of the total installed
power produced by the main engine) and the average at-sea main engine daily fuel consumption. Many of the