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174 Third IMO GHG Study 2014
experienced over the period of operation. While it is theoretically possible to match the routing data in AIS
with historical meteorological data to produce an estimate of weather impacts experienced on a ship-byship,
voyage-by-voyage basis, the level of detail for input to the calculation and the computational resources
required to apply this to the world fleet over the course of a year is not feasible within this project.
Consequently, the approach taken here is to apply findings from other more detailed studies. Work by Prpić-
Oršić and Faltinsen (2012) undertook a detailed modelling of the effect of weather on fuel consumption
for an S-175 container ship in the North Atlantic using state-of-the-art models for ship added resistance.
Their calculations revealed that this ship type had, on average over the voyages, a 15% increment in fuel
consumption over the calm water fuel consumption.
Whilst simplistic, this same assumption is applied as a starting assumption for the average increase in resistance
for all oceangoing ship types (as classified according to the Second IMO GHG Study 2009) in this study. A
lower value of 10% is applied as the added resistance of coastal shipping, as it is expected that they would
experience, on average, less extreme environmental conditions.
Activity and fleet data merger
The activity and ship technical data merger is conducted using scripts that match the activity file’s IMO or
MMSI numbers with the corresponding ship in the appropriate annual IHSF file. Due to constraints imposed
by the consortium members’ pre-existing licensing agreements for both activity and ship technical data, during
the merger process the ship identification fields (IMO and MMSI numbers) are removed to make the merged
file anonymous at the ship level. A unique reference number is generated for each observed ship along with a
merged activity and ship technical data file structure for each year. If a ship is observed in the activity data but
not matched to the IHSF data set, the ship’s activity data is returned unchanged. The ship status field is utilized
for both observed and unobserved ships in the cargo-carrying ship type. The process is illustrated in Figure 9.