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Inventories of CO2 emissions from international shipping 2007–2012 71
• subdividing common vessel types into bin sizes based on deadweight tonnage or various capacity
parameters;
• providing vessel technical details, such as installed main engine power, maximum sea trial speed and
other parameters used in estimating vessel emissions;
• determining each vessel’s operational status by quarter for each year inventoried.
The IHS data were treated as accurate; however, this accuracy assumption introduces uncertainties if the
data fields used are inaccurate or unrepresentative. Potential uncertainties with the vessel characteristics data
include:
• data quality – does the field consistently represent the actual ship’s parameter?
• data source accuracy – is the field measured/recorded/verified on board the ship directly and is the
field accurate?
• update frequency – is the field updated at least quarterly (when a change has occurred)?
Data fields that have been independently spot-checked by consortium members indicate that the vessel class
fields (Statcode3 and Statcode5), main engine installed power, maximum sea trial speed and deadweight
tonnage appear to be generally representative of actual vessel conditions. The ship status field, which is
used to identify whether the ship is in service, is shown consistently to include more ships than are observed
in AIS (see Section 1.4 for details), for all ship size and type categories. There are two explanations for this
observation: either that the AIS coverage is not capturing all in-service ships, or that the IHSF database is
incomplete in its coverage of the number of active ships.
Another uncertainty associated with the vessel characteristics database concerns blanks and zeros in fields
that should not be blank or contain zero (i.e. length, deadweight, speed, etc.). To fill blanks or zeros, valid
entries were averaged on a field-by-field basis for each vessel type and bin size. These averages were used
to fill blanks and zeros (as appropriate) within the same vessel type and bin size to allow emission estimates
to be completed. The fields in which gap filling was used included main engine installed power, deadweight
tonnage, length, draught maximum, maximum sea trial speed, RPM and gross tonnage. This assumes that the
average of each vessel type and bin size is representative of vessels with a blank or zero and that the blanks
and zeros are evenly distributed across the bin.
In addition to the uncertainties listed here, there is uncertainty about the auxiliary engine and boiler loads by
vessel class and mode. As stated previously in Section 1.2.5 and Annex 1, there are no definitive data sets that
include loads by vessel class and operational mode for auxiliary engines and boilers. This study incorporates
observed vessel data collected by Starcrest as part of VBP programmes in North America (Starcrest, 2013) and
vessel auxiliary engine data collected by the Finnish Meteorological Institute for use in its modelling to build
upon the Second IMO GHG Study 2009 findings in this topic area. This improvement injects real observed
data and additional technical details but still relies on significant assumptions. Owing to the nature of the
sources profiled, the wide array of vessel configurations and operational characteristics, this area of the global
vessel emissions inventory will remain an area of significant assumption for the foreseeable future.
Relating to auxiliary engine and boiler loads, by mode, the following uncertainties that are inherent in AIS and
satellite data have a direct impact on the emissions estimated. For example:
• Vessels moving at less than 1 knot, for a certain period of time, are assumed to be at berth. This
assumption has implications for the oil tanker vessel class in which tankers at berth and not moving
faster than 1 knot will have auxiliary loads associated with discharging cargoes, which are significantly
higher than a vessel at anchorage.
• Vessels moving at less than 3 knots are assumed to be at anchorage. This assumption will cover vessels
that are manoeuvring and that will typically have a higher auxiliary load than those at anchorage.
However, tankers at offshore discharge buoys would not be assigned at-berth discharging loads for
the auxiliary boilers.
Finally, EF and SFOC remain areas of uncertainty. Emissions testing is typically limited for vessels and when
the various engine types, vessel propulsion and auxiliary engine system configurations and diverse operational
conditions are considered, emissions tests do not cover all the combinations. Testing that has been conducted
to date relies on previously agreed duty cycles, like the E3 duty cycle for direct-drive propulsion engines.
With the advent of slow steaming, is the E3 duty cycle still relevant? There are very few tests that evaluate