Third IMO Greenhouse Gas Study 2014

Annex 3 205
than 1 is 19, 34, 33 and 37 respectively. The differences observed in 2009 are attributable to the fact that there
is no satellite-derived activity data in this year.
Figure 19: Difference between average speed at sea for each ship size and type category.
Negative values indicate that LRIT data provides a lower estimate of speed
than the extrapolated AIS data
In summary, there is good confidence about the days at sea and speed estimates for 2010 to 2012, both
regarding a lack of bias and convergence in estimates of these variables when there is high confidence in the
AIS extrapolation. However, for 2009 and for low-confidence AIS extrapolation estimates (less than 40%), bias
is evident, tending to increase the days-at-sea percentage.
Fleet technical data quality
Evaluating the technical fields from 2007 to 2012 used for estimating ship emissions, the fields with over 99%
coverage over the study time frame include Statcode3, Statcode5, gt, propulsion type, number of screws and
date of build. The fields with the poorest coverage (under 50%) over the study time frame include length, main
engine (ME) fuel consumption and total fuel consumption. It should be noted that the IHSF database did not
include keel laid date until 2012. A qualitative field quality was initially assigned based on consortium members’
evaluation/use of fields in previous projects and input from IHS Maritime. The qualitative designations include
“representative” and “speculative”. “Representative” designates that, based on previous work with this field
on other projects, the field is generally found to be representative of the actual ship characteristic and reliably
reported across numerous ships. “Speculative” designates that, based on previous work with this field on other
projects, the field is generally found to be inconsistent with the actual ship characteristic and/or not reliably
reported across numerous ships. Again, at this time the quality designations are based on the past experience
and judgement of the consortium for a particular field, with input from IHS Maritime.
A comparison was conducted for the 2007 to 2012 observed cargo-carrying ships (identified with AIS and
S-AIS activity), which showed improvements in the coverage of several of the fields. Fields in which coverage
is improving are beam and RPM, while dwt, maximum draught, ship speed, and installed ME power had
similar coverage across the study time frame. The coverage of the cargo-carrying fleet with respect to the
various fields utilized for this study is presented in Table 13.