Third IMO Greenhouse Gas Study 2014

264 Third IMO GHG Study 2014
Regarding passenger ships, productivity is kept constant.
Remarks/caveats
If, given the projected productivity, the expected transport demand could be met by a smaller fleet, the active
fleet is not assumed to be reduced in the model, but the cargo load factor of the ships is assumed to decrease;
i.e. ships become less productive. If ships are scrapped/laid up or slow down instead, projected emissions
constitute an overestimation.
The historical ship productivity that serves as a basis for the projection of the future productivity development
of the ships is based on data that has a different scope: the tonnage data provided to us by UNCTAD is given
in terms of total tonnage, so does not differentiate between international and domestic shipping, whereas
the tonne-miles data is related to international shipping only. Using this productivity metric to project the
development of ships used for international shipping, we thus implicitly assume that the share of tonnage used
for international shipping and domestic shipping does not change in the future.
Ship size projections
In the emissions projection model, the ship types are divided into the same ship size classes as in the
emissions inventory model. For the emissions projection, the future number of ships per size category has to
be determined.
The distribution of the ships over their size categories can be expected to change over time according to the
number of the ships that are scrapped and that enter the fleet as well as their respective size.
The age of a ship and its cost efficiency determine when a ship is to be scrapped. In the emissions projection
model, a uniform lifetime of 25 years for all ships is assumed.
The size of the ships that enter the market is determined by several factors:
• the overall demand for the type of cargo transported by the ship type;
• the trade patterns regarding these cargoes, which depend on the geographical location of the supplying
and demanding countries/regions;
• the cargo load factors on the specific trades that can be expected depending on the potential size
of the ship; these load factors are not only determined by the total scope of the trade but also by the
frequency of the deliveries expected by the demanding party;
• the physical restrictions that a ship faces in terms of the dimensions of canals, waterways and the extra
costs of a detour (which could be lower than the cost saving when employing a larger ship);
• the physical restrictions a ship may face in terms of the dimensions (e.g. depth) of the ports and the
equipment of the terminals;
• the productivity of the ports/terminals, which has an impact on the amount of time that a ship is
non-active.
In the emissions projection model, it is assumed that, per size category, the average size of the ships will not
change, whereas the number of ships per size bin will change compared to 2012. The total capacity per ship
type, given a certain productivity level (in tonne-miles per dwt), is therefore assumed to be sufficient to meet
the projected transport demand.
Depending on data availability, two alternative approaches to derive the future number of ships per size
category have been applied (see Figure 41 for an illustration):
1 The total expected tonnage capacity of a ship type is first distributed over the ship size categories, and
then, by means of the expected average ship size per category, the number of ships per category is
derived; or
2 The total number of expected ships of a ship type is derived by first applying the expected average ship
size of all ships of the type to the total expected tonnage capacity of that ship type, and subsequently
the expected distribution of ships over the size categories in terms of numbers is applied.