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Methodology: LIPASTO unit emissions database

The following links help navigate the LIPASTO unit emission general description and mode-specific methodology descriptions.

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Waterborne transport

Introduction

Waterborne transport has long traditions, characterised by relatively slow technological progress and long life time of vessels. The recent years have nevertheless shown more rapid change direction that is likely to continue. Engine technologies and improved use efficiencies have had a major impact on fuel consumption and emissions. The emission factors published on LIPASTO pages are conservative, and if more detailed emission information of a specific vessel is available, that should be used for any emission calculation.

LIPASTO unit emissions for waterborne transport are shown per ship kilometre, per transport unit (such as container or car), per net tonne kilometre and passenger kilometre. These are typically the most suitable choices that also allow fair comparisons between vessels, vehicles or even transport modes. Other possible choices could be based on for example volume or freight lanes.

Unit emissions aim to take into account real loading factors (capacity usage) of two-way round trips. Therefore LIPASTO emission factors might be higher than those in other databases that assume more optimistic but theoretical loading factors (even 80%) that are rarely achievable, especially when taking into account return trips.

Definitions

  • Ship kilometre means transport over one kilometre by the ship.
  • TEU (Twenty-foot Equivalent Unit) means one container of 20 feet (1 TEU). Larger containers of 40 feet are also used (2 TEU). TEUs are a typical unit to announce capacity of a freight ship even though it is not fully accurate and comparable in usage of different ship companies.
  • Tonne kilometre [tkm] means one net tonne of freight transported over one kilometre. Tonne kilometres of a trip are calculated by multiplying the distance transported by the net weight of freight.
  • Passenger kilometre [pkm] is the transport of one passenger over one kilometre.
  • DWT (dead weight tonnage) means the total weight of freight, fuel, fresh water, ballast water, provisions, passengers and crew.
  • Net load (net tonnes) means effective weight of the load. Weight of a container is not included but any fixed packaging is. The weight of e.g. a container, which contributes to amount of energy consumed, has been acknowledged in the weight of the ship when computing unit emissions.
  • GT (Gross tonnage) means ship's overall internal volume.
  • Passenger from maximum capacity (loading factor) means average number of passenger per total passenger capacity of a ship.
  • Trailer is a common name for a transport unit on wheels, typically transported on a Roro ship.
  • Trailer kilometre [trailer km] is transport of one trailer over one kilometre on a ship.
  • Trailer capacity [pcs] means total trailer capacity of a ship.
  • Trailers from maximum capacity (loading factor) means average amount of trailer per total trailer capacity.

Speed

Speed has an important role in waterborne traffic. The equation below shows that fuel consumption of a ship changes relative to the change in the speed raised to the power of a. The equation is valid near design speed with the value of a = 3. For example, a 10 % increase in speed (from 20 to 22 knots) leads to a 33 % increase in fuel consumption. Similarly, a decrease in speed leads to a decrease in fuel consumption, which is actually the easiest and most effective way of reducing fuel consumption as well as emissions.

F = fuel consumption (t/day)
F* = fuel consumption at design speed
S* = design speed
S = actual speed
a = constant value of circa 3

Allocation

When a vehicle carries both passengers and freight, a decision on how to allocate energy consumption and emissions for these user groups has to be made. Allocation is hardly unambiguous with any transport mode, but waterborne traffic seems to be even trickier. A Swedish study found at least 19 different alternatives for allocation methods but none of them was judged significantly superior to the others.

For LIPASTO pages, the allocation method is based on space usage by passengers and freight. About 80 % of the deck-space in ferries is reserved to accommodate passengers and about 20 % is reserved for freight (MeriMIPS, in Finnish). Thus 80 % of the energy consumption and emissions in ferries are allocated to passengers and the remaining 20 % to freight. For Ropax vessels where the share of passengers is smaller, around 16 % is allocated to passengers.

Sources of information

Information from shipowners. Confidentially shared information from shipowners ensure that theoretically calculated figures correspond to real world situations. In practice this means that calculated energy consumption of vessel types was in line with observations from corresponding real ships. Suchlike measure to verify power usage (kWh) is especially important in Finland because of the heavy ice-strengthening on most ships. Ice-strengthening requires extra reserve power up to 30 % more compared to navigating on open waters. Internationally power usage out of nominal power is typically estimated at 80 %. This does not apply to Finland, as it has been shown that a smaller percentage of nominal power is actually used. Fuel usage has also been lowered by means of slower speeds and more efficient navigation. Information provided by shipowners and their willingness to cooperate in emission calculations shows that the industry is open for discussing real impacts of waterborne transport as well as actively seeking ways to improve.

Emission factors are mainly based on the MEERI calculation model developed by VTT. The model produces average figures for each vessel and ship type. Some emission information was also provided by shipowners. Shipowner data was especially important for ferries, where cleaning technologies and fuel types in use vary. Sulphur directive states that sulphur content is restricted to max. 0,1 %, which can be achieved by using a low-sulphur fuel oil (LSFO) or heavy fuel oil combined with exhaust gas scrubbing. In general, ship fuels are in transition, and it is difficult to describe this continuously evolving fuel scheme.

Port emissions are included in the emission factors. The amount of port emissions depends on ship type and route. For vessels travelling long routes the relative share of port emissions is smaller than for vessels on short routes.

Background data

Values used for computing unit emission factors are available in the background data table.