Cargo transport by sea and road - Technical and economic environmental factors

This paper presents the background for a method of calculating the energy demand for different ship types using only a relatively few, but important parameters. It is an empirical method, based on a statistical analysis of the main parameters of different ship types in order to establish representative relationships between the cargo capacity and the ship's main dimensions. On this basis, it has been possible to calculate the necessary propulsive power by using well-established empirical power prediction methods (Guldhammer & Harvald 1974, Oossanen 1980, Insel & Molland 1992). By combining the statistical analysis with a subsequent power prediction, it has been possible to develop a method which can calculate the energy consumption as a function of only three general parameters, namely the size of the ship (more precisely the capacity), the ship's speed and the average cargo utilization. Having established a method for the calculation of the ship's energy demand, it is relatively simple to calculate the exhaust emissions by using some well-established specific emission factors, i.e., figures for the exhaust emission per consumed energy unit (g/MJ). In the paper, a comparison with road transport is also presented, focusing on the energy demand and exhaust emissions per transport unit, i.e., per ton cargo per km. Finally, the energy and emission data are used for an economical evaluation of sea transport versus land transport. This is done by calculating the external costs to society caused by the negative effect of the different modes of transportation, i.e., costs due to air pollution, noise, accidents and congestion, which in total cover most of the external transport costs.