Comparative analysis between different methods for calculating on-board ship's emissions and energy consumption based on operational data

With the aim of more reliably measuring ships' fuel consumption and emissions several different estimation methods have been put forward and are in use but there is ongoing debate still on the best way to measure maritime emissions. Fuel and emissions monitoring are already a common practice in the shipping industry. But there are currently neither harmonised guidelines nor legal requirements that clearly define the method and the rules to follow to monitor on-board fuel consumption for each situation during navigation. In this context, this article describes and compares four existing methods (EPA, IMO, Jalkanen and MAN) for calculating energy consumption and emissions, and presents a more realistic method, based on a case study. The purpose is to examine the differences between all of these methods, in order to propose the most suitable method of obtaining the data needed for better energy management, and a method that can be applied to any type of ship. The case study was carried out on Ro-Pax ships, comparing these four different methods through the application of a bottom-up integrated system approach. The study describes in detail and applies the most complete methodology for calculating energy consumption and emissions during cruising, operating in a Speed Reduction Zone (SRZ), manoeuvring and berthing. Application of the new improved method proposed in this paper could be the first step in implementing operational measures for detecting both abnormal high emissions and abnormal fuel consumption. The application of this method does not, in itself, reduce fuel use or improve efficiency, but it should be the necessary first step to establish uniform operational measures that will improve the management of energy on board ship and monitor accurately the performance of the fleet.