In this paper, the main alternative propulsion plants based on reciprocating internal combustion engines of a ferry or RoRo ship operating in routes that include Emission Control Areas (ECAs) are comparatively assessed. Specifically, a dual fuel engine propulsion plant is compared with a conventional Diesel engine plant. For both cases, the installation of a waste heat recovery system, which covers a part of the ship electric energy demand, is also considered. The ship main OF engines are assumed to operate using LNG and a small amount of MDO for initiating combustion, whereas low sulphur MOO was regarded as the fuel for the case of the Diesel engine plant. The installation of Selective Catalytic Reduction (SCR) after-treatment unit for reducing the NOx emissions for the case of Diesel engines plant is also taken into account. The propulsion plants were modelled under steady state conditions, and the simulation results were analysed in order to compare the alternative configurations. Furthermore, the Energy Efficiency Design Index (EEDI) values were calculated and the two examined propulsion system cases were compared on EEDI basis. Finally, the Life Cycle Cost for each alternative propulsion plant was calculated and used for completing an economic evaluation of the Dual fuel propulsion plant versus the conventional designs applied in ferries. (C) 2014 Elsevier Ltd. All rights reserved.