Techno-economic investigation of alternative propulsion systems for tugboats

In this paper, the main alternative propulsion systems based on internal combustion engines and batteries of a tugboat operating in harbour duties of the tugboat that include Emission Control areas are comparatively assessed. A hybrid propulsion system and two gas systems that one is with gas engines, other with dual-fuel engines are compared with a diesel system. For all cases, the harbour tugboats are investigated with 3 similar tugboat operation profiles. The gas and dual-fuel engines are assumed to operate using Liquefied Natural Gas and a small amount of diesel as pilot fuel, whereas diesel was regarded as the fuel for the case of the diesel engine propulsion systems. In the case of diesel-electric hybrid propulsion systems, the installation of hybrid components is also taken into account for reducing emissions and fuel consumptions. The propulsion systems are modelled and the techno-economical results were analysed in order to compare these systems. These results have been obtained by Life Cycle Cost that mainly consists of two main expenditures; Capital and Operational expenditures. Finally, these four alternative systems have been compared according to the calculated propulsion system costs for the 20-years operating period within the accepted assumptions and constraints.