The aim of this research was to investigate the possibility of a combined heat & power (CHP) plant, using the waste heat from a Suezmax-size oil tanker’s main engine, to meet all heating and electricity requirements during navigation. After considering various configurations, a standard propulsion engine operating at maximum efficiency, combined with a supercritical Organic Rankine cycle (ORC) system, was selected to supply the auxiliary power, using R245fa or R123 as the working fluid. The system analysis showed that such a plant can meet all heat and electrical power requirements at full load, with the need to burn only a small amount of supplementary fuel in a heat recovery steam generator (HRSG) when the main engine operates at part load. Therefore, it is possible to increase the overall thermal efficiency of the ship’s power plant by more than 5% when the main engine operates at 65% or more of its specified maximum continuous rating (SMCR).

The application of newly available technologies in the green maritime sector is difficult due to conflicting requirements and the inter-relation of different ecological, technological and economical parameters. The governments incentivize radical reductions in harmful emissions as an overall priority. If the politics do not change, the continuous implementation of stricter government regulations for reducing emissions will eventually result in the mandatory use of, what we currently consider, alternative fuels. Immediate application of radically different strategies would significantly increase the economic costs of maritime transport, thus jeopardizing its greatest benefit: the transport of massive quantities of freight at the lowest cost. Increased maritime transport costs would immediately disrupt the global economy, as seen recently during the COVID-19 pandemic. For this reason, the industry has shifted towards a gradual decrease in emissions through the implementation of “better” transitional solutions until alternative fuels eventually become low-cost fuels. Since this topic is very broad and interdisciplinary, our systematic overview gives insight into the state-of-the-art available technologies in green maritime transport with a focus on the following subjects: (i) alternative fuels; (ii) hybrid propulsion systems and hydrogen technologies; (iii) the benefits of digitalization in the maritime sector aimed at increasing vessel efficiency; (iv) hull drag reduction technologies; and (v) carbon capture technologies. This paper outlines the challenges, advantages and disadvantages of their implementation. The results of this analysis elucidate the current technologies’ readiness levels and their expected development over the coming years.