One of the greatest challenges of the 21st century is the reduction of greenhouse gas (GHG) emissions. The shipping industry accounts for 2.9% of global GHG emissions and faces increasing pressure to meet the climate goals set by the International Maritime Organization (IMO) and the European Union, as part of the broader global effort to limit temperature rise to 1.5°C under the Paris Agreement. Al- though the shift towards various forms of alternative fuels in the new-build market is clearly evident, 30% of the global fleet is expected to be non-compliant with the prevailing regulations within the next three years (2023-2026). Replacing all non-compliant vessels with new-builds within this timeframe is not feasible due to the limited capacity of the shipbuilding industry. This presents a critical challenge for the maritime sector, making retrofitting existing vessels a potential, and perhaps even necessary, solution.

Methanol, a cleaner alternative fuel, shows significant promise in reducing GHG emissions, especially when produced from renewable sources, such as Green-methanol or E-methanol. The initial signs of methanol adoption in new-building market appear to be successful, and the retrofitting of existing ships is seems to be feasible both in theory and practice. However, the conversion of an existing ship to methanol propulsion presents challenges, primarily due to the fuel’s lower energy density and its toxic- ity. These factors make the costs for methanol storage in the vessel and operational fuel consumption notably more dominant. Consequently, the potential cost savings from Energy-Saving Devices (ESDs), which can be installed during a vessel conversion, become more relevant.

The main objective of this thesis is to gain deeper insight into which retrofit strategies, in terms of methanol tank volume and the inclusion of ESDs, can provide a feasible option for retrofitting existing vessels to methanol, achieving the intermediate GHG reduction goals. A refit indicator model is devel- oped to evaluate various retrofit strategies, focusing on financial and regulatory performance, given a scenario of price trends and regulatory developments. The model incorporates key operational factors such as trip distance, sailing speed, and bunkering intervals. In a case study, a single base-case vessel was converted into several conversion cases, differing in methanol storage capacity and the inclusion of ESDs, and their performance was assessed under various potential future scenarios.

The results of this study suggest that significant reductions in GHG emissions can be achieved. Pro- vided that renewable methanol is used, it is possible for a methanol-converted vessel to meet the intermediate GHG reduction goals. The regulatory performance of many methanol vessel conversion strategies is also favorable, particularly when a methanol conversion is combined with one or more ESDs. The results showed that, in such cases, vessels can remain compliant for 15 to 20 years longer compared to their non-converted base-case. An important finding is that the shift from a tank-to-wake to a well-to-wake regulatory perspective is a key factor in the success of methanol retrofits. From a financial view, it can be concluded that the strategy of converting to a limited methanol tank volume, combined with a number of highly fuel-efficient ESDs, appears to be the most effective solution for the medium to long term.