A pre-study focusing on the possibility to create a retrofit installation of a fuel cell propulsion system on-board a vessel. In the search for a clean sustainable fuel alternative for the maritime sector, hydrogen has gained a lot of interest during the latest years. One key advantage of hydrogen is that it can be produced in a sustainable manner trough renewable energy, and it doesn’t emit any greenhouse gases (GHG) when used. However, even if the interest from the industry is increasing and a number of pilot-projects are announced, several barriers to overcome still exist. Primarily the remainingissues are linked to safety regulatory aspects, in summary a need for more knowledge and practical experience of using hydrogen in marine applications. In this pre-study, the area of using hydrogen for fuel cells on-board a ship is further investigated. The overall object of this study is to contribute to a heightened knowledge regarding the use of hydrogen and in particular aspects related to safety and regulatory issues. The goal of this study was to start the development of a roadmap for a full-scaleinstallation of a hydrogen-powered fuel cell drivetrain in an existing ship (so-called retrofit installation). To achieve this, the study was built around Ventrafiken's passenger ferry Uraniborg, which operates between Landskrona and Ven in the south of Sweden. By analysing data from the ships power management system and conducting a hazard identification analysis, a potential fuel cell/battery concept was formulated. The result shows that it is possible through retrofit to install a fuel cell-based propulsion system in combination with batteries, which also are aligned with safety concerns. However, in the case of Uraniborg it would involve extensivealterations on-board, and several areas still exist where further studies are needed before taking on such an endeavour. In summary, the conclusion is that the suggested design is a conceivable concept that could be implemented. But in the case of Uraniborg it would be easier to build a new vessel adapted for hydrogen operation than to make a retrofit. This, due to the alterations that would be needed in the ships interior design in order to store and manage hydrogen in a safe way, for example to keep it separated from areas where personnel are present as well as spaces where electrical installations are present. In addition to the theoretical concept, the project has also created an industry network for hydrogen in maritime applications with a total of 47 industry members at the time of writing. The network will continue to support the implementation of hydrogen in maritime applications through knowledge sharing and support the creation of new research and development projects, even after the end of this study.