This thesis presents a comprehensive Decision Support System (DSS) for selecting greenhouse gas (GHG) emission reduction technologies for heavy-lift vessels (HLV) owned by Jumbo Maritime. Given the increasing regulatory pressure from the EU and IMO, shipping companies must evaluate cost-effective solutions. Using the Best-Worst Method (BWM), the DSS prioritizes alternatives based on financial viability, operational flexibility, and technological readiness. The study examines eight sustainable retrofitting technologies and their selection methodology. Sensitivity analyses and verification tests confirm the robustness of the DSS rankings. The research highlights the limitations, implementation strategies, and the broader implications of sustainable decision-making in the maritime sector.