The goal of FIT-HORIZONS is to reduce greenhouse gas emissions from the existing waterborne fleet by enabling ship owners and designers to evaluate combinations of retrofit technologies holistically, rather than assessing each technology in isolation. The project aims to deliver a validated tool environment reaching TRL 7-8 by the end of the project in 2029, together with six optimised retrofit designs – one per ship type – developed in virtual demonstrations where ship designers collaborate with ship owners and which are ready to be adopted on board after the project ends. For inland waterway transport, the goal is to demonstrate that hydrodynamic optimisation – aft-ship hull modification, adequate choice of propulsor type, number and positioning, and energy-saving devices – can substantially reduce the power requirements and emissions of inland vessels operating in shallow, restricted fairways. DST validates the predictive models through baseline and retrofit model tests in its shallow water basin, applies its FLUVIAL simulator to assess long-term voyage performance in realistic operating conditions, and leads the inland retrofit design study for the Haeger & Schmidt vessel MS Schwelgern, resulting in an investment-ready retrofit plan for a Rhine dry cargo vessel