The extent of shipping decarbonization and reduction of air pollutant emissions remains limited, despite the rapid development of greening technologies. This is particularly valid for existing inland vessels and coastal ships. A large scale retrofit of the fleet would accelerate the greening transformation. However, there is a wide variety of ship types with different power demands and different required volume of energy carriers. Alternative fuels require more space on board and/or more frequent bunkering. The bunkering infrastructure for such fuels is scarce, and their future price levels are uncertain. Most measures are associated with considerable investments. In addition, the existing regulatory framework still does not provide an adequate support. The question arises: which retrofit solution would be the most adequate for a ship of certain dimensions, type, and operational profile? To answer this question, the project SYNERGETICS (Synergies for Green Transformation of Inland and Coastal Shipping) will: - create synergies between the leading research institutions in ship hydrodynamics and energy transition, innovation centres and shipbuilding industry, regulatory bodies, ship owners, and technology providers with the goal to provide a catalogue of retrofit solutions which will accelerate the green transformation of inland vessels and coastal ships. - demonstrate the greening capacities of retrofit by implementing hydrogen and methanol combustion in internal combustion engines on selected existing ships in real life operational conditions; - address the greening potential of hydrodynamics improvements, by demonstrating the effectiveness of the aft-ship replacement which comprises the optimized shape of the aft part of the hull, duct, propeller, and rudder design, and implementation of exhaust gas after-treatment and hybrid propulsion systems; - contribute to electrification of fleets by further developing swappable battery container services and a system for power management of ships with hybrid propulsion.