INDECS aims to reduce the fuel consumption and the greenhouse gas emissions on cruise ships. This is done by design improvements on the HVAC (Heating, Ventilation and Air Conditioning) system, in combination with optimal operation of all hotel functionalities, propulsion and the engines. Significant improvements can be done by considering each part separately, and further improvements are possible by taking a holistic view on the problem, as the different parts are not independent. INDECS will also provide a simulation-based test bench for engines of different sizes and types, which can speed up the introduction of new engine types with very low GHG emissions to cruise ships.