The number of cruise ships sailing is growing constantly worldwide, driven by a continuously increasing number of passengers. Higher attention to this ship segment runs together with more complex energy systems installed on board due to the needs of improving energy efficiency and reducing operational costs. For these reasons, ship Owners and Shipyards are involved in the design of power plants and energy management systems that ensure lower fuel consumption and compliance with increasingly stringent IMO regulatory requirements on emissions. To respond to these needs, we hereby introduce LESS (Low Energy Ship deSign tool), a simulation environment developed to support the designers to choose among different propulsion/hotel plants solutions since the early stage of the ship design. The software allows analyzing the energy performance of different plant layouts and system components and eases the integration of energy recovery solutions. In particular, the library of components includes heat recovery packages such as Organic Rankine Cycles (ORC) systems to reduce “non propulsive” power demand.