In recent years, the development of CFD simulations has increased the knowledge in fluid-structure interaction problems. This trend has been particularly important for floating offshore wind turbines (FOWTs) and sailing boats. However, especially for these sectors, in which two different fluids are involved, the reliability of CFD prediction tools requires further experimental validations. To this end, as a complementary approach with respect to ocean wave basins, there is the need for wind tunnel aero-elastic dynamic tests. This paper presents the customization of a 6-degrees-of-freedom (DoF) motion-simulator device for hardware-in-the-loop (HIL) wind tunnel tests on floating scale models. Each step of the machine design-loop is motivated and described: the kinetostatic synthesis is obtained through a multi-objective optimization using a genetic algorithm, the inverse dynamic properties are mapped on the workspace, and finally the drive system is mechanically sized using the so called alpha-beta theory. The emphasis is placed on the mechatronic design methodology, so that different mechanisms and requirements may be considered. (C) 2014 Elsevier Ltd. All rights reserved.