The numerical simulation of a hydro-elastic model involves the coupling between the hydrodynamics and the structural dynamics. The most common approach uses the Boundary Element Method to solve the hydrodynamics with a 3d potential flow coupled with the Finite Element Method (FEM) to solve the structural dynamics. One of the most recent works have proposed a full 3d time-domain hydro-elastic model using FEM-FEM to simulate tightly coupled problems (Servan-Camas et al. 2021)1. Solving the 3d hydro-elastic model is complex and requires a large computational cost. Reduced Order Models (ROMs) are mathematical simplifications of the physical high-fidelity models. They reduce considera-bly the time of the simulations allowing us to perform near real-time analysis. In this work, the methodology for solving the full 3d reduced order hydro-elastic model is presented. The structural ROM is based on the modal matrix reduction technique. The structural motion equations are projected onto the orthogonal truncated base composed of the eigenvectors. The displacement field is reconstructed as a linear combination of the modal amplitudes and the eigenvectors. In order to in-clude the hydrodynamic pressure loads, the structural ROM is integrated in the time-domain potential flow seakeeping solver SeaFEM2. The use of a structural ROM speeds considerably up the hydro-elastic calculations. This work has been developed under the H2020 project FIBREGY aimed to enable the extensive use of the fibre-reinforced composite materials in the structure of the next generation of large offshore wind turbine and tidal power platforms.