This document presents the metocean design basis of offshore test site �� SEM-REV �� operated by Centrale Nantes and dedicated to the test of floating wind turbines and wave energy converters. It is released in order to provide data for offshore operations and engineering in the French offshore area of South Brittany and Pays la Loire regions. It presents a metocean analysis, based on a Measure-Correlate-Predict approach in a consolidated report which provides simultaneously design data for wind, waves, current, tides and marine growth on a French site. In particular, it uses data issued from more than 10 years of continuous campaigns performed since the creation of SEM-REV test site since 2009: 2 years of wind measurements, 10 years of wave measurements and 19 ADCP campaigns for current measurement. The provided design data are operational statistics and long-term statistics such as values for return periods of 1, 5, 10, 25, 50 and 100 years and for various directional sectors. Additional information are also provided such as turbulence intensity, extreme direction change for wind. Scatter diagram, monthly distribution, beaking wave criteria��� are provided for waves. Harmonic analysis of tidal measurements enable to hindcast and forecast water elevation on site. Deeper analysis of current on the water column is also provided. Marine growth thickness is evaluated on various components such as chains, nylon and dynamic cable. Additionally, other environmental conditions such as air density, normal and extreme air and sea temperature ranges are presented. This report was appraised by Bureau Veritas Marine and Offshore which �� certifi[es] that the metocean condition of the SEM-REV Test Site has been appraised according to the following international standards : IEC 61400-1:2019 Wind turbines ��� Part1 : Design requirements IEC 61400-3-1:2019 Design requirements for fixed offshore wind turbines IEC 61400-3-2:2019 Design requirements for floating offshore wind turbines [...] The metocean design basis of SEM-REV test site presented, and the associated Measure-Correlate-Predict based method has been found in compliance with the above standards [���] ��