Previous studies showed the importance of three-dimensional effects when calculating the characteristics of a scaled downturbine rotor [1, 6, 7]. The results of 3D RANS computations of Make and Vaz  are taken to calculate 2D lift and dragcoefficients given as input to FAST (BEMT tool from NREL). With this BEMT tool the rotor characteristics (power and thrustcoefficients) are calculated. We term this the RANS-BEMT coupled approach. This approach is compared to measurementscarried out at MARIN and the direct 3D-RANS computation.