We present here the experimental determination of the dispersion relation of surface waves of a ferrofluid submitted to a steady vertical magnetic field. The results are compared to a linear theory where all the magnetic characteristics of the fluid have been taken into account. The knowledge of the dispersion equation is then used to analyse the capillary-wave resistance, that is the drag force associated to the emission of waves by a moving disturbance at a free fluid surface. It undergoes a transition from zero to a finite value as the speed of the disturbance reaches a certain critical value. The effect of viscosity is explored, and a magnetic fluid is shown to allow controlling the critical speeds. Contrary to the theoretical model, however, the measured wave resistance reveals a non monotonic speed dependence after the threshold.
