To improve the accuracy of model tests, fluid dynamical problems of circulating water channel are considered by surveying the free surface inclination. Fundamental characteristics of the free surface inclination are studied by systematically controlling the water volume and the setting angle of the plate of the wave suppressor. From the practical viewpoint, the evidence is shown that the effects on the free surface inclination is unchangeable regardless of changing the water volume and the plate angle. A practical correction method is proposed that of diminishing the influence of the steady wave and the free surface inclination from results of measured resistance by traversing model to longitudinal direction. The reasonability and reproducibility about the conventional driving method is investigated, that of keeping the minimum condition on the steady wave height by adjusting the water volume and the plate angle.
