A strong contender for the utilization of the hydropower sources is Savonius turbine because of its good starting characteristics and simplicity in fabrication. The aim of the present work is to study the effect of overlap ratio and aspect ratio on the performance of a Savonius turbine for hydrodynamic application. The findings would be useful to decide design parameters of a Savonius hydrokinetic turbine. This study is conducted in three open channels namely small laboratory channel with depth of water 270mm, large laboratory channel with depth of water 480mm and a real life irrigation canal with depth of water 900mm. Influence of endplates is studied to establish the significance of their presence on rotor performance. Maximum coefficient of power is observed for an overlap ratio of around 0.11 for Savonius turbines with aspect ratio less than 0.6. For a given overlap ratio, the increasing trend of the coefficient of power is observed with the increase in the aspect ratio. However, for aspect ratios greater than 1.8, the coefficient of power becomes nearly stagnant. Copyright (C) 2016 John Wiley & Sons, Ltd.