In order to investigate the propulsive performances of “Ro” that is oriental sweep used to propel a Japanese traditional wooden ship, the authors analyze geometrically the motion of “Ro” when rowing it first of all and make clear the principle of propulsion by “Ro” in the present paper. According to the results of such analysis of the motion of “Ro”, manufacturing of the rowing machine of “Ro” is discussed. The open tests have been carried out by rowing the model “Ro” of 1/3 scale installed on the realized rowing machine. Furthermore the self-propulsion tests of a 4 metres long model ship propelled by “Ro” operated by the rowing machine set-up in the model ship have been performed in the towing tank. As the results of such experiments the hydrodynamic characteristics of “Ro” have been made clear experimentally for the first time. For example, the efficiency of “Ro” is possible to be more than 0.70 in a good case but less than 0.40 in a bad case. In the worst case any thrust cannot be gained. Accordingly the propulsive performances of “Ro” strongly depends on the skill of a rower.