The performance of Salters Duck as an energy extractor from ocean waves is studied. numerically on the basis of linear theory of surface waves and floating bodies, and experimentally by making use of hydraulic power transmitting devices. Quantities of engineering interest such as hydrodynamic forces, induced motions, efficiencies for extracting energy from ocen waves, transmitted waves and drifting forces are presented and discussed for fixed and for rolling only. The authors showed that the linear theory would be held for extracting energy from ocean waves as the first approximations.