This paper describes a method that could generate electric energy from the propagating ocean waves by implementing an actively controlled tuned mass damper on a ship sailing on the ocean. There are three fundamental requirements for any alternative energy method to make it work in practice. The first issue is that there should be affluent energy sources in the nature. Then, we should collect and confine them in a compact space by means of a smart method. Finally, we must convert the renewable energy into electric power as fast as possible. The author discusses the weak points and strong points of the proposed power generating method, while paying attention to these three requirements. The author started an observation project that the vibration data from the vessels sailing on the ocean would be collected under different conditions. The motion data obtained from a ship on the ocean gives the energy density spectrum in the frequency domain, which verifies the first requirement mentioned above. There is the appropriate natural period that determines the performance of the device, or equivalently the power of the generator. The solution for the second requirement is the tuned mass damper method, which indirectly collect the energy from the primal system to the auxiliary system by means of gravity. The last requirement is satisfied by the unique control algorithm known as acceleration feedback method, which enhances the cost performance of the tuned mass damper with the low frequency dynamic property.