Approximately 70% of Earth's surface is covered by a continuously moving body of water. Ocean waves are a vastly underutilized sustainable energy resource with an estimated annual power reserve of 3 TW. In this study, a floating rotating mass type wave energy converter is designed and built to harvest kinetic energy from omnidirectional, low to high frequency ocean waves without requiring a mooring system connecting it to the seabed. The wave energy converter comprises an oscillating weight inspired by automatic watches, interconnected with bidirectionally moving rotational triboelectric nanogenerators. The oscillating weight rotates similarly to an automatic watch's oscillating weight and its design is optimized by multibody dynamics simulation. Under a 2 Hz water wave and 5 GΩ matched resistance, a single 10 cm diameter device produces a peak power output of 200 μW and a power density of 304.4 mW m−3. Numerical and experimental work has been conducted to develop the wave energy converter, offering a new device architecture that is simple to build and scale up, paving the way for efficient harvesting of ocean energy.