This paper presents the design concept of a hinged-type wave energy converter, Sea Wave Energy Extraction Device (SeaWEED), and associated numerical and experimental studies of its performance in regular waves. The device is considered as an improved attenuator. A SeaWEED unit consists of four modules that are connected by rigid truss structures. The four-module array includes a non-energy producing nose module in the front, followed by two energy producing modules, and another non-energy producing module at the rear. A potential-flow-based time-domain program with the Lagrange multiplier approach was developed to simulate the dynamics of multiple constrained bodies. Model tests of a 1:35 scale model with and without the power take-off (PTO) units were carried out to validate the numerical method. Friction dampers were designed and manufactured to mimic the PTO units. The validated time-domain method was applied to predict the absorbed power by the device in regular waves.