Marine energy represents a very promising source of energy available worldwide. Although this energy is available in several forms, wave energy is the more widespread source characterized by high power density. In order to exploit energy from waves, numerous systems have been designed and commercialized. The Inertial Sea Wave Energy Converter is a device based on a floating body slack-moored to the seabed, using a gyroscope as a reference frame to produce electric power. This paper describes the design of the proposed converter equipped with two linear tubular permanent-magnet generators, exploiting the reciprocating motion between the gyroscopic system and the hull to generate power. The design of a two-phase linear tubular generator is analyzed. Experimental tests on a scale prototype have been performed.