Abstract The ISWEC, Inertial Sea Wave Energy Converter, is an offshore, single body,floating wave energy converter. The ISWEC research group so far has designed and developed a device of which the floater consists of a monolithic steel hull with a semi-elliptical side profile, but rectangular from the up view. The actual ISWEC device is directional: for its correct functioning the hull is required to self allign in the wave direction. The objective now is the design of an omnidirectional device capable to absorb energy from wave coming from all the directions. This configuration have been considered optimal for the advantages introduced in terms of the WEC installation (no mooring system ) and release time as well as obtaining, at the same time, an increase in safety.