A new concept of energy HUB in the Mediterranean Sea has been recently proposed by National Research Council of Italy. It consists in an energetic archipelago where various devices for exploiting marine renewable energy can coexist in a modular way. This archipelago is surrounded by floating breakwaters which ensure the creation of a protected sea area, where new kind of blue energy converters can be installed. The possibility to implement a dual use of these floating breakwaters, as offshore dam and wave energy converter, represents an interesting challenge. In extreme and severe sea-states, it should strictly work as a passive breakwater, absorbing the incoming waves and protecting the devices installed in the archipelago. Otherwise, in more frequent mild sea states, the floating breakwater should behave as WEC, contributing to the energy production of the archipelago. The dual functionality is achieved through a different draft, that directly dependent on the amount of water pumped in the module, increases the displacement of the floater. In the breakwater functionality, the module is almost fully submerged, providing a large stability of the device and a large reflection and dissipation of the incoming waves. In contrast, when the module behaves as WEC, a lower displacement is required, enabling larger device motions. In this study, through the linear potential flow theory, the feasibility of this innovative double functioning device is investigated, focusing on heave and roll behaviours. Results allow the identification of the optimal draft configurations able to satisfy the two different functionalities.