The purpose of this paper is to present the communications aspect in Thetis, a real time multi-vehicles hybrid simulator for heterogeneous vehicles. This simulator allows hardware in loop (HIL) simulations including virtual sensors which allows to provide a representation of a virtual world, and with the support of communication devices, which allow overall communications between vehicles. After a short state of the art, we introduce the main mechanisms of our simulator. Then we present the modeling of the phenomena which are encountered when AUVs (Autonomous Underwater Vehicle) communicate with aquatic modems, and the messages distribution system considering the assumptions we have made. Finally, we present results of our Hardware In Loop Simulation in which Taipan 2 and Taipan 300 (our 2 AUVs) exchange messages in different spatial configurations.