Lately, acoustic data transfer has become an important topic in underwater environments. Several acoustic communication signals e.g. spread spectrum or frequency shift keying signals have been extensively developed. However, in challenging environments, it is still difficult to obtain robust acoustic links exceeding a data rate of 1 kbit/s. Binary Phase Shift Keying (BPSK) signals are a promising candidate to higher data rate communications. Within the European Fifth framework project ACME, a BPSK signal with an effective data rate exceeding 3 kbit/s was tested in shallow water environments. The differentially encoded signals were transmitted with a commercial modem over ranges up to 5000 m, in various topological configurations. It was observed that multipath and SNR strongly affect the quality of the received signal. These effects were partly overcome in the processing chain by including frequency correction and optimised equalisation techniques, thus, leading to very encouraging results.