In this paper, a multiple-input hybrid frequency-time domain decision feedback equalizer is proposed to deal with the intersymbol interference in underwater acoustic communications. To track the time-varying underwater acoustic channel, a block-based adaptive algorithm is considered. In addition, we apply the overlap-and-save technique at the receiver. This technique makes it possible to remove the overhead due to the transmission of cyclic prefix over each block of data, such as in usual frequency-domain equalization systems. The second advantage of The OS technique is the possibility to change the block and equalizer sizes. The transmission scheme is validated in the Atlantic Ocean over a distance up to 2 kilometers in shallow water with high data rate single carrier QPSK communications (10 kbps). The receiver includes an efficient timing recovery tracking scheme followed by equalization. The results of simulations and experiments are evaluated in terms of bit error rate (BER) and mean square error (MSE).