Underwater acoustical 3D imaging is popular for underwater investigations due to its ability to give all the geometric information of the target. The computational complexity of the conventional time domain delay and sum beamforming (DAS) is a bottle neck for the real-time implementation of the acoustical 3D imaging. Many fast-beamforming techniques in frequency domain such as Chirp Zeta Transform beamforming (CZT) have been proposed to solve this problem. However, wideband pulse transmission for high resolution imaging makes frequency domain methods infeasible for the 3D acoustical imaging. In this work, we attempted to implement time domain delay and sum beamforming using software interpolation and compare it with the CZT beamforming. The simulation results show that software implementation of digital delay and sum beamforming is faster than CZT beamforming.