Abstract: The paper presents a multi-beam digital sonar that was designed for monitoring and fish stock assessment in in/and waters. The sonar can also be used as a bottom profiler in lakes, rivers and shallow sea areas. The hexagonal piezoelectric transducer array co-operates with a commutator set. The 32 -channel digital beamformer creates 30 narrow receiving beams in every 60^o sector of simultaneous observation. The six sectors cover the whole 360^o angle range of the sonar. The beamformer digital signal processing is based on second order sampling of echo signals and the phase-shifting principle of beam deflection. The sonar block diagram, beamformer algorithms, as well as transducers designs are discussed.