A comprehensive experimental work is done to investigate sloshing dynamics in a partially liquid-filled baffled tank, equipped with a floating barge. An aspect ratio(hs /l, liquid depth, hs to length of tank, l) of 0.488 (above critical fill level), which corresponds to 75% fill level, is considered. The barge was subjected to regular wave excitations with a wave height of 0.1 m and frequencies ranging from 0.45Hz to 1.54Hz under beam sea condition. In addition, porous baffles are placed inside a rectangular tank to study its effectiveness in reducing the sloshing energy. Three different porosities of 15%, 20.2% and 25.2% at l/2 are considered. The effectiveness of baffles is explored and the salient results for a single porous baffle are discussed. It is learnt that the effect of baffles on sway and roll responses is significant, whereas it is insignificant on heave. Porous baffles are effective in suppressing the sloshing oscillation in the vicinity or at wave excitation, fw =f 1, whereas the sloshing is amplified at fw =f 2 and fw =f 3 due to the resonance condition of modified natural frequencies. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.