This study investigate wave-structure interactions of a free surface semicircular breakwater in irregular waves using physical modeling. The hydraulic performance of the breakwater is evaluated in the forms of transmission, reflection and energy dissipation coefficients.Wave climate near the test model is also recorded and expressed in the formofwave disturbance coefficient.These hydraulic coefficients are evaluated with respect to the wave scattering parameter, relative breakwater immersion depth, wave steepness and wave spectrum type. The experimental results showed that the perforated free surface breakwater is an effective wave dissipater with low reflectivity. © 2013 Taylor & Francis Group, London.