This paper is a numerical investigation of incident wave interactions with a moored, pontoon-type floating breakwater. We employ a boundary element method to solve the diffraction and radiation boundary value problems describing the situation of a moored floating breakwater in waves. The numerical model includes the hydrodynamic and mooring analyses, verified by the previous numerical and experimental results. Using the numerical model, we are able to assess the hydrodynamic performance of a moored single and dual pontoon floating breakwaters in regular waves. In particular, the effects of the mean wave drift force on the mooring system and wave attenuation characteristics are examined. The numerical results show that mooring tensions are significantly influenced by the mean wave drift force. However, the effect of the drift force on the performance of the floating breakwater in regular waves is not as significant.