Hydrodynamic characteristics of a floating pontoon breakwater with triple vertical porous membranes are investigated, within the context of a two-dimensional linear wave-flexible body interaction theory. The vertical-porous-membrane structures are hinged with spacing at the bottom of a floating pontoon and also hinged at some distance from the seabed. The tensions in the membranes are achieved through the net buoyancy force, created by the submerged volume of the pontoon. A floating structure is partially restrained by linear symmetric moorings, placed both fore and aft. The restoring/exciting force and moment calculated by the tip displacements of membranes within the pontoon, has been formulated using appropriate boundary conditions. The BEM program is based on a discrete membrane dynamic model and simple-source (second-kind modified Bessel function) distribution over the four sub-fluid domain boundaries. Since the boundary condition on the membrane is not known in advance, the membrane motions and velocity potentials in each region are solved simultaneously. It is found that a properly moored floating pontoon breakwater, containing long vertical porous membranes, which take a major fraction of the water column, can significantly increase the overall wave blocking efficiency in normal and oblique incident waves, including long wave regions.