In recent years floating breakwaters are considered for creating calm basin under open sea conditions for short period of time. In this paper, experimental studies on the performance characteristics of a horizontal floating plate breakwater are presented. The results of this two-dimensional model study are for regular waves of shallow and intermediate water depths. Analysis of the results shows that the transmission coefficient is strongly influenced by wave steepness and relative length of breakwater. It is also found to be dependent, to a lesser extent, on the relative depth of draft. Mooring forces are found to increase with increasing wave steepness and relative depth of draft. The performance of this breakwater is compared with other types of breakwater reported by earlier workers. © 1982.