INTRODUCTION: FLOATING BREAKWATERS ARE STRUCTURES WHICH PROVIDE A SAFE BREATHING AREA FOR THE VESSELS BY REDUCING THE INCIDENT WAVE HEIGHT. FLOATING BREAKWATERS ARE SUITABLE ALTERNATIVE FOR RUBBLE MOUNDED BREAKWATERS IN THE SITUATION SUCH AS DEEP WATER, UNSUITABLE BED CHARACTERISTIC, HIGH SEDIMENTATION, ETC   WHEN THE INCIDENT WAVE PERIOD IS LESS THAN 5S. TRANSITION COEFFICIENT (RATIO OF THE TRANSMITTED WAVE TO THE INCIDENT WAVE) IS USED TO EVALUATE THE PERFORMANCE OF THESE STRUCTURES. EXPERIMENTAL STUDIES OF CARVER (1979) SHOWED THAT ADDING screen UNDER THE PONTOON HAS LITTLE EFFECT IN REDUCTION OF TRANSMUTATION COEFFICIENT [1]. USING PHYSICAL MODELING HERMANSON (2008) CONCLUDED THAT TRANSITION COEFFICIENT WILL REDUCE UP TO 12% BY ADDING A screen UNDER THE FLOATING PONTOON [2]. REDUCTION OF TRANSITION COEFFICIENT BY INCREASING THE screen HEIGHT UNDER THE FLOATING PONTOON IN FLOATING BREAKWATERS IS ALSO REPORTED IN FOROOZANDEH’S (2006) EXPERIMENTAL STUDY [3]. IN CURRENT STUDY THE OPTIMUM screen HEIGHT IN screen ADDED PONTOON TYPE FLOATING BREAKWATERS IS SURVEYED ACCORDING TO THE DATA PROVIDED BY SOIL CONSERVATIVE AND WATERSHED RESEARCH CENTER.