Abstract: As part of a testing service agreement with Walter Marine and Atlantic Reefmaker, a 1:5.2 physical model of the Reefmaker Wave Attenuator was constructed and tested by the US Army Engineer Research and Development Center to evaluate its influence on wave attenuation. The tested prototype wave periods ranged from 2.5 to 8 sec with prototype wave heights between 1 ft and 6.5 ft. The Reefmaker Wave Attenuator included orthogonal and square designs and was tested under a variety of configurations including a suspended configuration, a bed-mounted configuration, and a rotated configuration. Testing demonstrated that depending on configurations and wavelength, the wave transmission coefficients ranged from 0.29 to 0.70. The most improvement, however, was demonstrated when testing the square unit designs with transmission coefficients, kt, below 0.51. The smallest kt of 0.29 occurred during square unit testing, which consisted of eight bed-mounted, square Ecosystem disks plus a base unit (24.05 in. freeboard) and with a wave period of 3.0 sec and height of 0.84 ft. Of all 134 tests performed, including the suspended case, the average transmission through the structure was 58%.