Experimental investigation on hydrodynamic effectiveness of a water ballast type floating breakwater

This paper proposes a new type of water ballast floating breakwater. The structure consists of a water ballast double floating box and a vertical plate, which uses several wave attenuation mechanisms. The hydrodynamic effectiveness which is presented as a function of the wave transmission coefficient is investigated experimentally. The action of 2D regular waves with wide ranges of wave heights and periods is considered. The motion responses of the floating breakwater without mooring line have also been measured. Emphasis is given on the effect of the incident wave characteristics, the height of the vertical plate, different draft, water or dry sand ballast, with and without top baffle. Comparison of the new structure is also made with other novel floating breakwaters reported in the previous literature. Experimental results show that ballasting with water in the floating box not only enhances the seakeeping performance of the floating breakwater, but also increases the incident wave attenuation when compared to dry sand ballast. Heightening the height of the vertical plate and/or the draft of the floating body is conducive to decreasing the wave transmission. Adding an extra baffle on the top of the floating body, however, does not seem conducive to the wave attenuation effectiveness. Compared to the previous well-known floating breakwater model, the water ballast type in this paper has competitive effectiveness.