The Mega-Float project of the Ministry of Transport of Japan was undertaken with the aim of developing huge, off-shore structures of several kilometers in length, having a durability of at least one hundred years. It is considered that huge floating structures have the advantage of having less affect on the flow fields around them because of their small draft to depth of water ratio. The effect on tidal currents due to the Mega-Float has been verified as being very small by the results of several kinds of experiment which were carried out as collaboration research programs with the Megta-Float Technical Association and the Chugoku National Industrial Research Institute.