By the strong wind in March, 1 set (two sheets) of module used as hull roof of the experimental solar fishing boat moored to the pontoon was blown away. Then, in order to investigate the hydrodynamic property of a hull roof, we manufactured model roofs, conducted a wind tunnel experiment and a flow visualization experiment, and examined some various effective measures. Furthermore, based on the result, a repair work is given to the roof of the boat and it is under observation now.