PURPOSE: To prevent a wave from dashing on the deck of a ship at its sailing, by providing strut insertion pipes in the inside of bulwarks, erecting struts not at work and removably mounting insertion boards to grooved parts on both sides of the strut and on top faces of the bulwarks.

CONSTITUTION: In a small sized fishing boat made of Fiber Reinforced Plastics (FRP), strut insertion pipes 8 are secured in the inside of bulwarks 2 to form a frame, and struts 6 are vertically provided in said pipes 8, and insertion boards 7 are removably mounted to grooved parts formed on both sides of the strut 6 and on top faces of the bulwarks 2. At work for drawing up and down a net, the insertion board 7 is removed to perform an easy work, while at normal sailing the insertion board 7 is mounted to prevent a wave from dashing on a deck.