A device for modifying a hull of a floating body of a floating vehicle or floating bridge, having a base floating body, with an upper surface forming a principal rolling path, and first and second lateral surfaces. On each side of the base floating body, a first movable wall which is mounted so that it pivots on a lower part of the corresponding lateral surface of the base floating body, a second movable wall is mounted so that it pivots on the first movable wall, and a third movable wall is mounted so that it pivots about the second movable wall The three movable walls are arranged with respect to each other so that, in a folded position, the first movable wall is essentially parallel to the first lateral surface of the base floating body, and the second and third movable walls partially cover the upper surface of the base floating body. In a deployed position, the first movable wall delimits a volume between itself and the first lateral surface, the second movable wall extends the first movable wall and the third movable wall forms an additional path broadening the upper surface.