PURPOSE: To provide an effective use of limited space at a small type vessel by using a part of goods retaining space as an adapter of a retainer by allowing the flat section which supports the bottom part of the goods to join to the hull for mounting the retainer.

CONSTITUTION: After a filler 31 is filled in the adhesive hole 30 of a flat section 22 of a retainer 20 and the position of the retainer 20 is determined, the rear side of the flat section 22 is joined with the hull 10 by FRP mat 28. For this work, since a step 26 is provided for the flat section 22, the goods retainer of the top flat surface 22 may be made flush after the plastic mat 28 is placed. The goods, for example the bottom of a fuel tank 18, is supported with the top plane of the flat section 22 to support a part of the side of the tank 18 with the connector 24 which is risen from the edge of the flat section 22. The tank 18 is hereafter, retained by a retaining belt which is connected with a hook 34 located on the rear of the connector 24. This enables to utilize the space, since a part of the space may be used for fixing with the hull.