Various geometric modeling techniques for a hull have been developed with wide application of computer to the ship design. Up to now, they are used for the representation of the sculptured surface with the piecewise polynominal curves or surfaces for a conventional hull. In this paper, a convenient and accurate modeling technique that is instancing and blending of the geometry primitives is introduced for a non-conventional hull such as SWATH, trimaran, caisson etc. Geometric characteristics, hydrostatic particulars and stability of the definded hull are calculated.