Considering a three dimensional disk with a circular or ringed or rectangular waterplane as a ship of shallow draft, hydrodynamic forces in shallow water in heaving mode are investigated. The boundary value problem is formulated by the use of the source technique so that integral equations for the source densities are obtained. Series expansion has been applied as the Green's function. In this paper, two kinds of numerical schemes are investigated, one restricted to axi-symmetric bodies such as a circular disk and a ringed plate and another as general source technique applied to a rectangular plate. The numerical calculations of added mass and damping coefficient by both methods give fairly good agreement with experimental results by forced oscillation technique. The authors also show the negative added mass and the wave free frequency for heaving ringed plate.