Abstract
A variational principle is presented for solving the problem how we determine an unknown wetted surface of a planing ship in fixed condition. The functional of variational principle is not represented by the pressure distribution but loading function, circulation distribution around longitudinal sections, and the unknown wetted length distribution in order to avoid troublesome behavior of the pressure at the spray root line which is the boundary of the wetted surface. The extremal of the functional satisfies the lifting-surface integral equation and the elevated water surface condition along the spray root line, both are sufficient to determine the wetted surface. And also, an approximate functional actually determines well, regardless of adoption of trial function, the unknown wetted surface distribution of high aspect ratio planing plate.
