Computer-aided Fairing and Direct Numerically Controlled Machining of Ship Hull Hydrodynamic Testing Models

Abstract

A computer-aided method of defining and machining 2-metre ship hull forms for hydrodynamic testing is described. The hull shape is faired from the original table of off-sets using a minimum number of smooth three-dimensional parametric skeletal-lines along the length of the boat. A fine set of smoothly blending station-lines is therby formed. The hull shape is preformed in two halves through a lamination process and machined on a three-axis numerically controlled machining (CNC) centre. A carbide-tipped, end-milling cutter is directed along the closely spaced station-lines to rapidly form an accurate hull shape requiring a minimum of hand work. The fairing and machining programs, called G-surf, run on a personal computer and are used to transmit the data and control the CNC machine in real time. The resulting hull shape is symmetrical and far more accurate than manually lofted and preshaped models.