Quasi-developable BB-spline surfaces in ship hull design

The use of developable surfaces in ship design is of engineering importance because they can be easily manufactured without stretching or tearing, or without the use of heat treatment. In some cases, a ship hull can be entirely designed with the use of developable surfaces. In this paper, a method to create a quasi-developable BB-spline surface between two limit curves is presented. The centreline, chines and sheer lines of a vessel are modelled as BB-spline curves. Between each pair of these boundary curves or directrix lines, the generator lines or rulings are created and a quasi-developable BB-spline surface containing the rulings is defined. A procedure based on multiconic development is used to modify the directrix lines in case the rulings intersect inside the boundary curves, avoiding non-developable portions of the surface. BB-spline curves and surfaces are widely used today in practically all the design and naval architecture computer programs. Some examples of ship hulls entirely created with developable surfaces are presented.