Parametric Generation of Simple Hull Forms

When taking the first steps in a new ship design, the designer has few options for selecting a starting point for the hull lines: systematic series or transformation of the lines of another vessel. Both methods are widely used but have some known drawbacks. If the designer resorts to systematic series, the changing nature of preliminary design is likely to modify some of the hull's hydrodynamic coefficients (Cb, Cp, Awp, LCB, LCF,...) making difficult the application of the results (powering, seakeeping, etc.) of the parent hull. On the other hand, turning to a parent hull for the preliminary design of a vessel is also difficult as obtaining a good parent hull to transform may not be easy and in the end, the designer's experience is the most determinant factor. Some of these limitations can be alleviated with the use of parametric hull generation. This paper deals with the use of a simple parametric design method applied to simple hull lines such us sailing ship hulls and round bilge hulls. The described method allows the generation of hull lines that meet most of the hydrodynamic coefficients imposed by the designer, obtaining more flexibility than with normal affine transformations of a parent hull. The design technique is described in the paper and some application examples are showed. Introduction to more complicated parametric design methods is made. Parametric design is also a good technique to start numerical optimisation through CFD analysis, as far as it enables to create a range of variations of ship hulls that can be easily introduced in the CFD calculations.