Abstract: Based on variational design theory, this paper proposed a variational ship lines design model, which could express and design ship lines. A computer aided design(CAD) method for designing ship lines with variational ship lines design model was described, which includes the data management, the definition of mathematical model, the establishment and modification of threedimensional model. First, the mathematical model defines the geometric positions and the geometry topology relations of the lines design elements; and then according to the mathematical one, threedimensional model can be built and modified; finally, ship lines design will be finished. Ship lines can be rebuilt quickly based on the variational ship lines design model, which can avoid the redesign and effectively improve the quality and efficiency of the lines design. The example, in which is described that ship lines are expressed and designed by variational ship lines design model, proves the practicability and advancement of the model.

Key words: ship lines, variational design, mathematical lines model, threedimensional lines model, computer aided design(CAD)