A Scalar Metric for Assessing the Producibility of a Hull Form in Early Design

Abstract

A scalar hull surface producibility cost metric is introduced as an area weighted sum of the relative cost of producing classes of hull surface plates. The classes include flat plate, within some small tolerance; plating with curvature of various magnitude in a single direction; plating with double curvature of various magnitudes; and plating with reverse double curvature of various magnitudes. The classification could also be extended to include the orientation of the primary stiffeners and include the cost of producing the stiffened hull surface panels. The normal curvatures of the hull surface are made available at a discrete mesh by current hull surface design software, such as FastShip or Maxsurf. The producibility metric uses this data with the manufacturing-based curved plating classification and relative production cost information from either expert opinion or shipyard specific cost data to produce a scalar metric which can be used by the hull designer to compare alternative hull designs. Due to the natural imprecision of the relevant cost data and the variability among manufacturing in different shipyards, a fuzzy logic approach is used to classify and estimate the relative cost of forming the plating of each element of the surface of the hull. The metric is implemented and tested in the C and PERL languages and will be implemented within the FastShip hull development system using a PERL macro.