Cubic number (CN)

The cubic number CN is the product of length, breadth, and depth, L * B * D, in meters, an early-design size parameter used in empirical formulas for lightship weight, steel weight, and building cost. It is a proxy for enclosed hull volume before a lines plan exists. Steelweight and outfit-weight regressions of the Watson-Gilfillan type are written as coefficients times CN raised to a power, calibrated against a database of similar ships. CN is not a hydrostatic quantity and carries no draft dependence, unlike block coefficient or the volume coefficient. It is one of the first numbers fixed in concept design and feeds the weight and cost estimate.