Breadth at the design waterline (BWL)

The breadth at the design waterline, BWL, is the maximum beam measured at the design (load) waterline, as distinct from the molded breadth at the widest point of the hull, which may be reached above the DWL on a flared hull. BWL is the beam that enters waterplane and form calculations: the waterplane area coefficient Cwp uses the waterplane area over LWL times BWL, and BWL feeds the transverse waterplane inertia and hence BM and initial stability. It also drives the wave-making length-beam and beam-draft ratios used in resistance estimation. Because stability and waterplane properties depend on the beam actually at the floating waterline, BWL, not the deck-edge breadth, is the correct figure for hydrostatics at design draft.