Design waterline (DWL)

The design waterline, DWL, is the waterline the hull floats on at its design (load) draft and displacement, the datum about which the principal hydrostatics, the lines, and the form coefficients are defined. LWL, BWL, the waterplane area, and the block, prismatic, and waterplane coefficients are all referenced to the DWL. It is the load condition the designer optimizes for resistance and the line at which the entrance angle and bulbous-bow geometry are tuned. On a commercial ship the DWL corresponds to the design draft used for the contract speed-power; class load-line marks then fix the deepest legal draft separately. On the lines plan it is the heaviest waterline, with parallel waterlines above and below at fixed spacing.