Length on waterline (LWL)

Length on the waterline, LWL, is the length of the hull measured along the design waterline from the forward intersection of the waterline with the stem to the after intersection with the stern or transom. It is the length that governs wave-making: the wave-resistance hump and the displacement hull-speed limit both scale with LWL through the Froude number Fn = V / sqrt(g times LWL). LWL therefore enters the speed-length ratio, the displacement-length ratio, and most resistance methods directly. It usually differs from both LOA (which adds overhangs) and LBP (between fixed perpendiculars); on a raked-stem or immersed-transom hull the three lengths differ by several percent, so the basis must be stated.