Sectional area curve

The sectional area curve plots the immersed cross-sectional area of the hull at each station against length, from zero at the bow, up to the maximum near amidships, back to near zero at the stern. Its area equals the displaced volume, and its centroid fixes the longitudinal center of buoyancy (LCB). The ratio of the enclosed area to the bounding rectangle (maximum section area times length) is the prismatic coefficient Cp, which describes how the volume is distributed fore and aft and strongly affects residuary resistance. Naval architects fair the curve early to set the LCB and Cp, then derive the body-plan offsets to match it. A hollow forward shoulder or a full run shows directly in its shape.