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Length between perpendiculars (often abbreviated asp/p,p.p.,pp,LPP,LBP orLength BPP) is the length of aship along the summer load line from the forward surface of thestem, or main bow perpendicular member, to the after surface of thesternpost, or main stern perpendicular member. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.[1]
Measuring to the stern post or rudder stock was believed to give a reasonable idea of the ship’s carrying capacity, as it excluded the small, often unusable volume contained in its overhanging ends. On some types ofvessels this is, for all practical purposes, a waterline measurement. In a ship with raked stems, naturally that length changes as thedraught of the ship changes, therefore it is measured from a defined loaded condition.