Forward perpendicular (FP)

The forward perpendicular, FP, is the vertical reference line through the point where the design (summer load) waterline cuts the fore side of the stem. It is the forward origin of the ship’s longitudinal coordinate system: the length between perpendiculars, LBP, runs from the FP aft to the after perpendicular, and station 0 (or station 20 in a 20-station scheme) sits at the FP. Class and load-line conventions fix the FP at the stem-waterline intersection so that LBP, the length the rules use for scantlings and freeboard, is defined unambiguously regardless of bow overhang or a raked stem. The forward draft mark is read at, or corrected to, the FP for draft surveys and trim.