The after perpendicular, or aft perpendicular, noted AP, is a line drawn perpendicularly to the load line through the after side of the rudder post or through the axis of the rudder stock.
Today for some merchant vessels ships, it is usual to place the AP at the intersection of the aftermost part of the moulded surface and the load line.
The forward perpendicular, FP, is drawn perpendicularly to the load line through the intersection of the fore side of the stem with the load waterline.
Points to pounder for forward and aft perpendicular
- While all moulded dimensions are measured to the moulded surface, the F P is drawn on the outer side of the stem.
- The distance between the after and the forward perpendicular, measured parallel to the load line, is called length between perpendiculars and its notation is Lpp.
- An older notation was LBP.
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