Aft Perpendicular

The aft perpendicular on a ship is an imaginary vertical line which is drawn between the forward side of the stern with the summer load waterline. However, it depends on the designer of the ship whether the aft perpendicular is drawn through the aft side of the rudder post or through the center-line of the rudder pintles. The length overall (LOA) is the distance between the fore and aft extreme points of the vessel and is the aft reference line for hydrostatic calculations.