LBP = Length Between Perpendiculars.
OFFICER OF THE WATCH
https://officerofthewatch.com/2012/02/09/ships-geometry-and-hull-definition/
The form of a ship’s hull can determine the majority of its attributes; stability characteristics; resistance etc. As a result the power needed for a certain speed can also be determined along with the ship’s seaworthiness; maneuvering capabilities and load carrying capacity.
The Length Between Perpendiculars (lbp) which is the distance measured along the summer load waterplane between the aft and fore perpendicular. The aft perpendicular is taken at the aft side of the rudder post and the fore perpendicular ‘is the vertical line that intersects the forward side of the stem with the summer load waterline.
The mid-point between the perpendiculars is called amidships or midships.