The ship is divided into a number of equal-length sections (stations) along its length. For each section:

• Weight curve: the weight of the ship (hull, machinery, cargo, ballast, stores, etc.) in each section is determined and plotted as a stepped or smooth curve of weight per unit length against position along the ship. The total weight equals the displacement.
• Buoyancy curve: the buoyancy (displacement) of each section is determined from the hull form (the volume of the section below the waterline, from the Bonjean curves or the hydrostatic data) and plotted as a curve of buoyancy per unit length against position. The total buoyancy equals the displacement.
• Load curve: the load (net load) is the difference between the weight and the buoyancy in each section, i.e. load = weight - buoyancy. It is plotted as a curve of load per unit length against position. Where the weight exceeds the buoyancy the load is positive (downward), and where the buoyancy exceeds the weight the load is negative (upward).

Relevant features: the weight and buoyancy curves are stepped (discontinuous) because the weights and buoyancy are lumped in sections; the load curve is the difference and shows where the ship is loaded or buoyant; the total area under the load curve is zero (the total weight equals the total buoyancy); the load curve is the basis for the shear force and bending moment curves.

The shear force at any section is the algebraic sum of the loads (weight - buoyancy) to one side of the section, i.e. the integral of the load curve. Starting from one end (where the shear force is zero), the shear force is built up by integrating the load curve along the length; it is zero at the ends and reaches a maximum where the load curve changes sign (where the net load is zero). The shear force curve is the integral of the load curve.

The bending moment at any section is the integral of the shear force curve, i.e. the algebraic sum of the moments of the loads to one side. The bending moment is zero at the ends and reaches a maximum where the shear force is zero (where the shear force changes sign). The bending moment curve is the integral of the shear force curve.

Features connected: the load curve is the derivative of the shear force curve, and the shear force curve is the derivative of the bending moment curve. The maximum bending moment occurs where the shear force is zero, and the maximum shear force occurs where the load curve changes sign. The curves are used to check the hull girder strength.