Answer
The actual area under the sheer curve is compared with the area under a standard parabolic curve. The aft ordinate of which (SA) is given by 25((L/3) + 10) mm and the forward ordinate (SF) by 2SA mm.
The correction for deficiency or excess sheer is the difference between the actual sheer and the standard sheer multiplied by ((0.75 – S)/ 2L), where S is the total mean enclosed length of superstructure.