Accompanied with the recent increase of allowable tank length of tankers, a problem on the transverse strength of tankers has been discussed. That is the increase of shearing deformation in such long wing tanks, and it is feared that the large deformation may cause trouble. Recently Prof. Yamakoshi and K.Kagawa proposed a general method to calculate the deformation of every wing tank and investigated the effects of the deformation on the stress distribution of transverse frame rings. In this paper the characteristics of the shearing deformation are clarified from other viewpoint and an approximate method for estimating the deformation are presented. And by using the approximate method the effects of swash bulkheads in the wing tanks on the shearing deformation are estimated.