In order to obtain an analytical solution of the lift acting on a ship hull running with the drift angle, slender bpdy theory is reviewed and extended for analizing the flow around a slender body with wake. As a result, a new flow model is presented to calculate the linear and nonlinear terms of the lift analytically. In this flow model, the wake is represented with a vortex pair behind the transverse section of the slender body and then, the strength of it is determined by making an assumption to keep it on the Fopple line, so that the so called Lagally force acting on the body is equal to zero. Therefore, we can obtain the differential lift from the change of momentum in each section of the slender body. Finally, the comparison between the lifts calculated by present theory and the experimental results of model tests are shown to confirm its usefullness and accuracy. It seems to be fairly good.
