A perturbational study is made of the bow flow field with spray phenomena around a planing plate with a small dead rise angle and a small trim angle in order to get basis on the configuration of the wetted surface area. It is set forth a hypothesis such that the plate planes on a water surface deformed as a parabolic cylinder with transverse curvature near the bow, but the deformation probably seems to be caused by displacement effect. The hypothesis allows to assume a similarity flow changing the scale of transverse section as a square root of longitudinal length. The flow field is divided into three regions for the analysis. By analyzing the bow near field, the spray root line is obtained as forming a parabola on the plate, so that good coincidence with an experimental result of pressure contour is shown with help of the same flow near the spray root line as Wagner's local flow. The spray flow developing on the plate outside the spray root line is analyzed. The flow rate and thickness of the spray and the spray drag show good coincidence with an experimental result. Spray edge line is shown by assuming a lower bound of spray thickness.