Whenever a body moves in a fluid there is pressure force acting developed that is acting normal to the surface of the body.
Earlier we have seen that if the fluid is non-viscous and completely immersed, then the forward component of the pressure force would cancel with the aft component of the pressure (Ideal fluid in ideal scenario). But as the body comes up to the surface, the pressure developed around the body generates waves. This wave generation is dependent on the air-water free surface and gravity.
The net fore-and-aft forces upon the ship due to fluid pressure acting normal to all parts of the hull is the wave making resistance.