First thing that we will must see is wake. What is the cause of wake? So, far we have seen that, when a ship is moving in water, if I draw the ship like this, there is a boundary layer which develops around the ship and goes behind it. Here, if I draw a velocity profile along the y axis, then the water velocity will be constant, because there is no disturbance to flow in front of the ship or very near the front because there is no boundary layer developed in the front of the ship. Let us consider a submerge part, no wave effect.