So, when you generate negative pressure on the back side, that negative pressure if it goes below the vapor pressure of water or their about, then it will cavitate. So, the negative pressure on the back of the blade, what does it depend on? It will depend on the blade shape, the kind of aerofoil section you have that is called thickness etcetera, it will depend on the water velocity and it will depend on the angle of attack, isn’t it? Angle of attack is directly related to lift, which in turn is directly related to negative pressure..