A water wheel can not have more than 75% of the blades in contact with water at any point (or it would slow it down) and it is rarely practical to have more tha

A water wheel can not have more than 75% of the blades in contact with water at any point (or it would slow it down) and it is rarely practical to have more than 30% of the blades in contact with water. A turbine in a vortex has 100% water-blade contact all the time, which means it can transfer more power with a smaller size and cheaper materials.