Controllable pitch propellers systems today utilize pitch control of all the propeller blades at the same time depending on the wanted speed of the ship.
The problem with this is that the water velocity entering the propeller is not uniformly distributed over the propeller plane due to the hull of the ship. This is also called the wake field, which in principle is a description of the relative water velocity that enters the propeller plane. At the top of the wake field, for a single screw ship, the relative velocity of the water is at its lowest and at the bottom it is the highest.
Because of the difference in the relative velocity of the water at the top and bottom of the wake field the optimum pitch angle for the propeller blade changes depending on its position in the wake field. If the pitch of the propeller blades could be changed individually then the propeller blades could always have the optimum pitch angle which may increase the propeller efficiency.
Is it possible to make a system which is capable of turning the propeller blades individually such that it follows a pitch angle trajectory which increase the propeller efficiency and reduces cavitation and noise?