Continous optimization of Controllable Pitch Propellers for fast ferries

Nowadays Controllable Pitch Propellers (CPP) are employed on several ships whose speed is an important item of the desiderata. Significant examples are the large Ro-Pax, 27 ÷ 31 kn fast, connecting harbours at distance of 200 ÷ 700 nautical miles, or smaller fast ferries for inshore route sailing at the same speed range. It is well-known that CPP are employed because they are very suitable for harbour manoeuvring but induce a remarkable propulsive efficiency reduction at cruising speed. Moreover, many times, the fast ferries operating on inshore route sail at low speed or in shallow water conditions where thrust loading and speed of advance are different from the same quantity induced by the standard conditions. In this study we want to propose an active logic that, continuously, optimizes the configuration of the propeller according to the actual conditions of the ship. In particular, the logic and the control system, have the purpose to select the best pitch angle taking in account changes in resistance and wake. The working principle of the logic is based on the engine speed and the measure of the torque absorbed by the propeller, to obtain the actual self-propulsion coefficients. Based on these data, the controller identifies the pitch angle for the best performance of the propeller.