Recent research development on a bivortix vertical axis propeller

Preliminary tests on a vertical axis propeller model, with a double blade system are presented in reference [1]. The functioning of the system can be influenced by many parameters, such as the blades geometrical features, the number of blades of each rotor, their positioning on the hull, the number of propeller revolutions, the boat speed and the engine power. A series of full scale systematical tests with varying parameters was carried out, in order to define their effect on the behaviour of the global propeller. After having defined the testing procedures, the efficiency and the Thrust/Engine Power ratio were obtained for every condition. Subsequently, by changing the foil profiles and the position of the propeller on the boat, a series of improvements and investigations are described. The characteristics of the blades have been investigated by tests carried out, over the stall angle, in a small towing tank of Trieste University. A series of results are presented and discussed