THIS invention relates to a propeller and more particularly, but not exclusively, to a propeller for use with inboard and outboard boat engines. The propeller includes a hollow hub and a plurality of primary blades extending substantially radially outwardly from the hub, with each primary blade including a blade face, a blade back and a root section. The propeller is characterized in that a set of secondary blades are provided inside the hub, and that an inner volume of the hub is in flow communication with a volume radially outwardly of the propeller hub.