IMPROVED FLUID DISPLACING BLADE

A propeller (11) having five blades (13) supported from a hub (14) is exemplified. The propeller (11) is shown with the faces (15) of those blades (13) facing the viewer (out of the page), and has apertures (19) extending through each blade (13) from the face (15) to the back of each blade (13), a nd spread relatively evenly across the extent of each blade. The axial extent o f the apertures (19) is substantially aligned with the direction of movement o f the blades (13) relative to the axis of the propeller (11). The apertures (1 9) are normal both to the radial extent of the propeller (11) and the axial extent of the propeller. Each aperture (19) includes a bevelled edge in the form of a countersunk lip (21) extending around the periphery, on the face (15). The flow of fluid through the apertures (19) is believed to interfere with turbulent fluid adjacent to the back of the propeller (11), and so lead to improved efficiency of the propeller.