B - Operations – Transporting – 63 – H
Patent
B - Operations, Transporting
63
H
115/23
B63H 3/00 (2006.01)
Patent
CA 1127468
Improvements in marine propellers ABSTRACT A variable-pitch marine propeller comprises two or more helicoidal blades 6 which are mounted on a hub 1 so that each blade is free to pivot about a pivot axis 25 which extends radially outwards from the hub 1. The pivot axis 25 of each blade 6 is spaced in front, in the direction of rotation 24 of the propeller, of the centre of pressure of the blade 6 so that in operation, the water pressure acting on the blade 6 exerts a torque which tends to turn the blade 6 about its pivot axis 25 in a direction to bring the surfaces of the blade into line with the flow of water over the blade. The pivot axis 25 is also spaced behind with respect to the direction of movement of the axis of rotation of the propeller through the water, at least a major portion of the pressure surface of the blade so that, in operation, the resultant of the drag of the water on the blade exerts a torque which tends to turn the blade about its pivot axis 25 in an opposite direction. Additionally, and most importantly, the shape and mass distribution of the blades 6 relative to their pivot axes 25 is such that centrifugal effects tend to move the blades, in the absence of hydrodynamic forces, into a pitch equal to that of the helicoid. The various torques acting on the blades are such that, in operation, over a range of rotational and axial speeds, each blade 6 adopts a stable equilibrium position in which its pitch is optimally suited to the speed of rotation and the linear axial speed of the propeller.
356924
Fetherstonhaugh & Co.
Woodcoxon Engineering (international) Limited
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