Rudder for reduced cavitation

A method of twisting a rudder to substantially align said rudder with a direction of a fluid flow into said rudder, a resulting twisted rudder being located substantially about a vertical plane aft of a rotating ship propeller, said twisted rudder having a chord and a span, said chord and span defining a curved locus of points, said rudder operating in the fluid flow behind said rotating propeller, said rotating propeller imparting to the fluid flow an induced flow angle that varies in a spanwise and a chordwise direction, the induced flow angle defining an onset flow angle into said rudder, said method comprising the steps of:

• providing a plurality of rudder profiles extending between a leading edge and a trailing edge, each of said profiles having a mean chordline, said profiles spaced in a spanwise direction of said vertical plane and defining an untwisted rudder shape;
• providing a matrix of points in said vertical plane, said matrix comprising a plurality of points in each of said profiles such that said matrix defines a plurality of spanwise points and a plurality of chordwise points in said vertical plane, each of said profiles having associated therewith a thickness measured normal to said mean chordline at each of said plurality of points, said thickness varying between said leading edge and said trailing edge, each of said plurality of points defining a rotation point, said rotation points including a forward most rotation point and an aft most rotation point, each of said rotation points defining a corresponding rotation axis perpendicular to said profile at said rotation point;
• determining said onset flow angle behind said rotating propeller at each of said points in said matrix;
• and
• rotating each of said profiles sequentially from said forward most rotation point to said aft most rotation point about said corresponding rotation axes such that a rotated mean chordline is formed thereby and wherein a tangent to said rotated mean chordline at each of said rotation points defines a twist angle, said resulting twist angles being substantially equal to said onset flow angles at corresponding rotation points such that each of said rotated mean chordlines are substantially aligned with the direction of the fluid flow at each of said corresponding points in said matrix, further wherein each of said rotated profiles has associated therewith a rotated thickness measured normal to said rotated mean chordline at each of said rotation points, said rotated thickness at each of said rotation points being equal to said thickness measured normal to said mean chordline at each of said plurality of points, said rotating forming a plurality of rotated profiles defining said twisted rudder.