MAN B&W Controllable pitch propeller. High skew
To suppress cavitation-induced pressure impulses even further, a high skew design can be supplied, fig. 20 (a). By skewing the blade it is possible to reduce the vibration level to less than 30% of an unskewed design. Because skew does not affect the propeller efficiency, it is almost standard design on vessels where low vibration levels are required.
Today, the skew distribution is of the “balanced” type, which means that the blade chords at the inner radii are skewed (moved) forward, while at the outer radii the cords are skewed aft. By designing blades with this kind of skew distribution, it is possible to control the spindle torque and thereby minimize the force on the actuating mechanism inside the propeller hub, fig. 20 (b).
For high skew designs, the normal simple beam theory does not apply and a more detailed finite element analysis must be carried out, fig. 20 (c).
Fig. 20. a) high skew design; b) spindle torque; c) finite element calculation of propeller blade.