As containerships are built with larger size and faster speed for economic benefit, they are suffering more cavitation problem on propeller and rudder. Ship trial observation and drydock inspection show rudder cavitation can be a real problem of ship operation and maintenance. As is well known, a rudder operating behind a propeller can experience large onset flow angle along the rudder span. At a given speed, the maximum rudder angle before cavitation may be substantially higher in turning to one direction than to the opposite side. At high speeds, rudder can experience severe surface cavitation thereby causing detrimental erosion problem. To avoid or reduce cavitaton, a twisted rudder is proposed some years ago by US Naval and applied to a surface ship combatant. In comparing to non-twisted rudder, the cavitation inception envelope of twisted design is significantly wider and deeper. In this study, this twisted rudder design method is borrowed for a containership to improve its rudder cavitation problem. Comparison between non-twist and twist rudder is carried out to evaluate this twist rudder desigti concept.
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