The variable-pitch propeller blades for the Vosper-Thornycroft VT1 hovercraft are cast in Ferralium® 255 (UNS S32550, Alloy 255, DIN 1.4507, ASTM F61), a super duplex stainless steel increasingly specified for marine applications where mechanical strength, toughness and corrosion resistance are essential to a long, efficient service life.
The application
The VT1 was designed for propulsion by water propellers mounted on skegs beneath the craft, giving good manoeuvring at slow speed in crosswinds. These K.M.W./Stones variable-pitch propellers were used in the VT1 operating between Malmo and Copenhagen in the summer of 1972.
The castings
The blades are fine examples of production machining, with an excellent surface finish that reflects the high quality of the castings. Each screw blade weighs 16lb and the complete screw has a diameter of 25 inches. In service it completed some 100 hours of trouble-free operation.
