GB821824A - Improvements in or relating to variable pitch marine screw propellers - Google Patents

Abstract

821,824. Marine variable pitch propellers. SLACK & PARR (MARINE) Ltd. Dec. 15, 1955 [Dec. 16, 1954], No. 36411/54. Class 114. In a marine variable pitch propeller having three or more blades and in which pitch variation is effected by a control rod sliding in a hollow propeller shaft and carrying a crosshead linked to a crank arm or crank pin on the propeller blade root by a link capable of swinging movement about a centre fixed on the crosshead, a hub 14 bolted to a hollow propeller shaft 12 accommodates a crosshead 35 mounted on the end of a control rod 11 movable in the hollow shaft to displace the crosshead 35 along rods 33 supported between front and rear walls 34, 32 of the hub. The crosshead has a face 38 opposite each propeller blade root 21 the roots being secured to crank discs 25 carrying eccentric pins located in bores in links 40 the other forward ends of which receive pins on the crosshead : a raised portion of each face 38 acts as a stop to prevent excessive turning of the blade. The distance between the centres of these bores is substantially that of the eccentricity of the crank pins on the blade roots and the length of the crosshead is substantially within the area defined by the crankpin during a complete rotation. The pivotal connection on the crosshead for each link is offset from the propeller axis by a distance equal to the eccentricity of the crank pin on the blade root with the result that as the crank pins move from one side to the other of the plane of the axes of the propeller blades, the longitudinal centre lines of the links 40 remain substantially parallel to the propeller axis. The forward position of the crosshead corresponds to the full astern setting of the blades and vice versa. In assembling the hub the crosshead is passed through a radial bore 16 and bolted to the control rod and the blade root 21, held in its bearing housing 18 by the crank disc 25 which with the base of the blade-root engages a lip 22 on the housing, is thereafter bolted on the hub. In a modification, the bearing housing is omitted and the crosshead is inserted into the hub from the rear, the rear wall being made removable. The links 40 may be replaced by an arcuate groove 66, Fig. 9, in the crosshead, in which a block 65 carrying the crank pin 63, slides, the groove being centred about a point 69 displaced from the propeller axis by an amount equal to the eccentricity of the crank pin.