Model of a Lifting Screw, Petrus van der Loo, 1857 Canvas Print
Model of a screw shaft between stern and rudder stems, with part of the keel and the rear apostles. The screwlighter consists of a separate frame with a screw, which can be hoisted up and down in the tube on a rope, which runs over a disc at the top of the screw sleeve and a disc in the screw frame. The screw is a Mangin screw, a four-bladed propellor, composed of two two two-bladed screws that can be put in parallel position for lighting. For this, the shaft of the rear screw, which runs through the axis of the front one, is provided with a slot at the back, which must be put in a vertical position in order to be able to lift the screw; the rails over which the slot runs immediately blocks the screw in the vertical position. The front screw is then in a horizontal position. Of these, the propeller shaft at the front has two intersecting slots, which fit over the same rail: halfway, between the lines A and B, this rail is interrupted, so that here the screw can be turned. The vertical rails against the stern and the screw stems over which the screw window moves are provided with teeth; this includes ratchets of the screw window that prevent slipping back. The ratchets can be held back by pulling two ropes, so that the screw window can sink. Scale 1:10 (derived).
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