Model of a Lifting Screw

Model of a screw case in a stern with an elliptical transom. The screw lifting device consists of a loose frame with a two-bladed screw, which can be raised and lowered in the case by a rope running over two sheaves at the top of the screw case and two sheaves in the screw frame. The screw shaft has a hexagonal end that fits into the screw. The screw is disengaged by pulling the shaft into the ship, for which a lever mechanism driven by a rack and pinion with a worm gear is installed in the ship; the shaft can be shortened by a telescopic section behind the gear. The screw frame moves on vertical rails against the sternpost and the rudder post, which are fitted with teeth; into these fall pallets of the screw frame that prevent it from sliding back. The pallets can be held back by pulling on two ropes, allowing the screw frame to lower. A beam placed against the sternpost and clamped with bolts locks the movement of the screw frame when lowered.