DETAILS OF THE SCREW AND SCREW SHAFT.
476. Q.—What is the best method of fixing the screw upon the shaft?
A.—The best way is to cut two large grooves in the shaft coming up to a square end, and two corresponding grooves or key seats in the screw boss opposite the arms. Fit into the grooves on the shaft keys with heads, the length of which is equal to half the depth of the boss, and with the ends of the keys bearing against the ends of the grooves in the shaft. Then ship on the propeller, and drive other keys of an equal length from the other side of the boss, so that the points of the keys will nearly meet in the middle; next burr up the edge of the grooves upon the heads of the keys, to prevent them from working back; and finally tap a bolt into the side of the boss to penetrate the shaft. Propellers so fitted will never get slack.
477. Q.—What is the best way of fitting in the screw pipe at the stern?
A.—It should have projecting rings, which should be turned; and cast iron pieces with holes in them, bored out to the sizes of these rings, should be secured to the stern frames, and the pipe be then shipped through all. Before this is done, however, the stern post must be bored out by a template to fit the pipe, and the pipe is to be secured at the end to the stern post either by a great external nut of cast iron, or by bolts passing through the stern post and through lugs on the pipe. The pipe should be bored throughout its entire length, and the shaft should be turned so as to afford a very long bearing which will prevent rapid wear.
478. Q.—How is the hole formed in the deadwood of the ship in which the screw works?
A.—A great frame of malleable iron, the size of the hole, is first set up, and the plating of the ship is brought to the edge of this hole, and is riveted through the frame. It is important to secure this frame very firmly to the rest of the ship, with which view it is advisable to form a great palm, like the palm of a vice, on its inner superior corner, which, projecting into the ship, may be secured by breast-hook plates to the sides, whereby the strain which the screw causes will be distributed over the stern, instead of being concentrated on the rivets of the frame.