To complete the conning tower, get a 5- or a 7-inch length of pipe; bend over one end a little; thread it and screw in a bicycle valve. Finally stick the other end of the pipe through the hole in the top of the conning tower and solder it there, as shown in [Fig. 20], which also shows the conning tower complete. The purpose of this pipe is so that you can pump air into the tank with a bicycle, or an auto pump.

FIG. 20. THE CONNING TOWER OR COMPRESSED AIR TANK.

Screw the conning tower on the end of the pipe of the air-valve mechanism which projects through the top of the deck, and then you are ready to do something else.

FIG. 21. THE BRASS PROPELLER.

Setting the Propeller.—A 2½-inch brass propeller with three blades can be bought for about 40 cents of Luther H. Wightman and Co., 132 Milk Street, Boston, Mass.

FIG. 22. THE RUDDER AND PROPELLER.

This little propeller has a hub diameter of 5/16-inch, as shown in [Fig. 21]. When you get it, drill a 3/32-inch hole through the hub and thread it; screw it on to the end of the propeller-shaft, and then screw on a nut to hold it on tight. (See [Fig. 22].)