Still another method of driving the propeller is illustrated in Fig. 48. This method is so simple that the author feels explanation to be unnecessary.
Clockwork can often be employed for propulsion purposes, but this method is not very satisfactory. It is also very difficult to obtain suitable clockworks to install in a boat. Oftentimes it will be possible to salvage the works of an old alarm-clock, providing the main-spring is intact. It is a very easy matter to mount the clock-spring and connect it to the propeller. Any one of the aforementioned methods can be employed.
Steam propulsion has its advantages; but, on the other hand, the writer is not inclined to recommend it as strongly as the electric method for reliability. Of course, steam is a more powerful agency in the propulsion of small boats and thereby greater speed is attainable by its use.
Here is a very simple small power plant suitable for driving boats up to 3-1/2 feet in length. The boiler is shown in Figs. 49 and 50. The method of assembling the boiler is pictured clearly in Fig. 49. A brass or copper tube about 2-1/2 inches in diameter is used. Two end pieces are cut to shape and forced into the boiler ends. A hole is drilled in the center of these pieces before they are put in place. After the end pieces are forced in place solder is carefully flowed around their edges. The brass rod is then threaded at each end and placed concentrically within the boiler, as shown in Fig. 49. A nut is placed on each end of this rod and tightened. The nut is then soldered in place. This brass rod, called a stay-rod, prevents the end of the boiler from blowing out when the steam pressure has reached its maximum value. Three holes are drilled in the brass tube, as shown. One is to accommodate the steam feed-pipe that goes to the engine; another is for the safety-valve, and still another for the filling plug. The safety-valve and filling plug are both shown in Fig. 51. The little spring on the safety-valve is adjustable, so that the valve can be regulated in order to prevent it from blowing off at pressures lower than that at which the engine operates.
A suitable firebox for the boiler is shown clearly in Fig. 52. This is cut to shape from stovepipe iron and held together with small rivets. Holes should be punched or drilled in the side of the firebox to give the burner a sufficient supply of air. The burner is illustrated clearly in Fig. 52. The fuel-tank can be made from an ordinary tin can with the cover soldered on, and a hole made for a cork by means of which it is filled with denatured alcohol. A little pipe runs from the fuel-tank to the burner. It is advisable, if possible, to place a small valve in this pipe to cut off the fuel supply when necessary. The only other method of putting the burner out would be to stand it on its end. The burner consists of a rectangular tin box with a top cut out as illustrated. A piece of brass or copper gauze is placed in the top. Asbestos wool is used to fill the can, and the alcohol is drawn into the wool by capillary attraction, where it burns with a steady hot flame at the surface of the copper gauze. In the corner of the can near the feed-pipe another small piece of copper gauze is soldered as shown. This covers up the feed-pipe entrance so that the asbestos will not plug up the pipe.