Boys' Book of Model Boats

by Raymond F. Yates

To make a simple propeller, first cut out of thin sheet brass three blades as shown at A, [Fig. 37]. Sheet brass with a thickness of ¹/₃₂ inch is very suitable for this purpose. Next, a block, as shown at B, is carefully carved out so that the propeller can be hammered down into the depression. The same block is used for the three blades, so that each will have the same curvature. The block should be cut from oak, since this wood will not split or lose its shape when the forming is done.

The hub is made next. This is shown at C, [Fig. 37]. The hub, of brass, is made according to the stream-line method. It is filed to shape from a piece of round brass stock. A hole runs lengthwise in the brass, as shown, and a set-screw is used to hold the hub of the propeller-shaft. The method of cutting the slots in the hub is shown at D, [Fig. 37]. The hub is clamped between two boards placed in the vise, and a hacksaw is used to cut a slot in the hub. The hub is then turned around one third of a revolution, and another slot cut, using the same saw-marks in the boards, so that the angle of the second slot will be the same as the first one. The third slot is cut in the same manner. The three blades that were cut out are now fastened in these slots and held there by solder. This completes the propeller and it is now ready to be fastened upon the propeller-shaft.

Let us consider the general method of putting the propeller-shaft in place. The young boat-builder will readily understand that it would be very impractical merely to bore a hole in the hull of the boat to put the propeller-shaft through. In this way water would surely leak into the hull and the boat would sink in a short time. Some method must be evolved to keep the water out of the hull, and yet allow the propeller-shaft to revolve freely.

The propeller-shaft is arranged within a brass tube, as shown at [Fig. 38]. The brass tube should be about ¹/₈ inch larger in diameter than the propeller-shaft. A little brass bushing must also be arranged at each end, as shown. When the propeller-shaft is mounted in place in the tube, there will be a space between it and the tube. Before the propeller-shaft is put in place it is well smeared with vaseline, and when it is placed in the tube the space between the shaft and the tube will be completely filled with it. This will prevent water from entering. Owing to the fact that vaseline is a soft, greasy substance, it will not prevent the rotation of the propeller-shaft. The brass tube is placed through a hole bored in the hull of the boat. The hole should be a trifle smaller than the diameter of the brass tube, so that the tube can be forced into the hole.

One of the simplest methods of propelling a boat is by means of rubber bands. Such a boat is shown in [Fig. 39]. This is a small wooden hull fitted with a two-blade propeller. The propeller is shown at [Fig. 40]. It is cut in a single piece and held to the propeller-shaft merely by a drop of solder since there will not be much strain upon it owing to the low power of the rubber-band motor. The opposite end of the propeller-shaft is bent into a hook, and the rubber bands run from this to another hook placed at the bow of the boat. The rubber bands may be similar to those employed by model airplane builders. The motor, of course, must be wound up by turning the propeller around until the bands become twisted into little knots, as shown at [Fig. 39]. Boats driven by rubber bands cannot be very large unless a great number of rubber bands are used. Even then the power is short-lived. However, building a few small boats driven by rubber-band motors will do much to teach the young boat-builder some valuable lessons in boat construction.

Probably the best method of propelling model boats is the electric method. By building a boat large enough to accommodate two dry batteries or a small storage battery and a little power motor, a very reliable method of propulsion is made possible. The boat must have sufficient displacement to accommodate the weight of the dry-cells and storage battery. A boat two feet long, with a beam of 4¹/₂ inches, is large enough to accommodate one dry-cell and a small motor, providing the fittings of the boat are not too heavy.

A suitable power motor for small boats, which will run with either one or two dry-cells, is shown in [Fig. 41]. The connections for the motor are given clearly in [Fig. 42], and a suitable switch to control the motor is shown at [Fig. 43].

Owing to its greater power, the storage battery is to be preferred. Dry-cells are extremely heavy and occupy considerable space. They are also costly, since they do not last long and cannot be worked too hard unless they polarize.