Boys' Book of Model Boats Part 2

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These barges are so easy to construct that the model-builder should make three or four of them at a time. If the pieces for several are cut out at the same time, the construction will be just that much easier. If the boat does not sink far enough into the water, a piece of lead should be placed on the bottom to bring it down. This piece of lead should be placed as near the center as it is possible to get it. Otherwise the boat will list or tip at one end or the other. With a little patience and care the weight can be so adjusted on the bottom as to bring the scow to a perfectly level position. The reader will understand that the water-line of a scow or any boat made according to the directions in this book will depend largely upon the nature of the wood. In the first Chapter of the book it was pointed out that the specific gravity of different woods varies, and therefore the buoyancy will vary.

A model freighter is shown in Fig. 27. The hull of this boat can be formed by two 1-1/2-inch planks. These will require a little hard work to cut out; but, on the other hand, the effort will be entirely justified by the pleasing appearance of the little craft that can be produced in this way. A bow and stern block to raise the deck are cut out and nailed in place, as shown. A cabin is also placed on the stern of the craft, and this is formed by a block with a piece of cigar-box wood placed on the top. The cigar-box wood should project a little over the edges to form a canopy. The center of the deck can be raised by a third block; and three independent blocks, two large ones and a small one, form the main cabin. Sandwiched in between these blocks are three pieces of cigar-box wood. The remaining details of the craft are so simple that they may easily be made by following the diagram.

[Ill.u.s.tration: FIG. 29]

Let us turn our attention to model war-s.h.i.+ps. A torpedo-boat destroyer is clearly ill.u.s.trated in Figs. 28 and 29. This is very simple to construct and makes a pleasing craft when finished. The hull is formed by two blocks. One of these forms the raised deck on the bow of the boat. The cabin is built up on this raised deck. It will be seen that the part of the hull that rests in the water is formed by one block. In building boats of this nature the constructor should be careful to keep them long and slender, since torpedo-boat destroyers are always of this type. They are high-speed craft, and their displacement must therefore be as small as possible. Some of these boats carry four stacks and some two. The author prefers four stacks as giving the boat a better appearance than two. The two little cabins near the stern of the boat are placed there merely to take away the plainness of construction. The guns mounted forward and aft are merely round pieces of wood with a piece of wire bent around them and forced into a hole in the deck.

[Ill.u.s.tration: FIG. 30]

The boat-builder should not be satisfied with one or two of these craft; he should make a whole fleet. This will afford the average boy a great amount of pleasure, since he can add to his fleet from time to time and have official launchings. Each boat can also be given a name and a number. A little gray paint on the hull of these boats and black on the stacks gives them a very presentable appearance.

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A battles.h.i.+p is shown in Fig. 30. A battles.h.i.+p should be at least twice as long as a torpedo-boat destroyer. A view of the battles.h.i.+p as it will look in the water is shown in Fig. 31. By carefully examining this drawing the builder will be able to see just the number and shape of the blocks that enter into the construction of the craft. The battles.h.i.+p is provided with four main batteries mounted in turrets, one forward and three aft. A mast is also built, and strings run from it to the top of the main cabin and to the end of one of the turrets mounted aft. A screw is placed through the centers of the fore and aft turrets, so they can be turned to any position. Battles.h.i.+ps should be painted gray. It will be necessary to place rather a heavy keel on the boat just described in order to bring it down to the proper depth in the water. Otherwise it will be topheavy and will capsize very easily. A fleet of battles.h.i.+ps and battle-cruisers can easily be made according to the foregoing instructions, and the builder should not be satisfied with producing only one.

A pleasure yacht is ill.u.s.trated in Fig. 32. The hull of this craft is formed by two boards nailed together. The cabins are very simple, being formed by a solid block of wood with a piece of cigar-box wood tacked to the top. The windows and doors are marked in place with a soft lead-pencil, and the stack is mounted midway between the two cabins. A wireless antenna should be placed on the boat, with a few guy-wires from the masts run to various parts of the deck. A lead-in wire also runs down into one of the cabins. The hull of this boat should be painted pure white. The deck can be left its natural color, while the stack should be painted black and the cabins white with green tr.i.m.m.i.n.gs.

Almost any type of boat can be produced by the use of simple blocks of wood and other miscellaneous pieces easily brought to shape from ordinary materials. This method of construction offers a wonderful opportunity for the boy to exercise his creative faculties.

CHAPTER IV

STEAM AND ELECTRIC PROPULSION

BOATS are propelled by two different systems. Some inland-water boats still employ side paddle-wheels, while ocean-going vessels use the more modern propeller or screw.

The paddle-wheel really acts as a continuous oar. Such a wheel is shown in Fig. 33. As the wheel goes around the paddle dips into the water and pushes the boat forward. If the direction of the boat is to be reversed, the rotation of the paddle-wheels is reversed.

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Before pa.s.sing onto the screw, it may be well to explain just how a paddle-wheel causes a boat to move. When a man gets into a rowboat, he generally pushes himself off by placing his oar against the dock or sh.o.r.e and pus.h.i.+ng on it. That is just what the paddle does in the water.

It dips into the water and pushes against it. It must be remembered, however, that water is unlike a solid substance and it "gives." When a man places his oar against the bank and pushes it, the bank does not move, and all of the man's energy is used in starting the boat. Water, however, does not remain stationary when the paddles push against it, and therefore all of the power it not utilized in moving the boat--part is used in moving the water.

The paddle-wheel is not so efficient in moving a boat as the more modern propeller--or screw, as it is more often called. The screw receives its name from the ordinary metal screw, because its theory of operation is exactly the same. A wood screw, when turned, forces itself into wood. A propeller, when turned, forces itself (and thereby the boat) through the water. A small propeller is ill.u.s.trated in Fig. 34. This is an ordinary three-blade propeller. (The writer prefers the word propeller instead of screw.)

From the drawing, it will be seen that the propeller-blades are mounted at an angle. This angle of the blades causes them to force water back as they cut through it when the propeller is revolving. This forcing of the water back tends to produce a forward motion of the propeller, and in this way the boat on which the propeller is mounted moves through the water. The propeller is caused to revolve by a steam-engine, steam-turbine, or gasolene-engine, as shown in Fig. 35. Longer boats have more than one propeller. A boat that has two propellers is called a twin-screw boat. A boat driven with four propellers is called a quadruple-screw boat.

When a machine screw is turned around just once, it moves forward a certain distance, as a glance at Fig. 36 will show. The distance the screw moves forward will depend entirely upon the distance between the threads. The distance between the threads is called the pitch of the thread. If the threads are 1/32 inch apart, then the screw will move 1/32 inch every time it revolves.

If a propeller acts in the same way as a screw, then it too must have a pitch. The pitch, or the distance that a propeller will advance in one revolution, is measured in inches. A propeller with a pitch of ten inches should move ten inches through the water at each revolution.

However, there is a certain amount of "slip," and a propeller does not actually advance the distance that it should theoretically. The pitch of a propeller is really the distance it would advance in one revolution if it were revolving in an unyielding or solid substance.

To make a simple propeller, first cut out of thin sheet bra.s.s three blades as shown at _A_, Fig. 37. Sheet bra.s.s 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 bra.s.s, is made according to the stream-line method. It is filed to shape from a piece of round bra.s.s stock. A hole runs lengthwise in the bra.s.s, 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 bra.s.s tube, as shown at Fig.

38. The bra.s.s tube should be about 1/8 inch larger in diameter than the propeller-shaft. A little bra.s.s bus.h.i.+ng must also be arranged at each end, as shown. When the propeller-shaft is mounted in place in the tube, there will be a s.p.a.ce 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 s.p.a.ce 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 bra.s.s 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 bra.s.s tube, so that the tube can be forced into the hole.

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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 4-1/2 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 s.p.a.ce. They are also costly, since they do not last long and cannot be worked too hard unless they polarize.

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