Boys' Book of Model Boats.

by Raymond Francis Yates.

PREFACE

EVERY boy likes to build boats. The interest in boats seems to be born in the race. The little three-year-old chap is instinctively attracted by a puddle of water in which to sail his "boat," which may take the form of a piece of shingle or common board. Few men have pa.s.sed through their boyhood days without having built boats at some time.

The author was an ardent boat-builder, and he well remembers how he combed the Children's Department of the local library in search of a book that would tell him something about boats, and especially for information regarding the construction of models. He found books on model airplanes, toys, electricity, radio, and chemistry, but alas!

nothing about model boats. He vowed then that when he became a man he would write a book on model boats--a book that would contain all the treasured information he had acc.u.mulated during his boat-building years.

This book is the result of that vow, and the author earnestly hopes that it will gladden the heart of every boy who builds and sails a boat.

There are probably few happier moments in a boy's life than when he sees his little model steamer proudly make her way across the park pond, or his little sail-boat respond to the summer breeze.

The author takes this opportunity to thank his wife, who acted as his amanuensis in the preparation of this ma.n.u.script.

RAYMOND FRANCIS YATES.

BOYS' BOOK OF MODEL BOATS

CHAPTER I

WHY A BOAT FLOATS

BEFORE taking up the construction of any of the model power boats described in this book, it will be well for the young boat-builder to become acquainted with such terms as buoyancy, displacement, center of gravity, etc. Knowledge of these subjects is more or less necessary if successful boats are to be made. Aside from this, they are terms that every boy who claims an interest in boats should understand.

"How does a steel boat float?" is a question that many boys ask. The reason they usually designate a steel boat is probably because steel is so much heavier than water. But many things heavier than water can be made to float if they are in the form of a boat. Concrete, for instance, is now being used in ship construction, and this substance, when reinforced with steel rods, is very much heavier than water.

Before learning how a boat floats, what is known as "specific gravity"

must be thoroughly understood. Gravity is a force that is continuously "pulling" everything toward the center of the earth. It is gravity that gives a body "weight." Some substances are heavier than others; or, to be more correct, it is said that the specific gravity of one substance is greater than that of another. It will be well to keep in mind that specific gravity merely refers to weight. It is simply a scientific term. The specific gravity of a substance is always expressed by a figure that tells how much heavier any substance is than water, because water has been chosen as a standard.

The specific gravity of water is 1. The specific gravity of gold is 19.26, meaning that it is about 19-1/4 times heavier than water. The specific gravity of a piece of oak is 0.86, which shows that it is not quite so heavy as water. One cubic foot of water weighs 62.42 pounds.

It will be understood that a cubic foot of gold would weight 19.26 x 62.42, because it is 19.26 times heavier than water. A cubic foot of oak, however, would weigh only 54 pounds, because it has been found that it has a specific gravity of only 0.86 which is less than water.

[Ill.u.s.tration: FIG. 1]

A cubic foot of oak (see Fig. 1), with a weight of 54 pounds, will float when placed in water. The cubic foot of bra.s.s (_B_), however, will not float, because it weights 8.1 times as much as water. For the present, then, it can be said that a substance lighter than water will float in water, but that substances heavier than water, such as iron, lead, gold, silver, etc., will not float. If the cubic foot of oak (_A_) were placed in water, it would sink to the depth shown at _C_. When the block sinks into the water, a certain amount of water will be forced away or "displaced"; that is, the block in sinking occupies a s.p.a.ce that was previously occupied or filled with water. The oak block sinks to within a short distance of the top because the oak is really just a trifle lighter than water. If a pine block were placed in the water it would sink only to the distance shown at _D_, since the weight of pine is less than oak, or only 34.6 pounds per cubic foot. A pine block will, then, displace only about 34.6 pounds of water, which leaves nearly half of the block out of the water. Thus, it will be seen that for a given volume (size) a cubic foot of wood will sink to a depth corresponding to its weight. Different kinds of wood have different weights.

If a cubic foot of bra.s.s is placed in water, it will sink rapidly to the bottom, because the bra.s.s is much heavier than water. How is it, then, that an iron or concrete ship will float? If the cubic foot of bra.s.s is rolled or flattened out in a sheet, and formed or pressed into the shape of a boat hull, as shown in Fig. 2, it will float when placed upon the surface of the water. Why is it that bra.s.s is caused to float in this way, when it sank so rapidly in the form of a solid square?

[Ill.u.s.tration: FIG.2]

It will be remembered that the pine and oak block were caused to float because they displaced a greater weight of water than their own weight.

This is just what causes the bra.s.s boat-hull to float. If the amount of water actually displaced by the hull could be weighed, it would be found that the weight of the water would be greater than the weight of the hull. It will be understood that the s.p.a.ce occupied by the bra.s.s boat-hull is far greater than the s.p.a.ce occupied by the block of bra.s.s before it was rolled out and formed into a hull. What is true of bra.s.s holds true of iron, steel, etc. A block of steel will not float, because the water it displaces does not weigh nearly as much as the block. If this block, however, were rolled out into a sheet and the sheet formed into a hollow hull, the hull would float, because it would displace a volume of water that would more than total the weight of the steel in the hull.

In the case of the bra.s.s boat-hull, it would be found that a greater portion of the hull would remain out of the water. The hull, then, could be loaded until the top of it came within a safe distance from the water. As the load is increased, the hull sinks deeper and deeper. The capacity of big boats is reckoned in tons. If a boat had a carrying capacity of ten tons it would sink to what is called its "load water-line" (L.W.L.) when carrying ten tons. As a load or cargo is removed from a vessel it rises out of the water.

What if the hull of a boat has a hole in it? If the hole is below the water-line, water will leak in and in time completely fill the inside of the hull, causing the boat to sink. Also, if too great a load or cargo were placed in a boat, it would sink. It must be understood that water leaking into a boat increases its load, and if it is not stopped it will cause the boat to sink.

The center of gravity of a boat is a very important matter. First, attention will be directed to the meaning of "center of gravity." If a one-foot ruler is made to balance (as shown in Fig. 3) at the six-inch mark, the point at which it balances will be very close to the center of gravity. The real center, however, will be in the middle of the wood of which the rule is composed. It should constantly be kept in mind that this "center of gravity" is a purely imaginary point.

Look at Fig. 4. If wires are arranged in a wooden frame, as shown, the point where the wires cross will be the center of gravity if the square formed by the wooden strips is solid. Every body, no matter what its shape, has a center of gravity. The center of gravity is really an imaginary point in a body, at the center of its ma.s.s. Oftentimes engineers are heard saying that the center of gravity of a certain object is too high or too low. Fig. 5 shows the center of gravity in a boat. If the center of gravity in a boat is too high (as ill.u.s.trated in Fig. 6) the boat is said to be topheavy and unsafe. When a boat is topheavy or its center of gravity is too high, the boat is liable to capsize. In fact, some very serious marine accidents have been caused by this fault.

[Ill.u.s.tration: FIG. 4]

[Ill.u.s.tration: FIG. 5]

[Ill.u.s.tration: FIG. 3]

[Ill.u.s.tration: FIG. 6]

The center of gravity (or center of weight) in a boat should be as low as possible. A boat with a low center of gravity will be very stable in the water and difficult to capsize. This is true of model boats just as much as it is true of large boats. The model boat builder must keep the weight of his boat as near the bottom as possible. For instance, if a heavy cabin were built on a frail little hull, the boat would be very unstable and would probably capsize easily.

CHAPTER II

THE HULL

MODEL boat-hulls are generally made by one of two methods. One method is that of cutting the hull from a solid piece of wood. The other method is commonly known as the "bread-and-b.u.t.ter" system. The hull is built up of planks laid on top one of another with marine glue spread between them.

The last-mentioned method (which shall hereafter be called the built-up method) possesses many advantages over the first.

Cutting a model boat-hull from a solid piece of wood is by no means a simple or easy task, especially for beginners. Of course, after several hulls have been produced in this fashion, the worker becomes practised in cutting them out.

[Ill.u.s.tration: FIG. 7]

[Ill.u.s.tration: FIG. 8]

The construction of hulls on the built-up principle will be described first. For the sake of convenience, the drawings of the boat-hull shown in Figs. 7 and 8 will be followed out. Before going further it will be well to understand drawings of boat-hulls; that is, how to know the lines of a boat from a drawing. By the "lines" is meant its shape.

Marine architects employ a regular method in drawing boat-hulls. Fig. 7 shows the side of a boat and half of the deck plan. It will be seen that this drawing does not tell much about the real shape of the boat, and if a hull were to be produced according to the shape given, the builder would have to use his own judgment as to the outline of the hull at different places. For convenience, the boat is divided into ten sections, represented by the lines 0 to 10. It will be seen that the shape of the hull at section 2 will be different from the shape of the hull at section 8. Again, section 0 will be much narrower than section 5.

[Ill.u.s.tration: FIG. 9]

Now look at Fig. 8. Note the shape of the cross-section of the hull at the different sections. For instance, the line at section 1 in Fig. 8 represents the shape of the hull at section 1 in Fig. 7. It must be remembered, however, that this is only half of the section, and that the line 1 in Fig. 8 would have to be duplicated by another line to show the true shape. The cross-section of the boat at section 0 is shown in Fig.

9. One half of the drawing in Fig. 8 represents the forward half of the hull, and the other half represents the stern half of the hull. If the shape of the boat at section 10 is desired, the line 10 in Fig. 8 could be traced on a piece of tissue paper. The paper could then be folded in half and the line first made traced on the second half. This would then produce the section of the boat at point 10. Thus, by closely examining Fig. 8 the shape of the entire hull can be seen.

[Ill.u.s.tration: FIG. 10]

If pieces of wire could be used to form the lines of the hull at the various sections, it would appear as shown in Fig. 10 when a.s.sembled.