Boys' Book of Model Boats Part 9

[Ill.u.s.tration: FIG. 127]

Fig. 127 shows the dry-dock with a model boat in position.

CHAPTER XII

OPERATION OF FLASH STEAM POWER PLANTS FOR MODEL BOATS

THE flash steam method of propelling model power boats of the racing type produces a far greater speed than would otherwise be possible.

Flash steam plants are far more complicated than ordinary steam-propelled power plants, and for this reason the author devotes a chapter to their description.

A considerable equipment of tools and not a little mechanical ingenuity are required to produce and a.s.semble a workable flash steam plant.

However, such plants have gained great popularity in the past few years, and all of the hydroplane racing craft are propelled with such outfits.

These power plants are capable of delivering such a tremendous power that speeds as high as thirty-five miles an hour have been reached by boats measuring 40 inches long.

The ill.u.s.tration, Fig. 128, shows a flash steam plant and its various parts. Each part and its function will be described in this Chapter in detail. The gasolene tank _A_ is used to hold the fuel, which is fed to the gasolene burner _C_. The gasolene burner operates on the principle of the ordinary gasolene torch. First the tank is filled about three-quarters full with gasolene. An air-pressure is then produced in the tank with a bicycle pump. The pipe leading from the gasolene-tank at the top is coiled around the burner, and the free end of it is bent and provided with a nipple, so that the gasolene vapor will be blown through the center of the helix of the coil formed by the pipe bent around the burner. This is quite clearly shown in the drawing.

[Ill.u.s.tration: FIG. 128]

The cylinder is merely a piece of stovepipe iron bent to shape and provided with several air-holes at the burner end. To start the burner, the vaporizing coils must first be heated in an auxiliary flame. The flame of an ordinary blow-torch is suitable for this purpose. After the coils have become sufficiently hot the valve at the top of the gasolene-tank is opened, and this causes a stream of gasolene vapor to issue at the nipple. This produces a hot flame at the center of the vaporizing coils, and in this way the coils are kept hot. The purpose of heating these coils is further to vaporize the gasolene as it pa.s.ses through them on the way to the burner. Once started, the action of the burner is entirely automatic. The vaporizing coils are made of Shelby steel tubing with an internal diameter of 1/8 inch.

It will be seen that the flame from the gasolene-torch is blown through the center of the boiler coils _B_. Thus, any water pa.s.sing through these boiler coils is instantly converted into steam. In other words, the water "flashes" into steam. The heat of the blow-torch is so great that most of the boiler coils are maintained at red heat even while the water is pa.s.sing through them.

Notice the water-tank _G_. A little scoop, formed by a pipe of small diameter, protrudes through the bottom of the boat, so that the forward motion of the boat will cause water to rise in the tank _G_. An overflow is also provided, so that, should the water not be sucked out of the tank quickly enough, it will not flood the boat. The overflow pipe hangs off the side of the boat.

The water pump _E_ sucks water from the tank, and pumps it through the check-valve _K_ (this valve permits water to pa.s.s in one direction only) into the boiler coils. The boiler coils, being red-hot, cause the water to flash into steam the instant it reaches them. By the time the steam has reached the opposite end of the boiler coils, it is no longer steam, but a hot, dry gas at a terrific pressure. From the boiler coils the steam pa.s.ses into the steam-chest of the engine, and thence into the cylinder, where it expands, delivering its energy to the piston.

It will be seen that the water-pump _E_ is geared to the engine. Owing to this, it is necessary to start the water circulating through the boiler coils by the hand pump _F_. This hand pump forces water through the boiler coils just as the power pump does. After the hand pump is started the engine is turned over a few times until it starts. The valve _H_ is then closed, which cuts the starting pump _F_ entirely out of the system, because when the engine starts it also drives the water pump _E_, and therefore the action becomes entirely automatic.

The relief-c.o.c.k _L_ is placed in the system to be used if the engine stalls. By opening the relief-c.o.c.k the pressure in the complete system is immediately relieved. At all other times the relief-c.o.c.k is closed.

A second pump, _I_, is also included in the system. This, like the water-pump, is geared to the engine and driven by it. It is the duty of this pump to convey oil from the lubricating tank _M_ into the steam feed-pipe just before it enters the steam-chest. In this way the live superheated steam carries a certain amount of lubricating oil with it in the cylinder.

Owing to the high temperature of the superheated steam, it is impossible to use bra.s.s cylinders on the steam-engines employed with flash steam systems. Steel seems to be the only cheap metal that is capable of withstanding the attack of flash steam. Bra.s.s is out of the question, since its surface will pit badly after it is in use a short time.

The boiler of a flash steam plant is covered with sheet iron so as to prevent drafts of air from deflecting the flame from the center of the boiler coils. The cover is provided with ventilators, so that the burner will not be smothered. If enough oxygen does not enter the interior of the boiler coils, poor combustion will result, and the gasolene flame will not develop its maximum heat. Upon referring again to the diagram, it will be seen that the exhaust steam pipe from the engine discharges into the stack of the boiler covering. This discharge greatly facilitates the circulation of air through the boiler coils.

After a flash steam plant has been started it will work automatically, providing all the parts are in good running order. Flash steam plants, however, are difficult to get in the proper adjustment, and once adjusted they are easily disturbed by minor causes. Owing to the fact that every square inch of surface in the flash coils is heating surface, the amount of water supplied to the boiler must be exactly what is needed. The heat must also be regulated so that the temperature of the steam will just meet the engine's needs. Many times an increase in heat causes the steam to reach such a temperature that it will burn up the lubricating oil before it reaches the cylinder of the engine. This is liable to cause trouble, because sticking is apt to occur.

Model power boats with speeds as high as thirty-five miles an hour have been made in America. Such high-speed boats must be a.s.sembled with infinite care, owing to the fact that the mechanism they carry is more or less erratic in its action, and unless it is well made results cannot be expected.

[Ill.u.s.tration: FIG. 129]

There are probably few sports more interesting than that of model power-boat racing. The Central Park Model Yacht Club of New York city is one of the most progressive clubs in America, and its members not only have a sail-boat division, but they also have a power-boat division. The members of the power-boat section have races regularly once a week, and the most lively compet.i.tion is shown. It is indeed amusing to watch these little high-speed boats dash across the pond, their bows high in the air and their little engines snorting frantically. Owing to the difficulty of keeping these small racing boats in a straight line, they are tied to a wire or heavy cord and allowed to race around a pole anch.o.r.ed in the center of the pond, as ill.u.s.trated in Fig. 129. The top of the pole should be provided with a ball-bearing arranged so that the cord to which the boat is fastened will not wind around the post. In this way the boats are caused to travel in a circle, and as the cord to which they are fastened represents the radius of the circle, the circ.u.mference can readily be found by multiplying the radius by 2, which will give the diameter. The diameter is then multiplied by 3.1416 to obtain the circ.u.mference. If the boats were permitted to travel wild they would run into the bank, a fatal procedure when they are running at high speed.

Speed boat hulls are usually of the hydroplane or sea-sled type. This type of hull is extremely easy to make. Such a hull is shown in Fig.

130. It will be seen that it has an aluminum bottom. The propeller and propeller strut will be noticed in this ill.u.s.tration.

[Ill.u.s.tration: FIG. 130]

[Ill.u.s.tration: FIG. 131]

[Ill.u.s.tration: FIG. 132]

The drawing for the particular hull shown in Fig. 130 is given in Fig.

131. First the two side pieces are cut out to the shape shown. In this particular instance the over-all length of the sides is 39-1/3 inches.

This is called a meter boat, and is built with this length to conform with the English racing rules. Next a bow piece is cut out, and this is produced from solid wood. Only two materials are used in the construction of this hull, aluminum and mahogany. Square mahogany strips are cut out and fastened inside of the side pieces by means of sh.e.l.lac and 3/8-inch bra.s.s brads. The bottom of the hull is made of 22-gage sheet aluminum. This is fastened to the square mahogany strips, since the sides of the boat are entirely too thin for this purpose. The method of fastening the strips of aluminum will be made evident by referring to Fig. 132. The aluminum bottom does not run completely over the bow piece, but merely overlaps it sufficiently to be fastened by bra.s.s brads, as ill.u.s.trated in Fig. 135. The single step in the bottom of the boat is fastened by a mahogany strip, through which the stern-tube runs and the water-scoop. The back of the boat is made up of mahogany. A small aluminum hood is bent to shape, and this is fastened to the bow of the boat and prevents the boat from s.h.i.+pping water.

In building a hull of this nature the mechanic should exercise care to see that it is in perfect balance, and that the sides are finished and varnished as smoothly as possible. This will cut down both air and water resistance. The position of the propeller strut and stern-tube will be seen by referring to the drawing of the hull in Fig. 131.

The propeller of a high-speed boat is of a high pitch and generally of the two-blade type. It should be at least 3 inches in diameter and with a pitch of about 10 inches. By this it is meant that the propeller theoretically should advance 10 inches through the water for one revolution. The rudder is generally fastened in one position, in case the boat is not used on a string and pole. It will be found advisable, however, always to run the boat in this way, and in such cases the rudder can be entirely dispensed with.

[Ill.u.s.tration: FIG. 133]

The boiler of a flash steam plant is extremely simple. Such a boiler is shown in Fig. 133. It consists merely of a coil of copper or Shelby steel tubing with an internal diameter of 1/4 inch. The boiler coils should be wound around a circular form of wood about 2-3/4 inches in diameter. In the case of copper it will not be found very difficult to do this, providing the copper is heated before being wound on the wooden form. If the copper is heated it is advisable to wind the wood with a layer of sheet asbestos before the copper tube is wound on. It is almost necessary to do this winding with a lathe, but if the mechanic does not have access to such a tool he may have to find other means of doing it, or possibly he can take it to a local machine shop and have the work done for a few cents. The boiler coil should be wound about 9 inches long.

A casing of Russian sheet iron is made to slip over the boiler, leaving sufficient s.p.a.ce between. Ventilating holes or slots are cut in the cover to permit of a free circulation of air. The boiler covering is also provided with a funnel through which the exhaust gases from the blow-lamp pa.s.s.

[Ill.u.s.tration: FIG. 134]

[Ill.u.s.tration: FIG. 135]

The blow-lamp used operates on the same principle as the ordinary blow-torch. The details of such a lamp are given in Fig. 134, and a finished torch is shown in Fig. 135. Instead of making the valves necessary for the blow-torch, it is advisable to purchase them, for they are very difficult to make accurately. The valve at the back of the torch regulates the gasolene supply that pa.s.ses through the nipple. The hole in the nipple should be about twenty thousandths of an inch. Owing to the fact that the copper coil wound about the burner is short, the tube can be filled with molten resin before it is bent. In this way the tube will not kink or lose its shape while being wound. After it is wound it is placed in the fire and the molten resin forced out with a bicycle-pump. Such a blow-torch produces a tremendous heat and throws a hot flame far up into the boiler coils.

CHAPTER XIII

SAILING YACHTS

BEFORE attempting to construct model sailing yachts the young worker should become thoroughly conversant with the different types of yachts and their fittings. In the following pages the author briefly outlines the general science of yacht-making and sailing.

Sailing yachts are made in four princ.i.p.al types. There is the cutter rig, yawl rig, sloop rig, and the ketch rig. The cutter rig is shown in Fig. 136. It consists of four sails so arranged that the top-sail may be either removed altogether or replaced by sails of smaller area. In all yachts it is necessary to haul the sails up into position by ropes known as halyards. The halyards must be led down to the deck. The model-builder, however, can dispense with much of the gear used on larger boats.

A sloop rig is ill.u.s.trated in Fig. 137. By studying the drawing the worker will see that the sloop rig differs from the cutter rig only in that she carries a single sail forward of her mast.

[Ill.u.s.tration: FIG. 137]

[Ill.u.s.tration: FIG. 136]

The yawl rig (See Fig. 138) is similar to a cutter rig, but has a small sail set up on another mast abaft the mainsail. The sheet is led aft to a spar that projects beyond the counter. The mast upon which the smaller sail is set is known as the mizzenmast. In this rig it will be seen that the main boom must be made considerably shorter than was the case in the cutter rig. This is done so that it will not follow the mizzenmast when it swings from one position to another.

[Ill.u.s.tration: FIG. 138]