A very suitable method of mounting an electric motor is ill.u.s.trated in Figs. 44 and 45. It will be noticed that the motor is inverted. A small pinion or gear is mounted upon the armature-shaft of the motor. A larger gear (about three times the diameter of the small one) is placed upon the propeller-shaft. This gives a speed reduction of three to one. It will be seen that the propeller-tube is strapped within a strip of bra.s.s to a small cross-piece nailed to the bottom board of the hull. The hull is of the built-up type, and the other three boards that go to make it up are not shown. When the three boards are glued in place, a bra.s.s strip is run across the top board and the base of the motor is screwed to this. This holds the motor rigidly in place so that it will not move when the power is turned on. The bra.s.s strip used should have sufficient thickness to hold the motor rigid. It will also be seen that the motor is tipped slightly so that it will come in line with the propeller-shaft.

[Ill.u.s.tration: FIG. 46]

[Ill.u.s.tration: FIG. 47]

[Ill.u.s.tration: FIG. 48]

It is not always possible to obtain small gears. For this reason the model boat builder may find it necessary to use a different method of fastening the propeller-shaft to the motor. A very good method of doing this is shown in Fig. 46. Here a coiled wire spring is used. This is wound to shape on a rod, and a drop of solder holds it to the propeller and motor shafts. In the method of propulsion shown in Fig. 44 the armature-shaft of the motor must be perfectly in line with the propeller-shaft, or the gears will bind and unsatisfactory operation of the motor will result. With the little spring the motor will not have to be mounted exactly in line with the shaft, and it will also be possible to mount the motor standing up. Of course, if the motor is mounted in this way it will be necessary to make the propeller-shaft longer, as is shown in Fig. 47.

Still another method of driving the propeller is ill.u.s.trated 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.

[Ill.u.s.tration: FIG. 49]

[Ill.u.s.tration: FIG. 50]

[Ill.u.s.tration: FIG. 51]

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 a.s.sembling the boiler is pictured clearly in Fig. 49. A bra.s.s 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 bra.s.s 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 bra.s.s 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 bra.s.s 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.

[Ill.u.s.tration: FIG. 52]

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 ill.u.s.trated 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 ill.u.s.trated. A piece of bra.s.s 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.

[Ill.u.s.tration: FIG. 53]

[Ill.u.s.tration: FIG. 54]

The engine to be used in connection with the boiler just described is shown in Fig. 53. This is a very simple engine of the oscillation type, and there should be little trouble in making it. A more mechanical drawing of the engine is shown in Fig. 54. The details of the engine are shown in Fig. 55.

[Ill.u.s.tration: FIG. 55]

The cylinder of the engine should be made first. This is made from a piece of bra.s.s tubing with an internal diameter of 3/4 inch. Two end pieces, or a cylinder-end cover and cylinder head, must be cut to fit inside the cylinder. These should be cut to shape from 1/16 inch bra.s.s, and a hole drilled in the cylinder head 1/8 inch in diameter to accommodate the piston-rod. The cylinder head is then soldered in place.

The cylinder-end cover should be left until the piston-rod and piston are made.

The piston head is cut to shape from a piece of 3/16-inch sheet bra.s.s, or it can be cut from a piece of 3/4-inch round bra.s.s with a hacksaw.

The piston-rod is soldered into a hole in the piston-head. A small square piece of bra.s.s is placed on the opposite end of the piston-rod to act as a bearing. This little piece is cut and drilled as shown in the drawing. Before it is soldered in place on the piston-rod the cylinder-end cover should be placed on the rod. Both the piston and the cylinder-end cover can then be placed inside the cylinder, and the piston-end cover is soldered in place. Before final a.s.sembling the piston should be made to fit nicely into the cylinder. This can be brought about by applying emery cloth to the piston-head until it slips nicely into the cylinder with little or no play. Thus a steam-tight fit is made, and this contributes greatly to the efficiency and power of the engine.

[Ill.u.s.tration: FIG. 56]

[Ill.u.s.tration: FIG. 57]

The cylinder blocks are shown in Fig. 55. These are cut and brought to shape with a hacksaw and file. With a half-round file one side of one of the blocks is filed slightly concave, so that it will fit on the outside of the cylinder. Two 1/8-inch holes are drilled in this piece as shown in the drawing. The hole at the top is the steam entrance and exhaust for the engine; that is, when the cylinder is at one side steam enters this hole, and when the crank throws the cylinder over to the other side steam leaves through the same hole after having expanded in the cylinder. This cylinder block is soldered to the piston as shown in Fig. 56. The pivot upon which the cylinder swings is then put in place in the hole at the bottom of the block. Solder is flowed around the pivot to hold it securely in place.

The second cylinder block is now finished according to the drawing. This has two holes 1/8 inch in diameter bored in it. One of these holes is the steam inlet and the other the exhaust. When the cylinder is at one side of its stroke the hole that was bored in the top of the steam block which was soldered on the cylinder is in line with the inlet hole in the block under consideration. Steam then enters the cylinder and forces the piston down. This turns the crank around, and the crank in turn pulls the piston over to the opposite side, so that the hole in the first piston block of the cylinder now comes in line with the exhaust hole on the second cylinder block. The steam in the cylinder escapes and the same operation is repeated over again. Of course, it must be understood that this steam admission and exhaust takes place very rapidly. The hole in the second cylinder block, which goes over the pivot, must be made a trifle more than 1/8 inch in diameter, so that it will slide freely over the pivot.

The engine is mounted on a very simple frame, which is a piece of 1/16-inch bra.s.s cut and bent as ill.u.s.trated. After it is cut and bent to shape the second cylinder block is soldered in place. The cylinder can then be mounted. It will be seen that the pivot goes through both the second cylinder block and the engine standard. A small spring is placed over the protruding end of the pivot and a nut put in place. By turning this nut the pressure on the face of the two cylinder blocks can be adjusted, and the model engineer must always remember that the pressure on these springs must be greater than the steam pressure in the feed-pipe. Otherwise the steam pressure will force the cylinder-block faces apart and steam leakage will result. On the other hand, the pressure of the spring should not be too great, since that would interfere with the free movement of the engine cylinder.

Nothing now remains to be made except the crank and the flywheel. The crank revolves in a small bra.s.s bearing which is soldered in place on the engine standard. It will be seen that the sheet bra.s.s that makes up the engine standard is not thick enough to offer a good bearing for the crank. The crank is bent to shape from a piece of 1/8-inch bra.s.s rod, and the author advises the builder to heat the bra.s.s rod red-hot while the bending is done. This will prevent it from fracturing, and will also permit a sharp bend to be made.

The flywheel is a circular piece of bra.s.s 1 inch in diameter. Its center is drilled out and it is soldered to the crank as ill.u.s.trated in Fig.

54. Two other holes 1/8 inch in diameter are drilled in the flywheel as ill.u.s.trated, and two small bra.s.s pins are cut out from 1/8-inch bra.s.s rod and forced into these holes and then soldered. These provide a method of driving the propeller-shaft that is shown very clearly at Fig.

57.

The steam feed-pipe that runs from the boiler to the engine can be of small copper tubing. It may be necessary to mount the engine on a small block, as shown in Fig. 53. After the steam in the boiler has reached a sufficient pressure the engine crank should be given a couple of twists in order to start it. Before operating the engine a little lubricating oil should be run into the cylinder through the inlet or exhaust ports.

The cylinder should always be kept well lubricated. The contacting faces of the cylinder blocks should also be kept lubricated.

_Caution._ Always keep water in the boiler. Never permit it to run dry, as this would cause a boiler explosion. When the engine is started and cannot be made to run, take the burner from under the boiler so that steam will cease to be generated. With the safety-valve the model boat builder need have little fear of an explosion. Nevertheless the foregoing directions should be carefully adhered to.

CHAPTER V

AN ELECTRIC LAUNCH

THE little electric launch to be described is of very simple construction, and when finished it will provide the builder with a very shipshape little model from which he will be able to derive a good deal of pleasure. It has a speed of from 2-1/2 to 3 miles an hour when equipped with dry batteries or storage batteries. The hull is of the Sharpie type, and this offers very little trouble in cutting out and a.s.sembling.

The general appearance of the boat and hull will be gathered from the drawings. The pieces necessary to a.s.semble the hull are shown in Fig.

58. Only five pieces are necessary: two side pieces, a stern piece, a bow piece, and a bottom piece. The length of the boat over all is 40 inches with a 7-inch beam. The widest part of the boat is 1 foot 10 inches from the bow.

After the pieces that form the hull are cut they are thoroughly sandpapered to produce a smooth surface. The heavy imperfections in the wood can be taken out with coa.r.s.e paper, and the finishing can be done with a finer paper. It is understood that sandpapering should always be done with the grain, never across the grain. The sides of the boat are cut about 1/4 inch thick, but they are planed thinner in places where the bend is most p.r.o.nounced. The side pieces are 2-3/4 inches deep at the stern and 2-1/4 inches at the stern. There is a gradual curve from the bow to the stern, which is more marked toward the head.

The stern piece is thicker than the side pieces, being made of 1/2-inch wood. It is cut to the shape shown at Fig. 58, and beveled along the bottom edge to enable it to be fixed on the slant. The bow piece is a triangle 2-3/4 inches in length.

After the parts are thoroughly finished with sandpaper the stern piece is fixed in position. In making all the joints on the boat the builder should see that plenty of fairly thick paint is run in while the joint is being screwed up. This will help greatly in making the boat water-tight. Plenty of 3/4-inch bra.s.s wood-screws are used in a.s.sembling the hull. All the holes for the wood-screws should be countersunk so that the heads will come flush with the surface of the hull. Now one of the sides should be screwed to the stern piece, at the same time bending the bottom and side to meet. This is done gradually, inch by inch, and screws are put in place at equal distances. When the bow is reached, the side piece is beveled to fit the bow piece, which should already have been screwed into place. The other side of the boat is treated in a similar manner, and the young worker should take care to keep the side and bow piece perfectly square and upright. This may sound easy on paper, but it will be found that a good deal of care must be exercised to produce this result.

After the hull has been a.s.sembled it is given a good coat of paint inside and out. When the first coat is dry the holes left by the screw-heads are carefully puttied over, and the hull is given a second coat of paint. This procedure will produce a perfectly water-tight hull.

[Ill.u.s.tration: FIG. 58]

[Ill.u.s.tration: FIG. 59]

[Ill.u.s.tration: FIG. 63]

The stern tube is 3/8 inch, outside diameter. A hole is bored in the bottom of the boat to receive the stern tube. This job must be done cautiously; otherwise the bottom of the boat may be ruined. It is best to screw a substantial block to the inside of the boat. This block should be cut to fit the bottom and will act as a support for drilling.

It will also help greatly to make a water-tight joint around the tube.

The distance from the point where the stern tube pa.s.ses through the bottom to the stern should be about 12-1/2 inches. The stern tube should be mounted as nearly parallel with the bottom as possible, since on this depends the speed of the boat. As the angle of the propeller-shaft increases, the speed of the boat will decrease. In drilling the hole the boat-builder should be careful to keep the drill running along the central line of the boat.

As before mentioned, the stern tube is a piece of bra.s.s tubing 3/8 inch in diameter and 8 inches long. It is filed square at both ends, and a bra.s.s plug is fastened with solder in each end. The tube is then filled with melted vaseline, which is allowed to cool. The hole in the hull around the tube is then well smeared with thick paint. When this is done, a layer of red lead or putty is placed around the joint both on the inside and the outside of the boat.