Model power boats with speeds as high as thirty-five miles an hour have been made in America. Such high-speed boats must be assembled 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.
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 competition 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 anchored in the center of the pond, as illustrated 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 circumference 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 circumference. 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 illustration.
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 391/3 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 shellac and 3/8-inch brass 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 brass brads, as illustrated 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 shipping 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.