The advantages of the motor are so great that the Scotch authorities have taken the matter up seriously, appointing an expert to make inquiries. It is therefore quite possible that before many years have elapsed the motor will play an important part in the task of supplying our breakfast tables with the dainty sole or toothsome herring.
A MOTOR FIRE FLOAT
As a good instance of this particular adaptation of the explosion engine to fire-extinction work, we may quote the apparatus now in attendance on the huge factory of Messrs. Huntley and Palmer, the famous Reading biscuit makers. The factory lies along the banks of the river Kennet, which are joined by bridges so close to the water that a steamer could not pass under them. Messrs. Merryweather accordingly built the motor float, 32 feet long, 9 1 / 2 feet beam, and drawing 27 inches. Two engines, each having four cylinders of a total of 30 h.p., drive two sets of three-cylinder "Hatfield" pumps, which give a continuous feed to the hose. Engines and pumps are mounted on a single bed-plate, and are worked separately, unless it be found advisable to "Siamese" the hoses to feed a single 1 1 / 2 -inch jet, which can be flung to a great height.
One of the most interesting features of the float is the method of propulsion. As its movements are limited to a few hundred yards, the fitting of a screw was considered unnecessary, its place being taken by four jets, two at each end, through which water is forced against the outside water by the extinguishing pumps. These will move the float either forward or astern, steer her, or turn her round.
So here once again petrol has trodden upon the toes of Giant Steam: and very effectively, too.
THE MECHANISM OF THE MOTOR BOAT
In many points the marine motor reproduces the machinery built into cars. The valve arrangements, governors, design of cylinders and water-jackets are practically the same. Small boats carry one cylinder or perhaps two, just as a small car is content with the same number; but a racing or heavy boat employs four, six, and, in one case at least, twelve cylinders, which abolish all "dead points" and enable the screw to work very slowly without engine vibration, as the drive is continuous.
The large marine motor is designed to run at a slower rate than the land motor, and its cylinders are, therefore, of greater size. Some of the cylinders exhibited in the Automobile Show at the London "Olympia" seemed enormous when compared with those doing duty on even high-powered cars; being more suggestive of the parts of an electric lighting plant than of a machine which has to be tucked away in a boat.
Except for the reversing gear, gearing is generally absent on the motor boat. The chauffeur has not to keep changing his speed lever from one notch to another according to the nature of the country. On the sea conditions are more consistently favourable or unfavourable, and, as in a steamboat, speed is controlled by opening or closing the throttle. The screw will always be turned by the machinery, but its effect on the boat must depend on its size and the forces acting in opposition to it. Since water is yielding, it does not offer a parallel to the road. Should a car meet a hill too steep for its climbing powers, the engines must come to rest. The wheel does not slip on the road, and so long as there is sufficient power it will force the car up the severest incline; as soon as the power proves too small for the task in hand the car "lies down." In a motor boat, however, the engine may keep the screw moving without doing more against wind and tide than prevent the boat from "advancing backwards." The only way to make the boat efficient to meet all possible conditions would be to increase the size or alter the pitch of the screw, and to install more powerful engines. "Gearing down"—as in a motor-car—being useless, the only mechanism needed on a motor boat in connection with the transmission of power from cylinders to screw is the reversing gear.
Though engines have been designed with devices for reversing by means of the cams operating the valves, the reversal of the screw's movement is generally effected through gears on the transmission apparatus. The simplest arrangement, though not the most perfect mechanically, is a reversible screw, the blades of which can be made to feather this way or that by the movement of a lever. Sometimes two screws are employed, with opposite twists, the one doing duty while the other revolves idly. But for fast and heavy boats a single solid screw with immovable blades is undoubtedly preferable; its reversal being effected by means of friction clutches. The inelasticity of the explosion motor renders it necessary that the change be made gradually, or the kick of the screw against the motor might cause breakages. The clutch, gradually engaging with a disc revolved by the propeller shaft, first stops the antagonistic motion, and then converts it into similar motion. Many devices have been invented to bring this about, but as a description of them would not be interesting, we pass on to a consideration of the fuel used in the motor boat.