THE MOTOR BOAT GASOLINE ENGINE Gasoline engines for motor boats are of the two and four cycle types and are made with one, two, four, six and eight cylinders.
The Fuel Feed System Again.—The gravity feed, the air pressure feed, and the vacuum, feed systems of fuel supply are all used on motor boat engines, and these are identical with those used on motor car en gines.
In small boats, the gasoline tank is often made to fit in the bow of the boat, and as this is higher than the carburetor the gasoline flows down by gravity. Where a larger supply of fuel is wanted a cylindrical pressed steel tank can be mounted on the boat back of the seat just as it is on a runabout car.
The regular float valve carburetor is used on motor boat engines, and the speed of the engine is controlled by a throttle, that is, by a lever which opens and closes the throttle valve. On large engines the fly ball type of governor is used, and by means of it any speed desired can be kept up.
Electric Ignition Systems.—There are three kinds of igniters used for firing the fuel charge of motor boat engines, and these are (1) the make and break, (2) the jump-spark coil, and (3) the magneto sys tem.
The make and break scheme of ignition is used on single cylinder engines. Where a make and break coil is used the timer is worked by an eccentric on the camshaft. It is preferred to a high tension sys tem, as it is not as easily short-circuited by water.
The jump-spark coil system is practically obsolete on motor boat engines, the more positive and less troublesome magneto having all but superseded it.
The Oiling Systems.—On small engines grease and oil cups are used to lubricate the piston and crankshaft. These cups have been described and pic tured in Chapter III. The larger engines are oiled by the splash and force feed systems, as explained under the heading of Motorcycle and Motor Car Gasoline Engines.
The Engine Cooling System.—Since a constant supply of cold water is always at hand for cooling a motor boat engine a radiator is not needed. The water is pumped from that on which the boat rides, through an intake pipe that connects the supply with the jacketed cylinders, and it flows out of the latter back to the supply by an outlet pipe.
Kinds of Pumps are three kinds of pumps used on motor boat engines, and these are (1) the ordinary piston, or plunger pump; (2) the centrifugal pump, and (3) the gear pump.
Where a plunger pump is used it is driven by an eccentric on the camshaft just as it is when used for pumping gasoline as shown in Fig. 88. Centri fugal and gear pumps are also used in water cir culating systems.
The Exhaust Pipe and exhaust pipe of the engine gets red-hot, nearly, and to keep it from burning the boat where it goes through it must be jacketed, that is, it must be enclosed in another pipe and be cooled by water circulating between them. The exhaust is made on the same principle as that of a motor car engine.