In the steam engine the vapor acts alternately on each side of the piston head, but in motor boats and automobiles it acts only on one side. The speed with which this is done is amazing and the same may be said of the steam engine.
The swift rise and fall of the piston acting through the connecting rod turns the shaft directly below, which whirls the screw around at the stern. The electric spark that explodes the vapor is generated by a dry battery or by a magneto-electric machine driven by the motor itself. There is also the "make and break" spark, to which we need give no attention. The two ends of the wires in the spark plug which is screwed into the cylinder are separated by a space barely the twentieth part of an inch, across which the spark leaps, giving out an intensely hot flash.
You understand, of course, that I have given simply the principle and method of operation of the engine belonging to a motor boat. There are many parts that must operate smoothly and with the minimum of friction. Lubricating oil is as essential as gasoline; the ignition battery must be kept dry; you must know how to operate the reversing lever, to shut off, to start and to hold the desired speed. Except when racing or under some pressing necessity, the swiftest progress is rarely attained, for it is trying to all parts of the engine and consumes a good deal of fuel, which cannot be bought for a trifling price.
You would be confused by any attempt on my part to give a technical description of all the motor appliances, nor is there need to do so. If you have just bought a motor boat, you will be taught how to control and manage it by a practical instructor, and such instruction is better than pages of directions. To show the truth of what I have just said, I will quote a single paragraph from the description of the boat concerning which I shall have a good deal to say in the course of my story.
"The keel is of white oak, with specially bent elm frames. Planking of selected Laguna mahogany, finished thickness one-half inch, in narrow strakes and uniform seams, secured to frames by copper boat nails, riveted over copper washers, all fastenings being of bronze or copper to withstand salt water. Seams of hull caulked with special cotton payed and puttied. Outside of mahogany planking, finished in natural wood with spar varnish. Watertight bulkheads fore and aft which assist in floating the launch in case of accident. Decks and interior woodwork finished in selected Laguna mahogany. Steam bent quartered oak or mahogany coaming extending around cockpit."