MOTOR BOATS, power boats equipped with internal-combustion engines, as distin guished from boats propelled by steam power. They divide into several groups or types: (1) or sets of engines varying from 50 to 300 or more horse power.
The hulls are built in several styles round-bottom, flat-bottom, V-'bottom, tunnel bottom, etc., and with widely varying types of bow and stern. Of the former, the prevailing types are the straight, round, dory, spoon and clipper bows; of the latter, the square, round, transom, fantail and torpedo sterns. A straight bow has the most elegant appearance, but a round bow rides better and is preferable. A transom or V-shaped stern makes the fastest and driest boat. Open boats of the launch class have a few feet of deck forward and aft, with a narrow strip along the gunwales, and a five or six-inch coaming around the cockpit. They are often fitted with a spray shield of canvas or a °.buggy-top" sun and rain shield. Larger boats are protected by an awning top carried on a frame overhead, or by a fixed °standing roof)) which is commonly fitted with side cur tains of canvas, making a weather-tight in closure, but dangerous in a high wind. Boats 25 to 30 (or more) feet in length usually have a cabin of some sort. This may be of the °raised or °hunting cabin)) type, inclosing the bow for several feet back, or a °glass cabin)) inclosure toward the middle of the hull. The last is liable to make the boat top-heavy unless it has considerable width of beam.
At the Paris Exposition of 1889 there was exhibited a boat with a Daimler motor, this being among the first of the motor boats. As this form of motor was developed and im proved for automobiles and aeroplanes, manu the gasoline launch, commonly 20 to 30 feet long; (2) speed boats, sometimes called dis placement speed boats, more or less decked over and with high-powered engines: they often run up to 40 feet in length; (3) hydroplane boats, having stepped planes in the hull and designed to slide on the water rather than through it; (4) cruisers, virtually pleasure yachts, using gasoline motor engines instead of steam engines and usually built with a view to speed. These last are commonly 60 to 100 or more feet in length, and they carry engines facturers adapted it to boats, and the internal combustion or gasoline engines built for motor boats are quite as efficient as those constructed for automobiles and motor vehicles. Not hav ing the same weight restrictions, they are usually of heavier construction, and they are built up to large sizes. As arranged for motor boats, the internal-combustion engine is simpler than for automobiles. No radiator is required
to cool the cylinders, the water-jacket of the cylinders being supplied by a continual current of fresh water taken in from beneath the hull; and no change-gear for various speeds nor differentials are needed. The engine may be direct-connected to the propeller-shaft. Motors of two to six cylinders are in common use. In small boats the gasoline or fuel tank is placed forward to get it high enough to feed the car buretter by gravity. The exhaust is carried to a water-cooled muffler and thence outboard. The crank-shaft is run fore and aft and is coupled to the propeller shaft. The latter has thrust-bearings with steel balls to relieve the friction. The propellers are made with two or three blades and special forms of spiral blades are made for shallow and weedy water. Some 20-foot motor boats are made to run in one foot of water, the propeller being placed in a tunnel in the hull. Some propellers have adjustable blades, which can be positioned so as to rotate either right-hand or left-hand, though the driving is in one direction. This adjustment therefore fits the boat for either forward or backward motion. The more common method, however, is to have the propeller-shaft geared to the engine by a lever-operated reversing gear.
A familiar type of six-cylinder internal combustion engine for motor boats is shown, in the diagram. The cylinders are cast in pairs and placed upright, as in an automobile, with the two-cylinder two-cycle motor having the same effective power as the four-cylinder four cycle motor. For the ordinary motor boat no engine is better than the three-cylinder two cycle motor. It runs with a minimum of vibra tion, and is of less dead weight for the power developed than any other. The ignition system is another fundamental feature upon which the motor boat operators and builders divide in opinion. The two systems in use are the make and-break, and the jump-spark systems. Few who have had a serious amount of experience with both will hesitate to choose the make and-break as the easiest to get along with in all circumstances. Most motor builders recognize this condition, and nearly every make of motor may be had with either system. Cabin motor boats, as a rule, are equipped with a storage battery, and a generator attached to the pro peller shaft to keep it charged, thus providing the boat with a lighting system, and affording current for a searchlight to aid the pilot in making landings after dark.