Motorboats are water craft smaller than those ordinarily used as cargo ships, and propelled by internal-combustion engines (sometimes by jet engines).
During the 1880's, when the weight of engines in steam launches seemed to bar further development of small power boats, a number of builders in England, France, Germany, and the United States experimented with internal-combustion engines. J. J. R. Hulme of London propelled a launch with gasoline in 1885, and a boat with an engine designed by the German Gottlieb Daimler was launched in 1886. In 1902, attempting greater speed on water, the Englishman Selwyn Francis Edge attained 19 knots with a 66-horsepower engine.
Between the turn of the century and World War I many new types of hull appeared. Designers found that if they could raise the hull partially into the air by the forward propulsion of the boat, the resistance of the water would be decreased. This discovery led to the development of the hydroplane, a boat whose hull shape, coupled with its relationship of power to weight, causes the bow to rise out of the water as the boat gathers speed. Rather than driving through the water, the hull planes over the surface. V-bottoms, round bottoms, catamarans, sea sleds, and a number of designs utilizing washboard bottoms were all tried during this period. The English naval architect Sir John Thornycroft's "skimming boat" Tadpole (1909) carried a web under the bow with a heart-shaped plane that lifted the bow from the water. Between 1898 and 1905, the Italian Enrico Forlanini equipped a boat with "ladder foils," and in 1907, Wilbur and Orville Wright experimented with a hydrofoil catamaran.
Marine engines have never been different in principle from internal-combustion engines for automobiles and other purposes. Except for the later air-cooled and outboard motors, they have tended to be of heavier construction, and have taken in water from beneath the hull for cooling, instead of from radiators.
Since the early 1900's, motorboat racers have pioneered in better engines and in new designs for hulls. In 1903 international competition was first organized when the British newspaper owner Sir Edward Harms-worth offered a cup which has since been called the Harmsworth or British International Trophy. From 1920 to 1956 this trophy was won by boats from the United States The American Power Boat Association's Gold Cup, first offered in 1904, is a coveted American trophy. World speed records are not set in the Harmsworth and American Gold Cup races because both are held on courses with bends that test the maneuverability of boats and skill of drivers as well as speed.
Under the rules of the Union of International Motor Boating, a world record may be set by making two runs of a measured mile and taking the average speed of both.
In 1939, Sir Malcolm Campbell's Bluebird II was timed at 141.74 mph. (miles per hour) and established a record that stood for 11 years. The hull of this boat incorporated the three-point (Apel) design, planing on two forward surfaces placed athwartship and a small area at the stern. After World War II, Campbell installed a De Haviland Goblin II jet engine, but found that his craft could not be held on course until full power was developed. In adapting motorboats to jet engines, designers faced a host of new technical problems.
The official world speed record continued to be held by a boat driven by a gasoline engine. Campbell's record was broken in 1950 when 570-Mo-Shun IV, designed by Ted Jones and owned by Stanley Sayres of Seattle, Wash., went 160.3235 mph. In 1952, Slo-Mo-Shun IV broke its own record by going 178.497 mph. This craft was designed to avoid cavitation, which is a barrier to the development of greater speeds in propeller-driven craft; this condition occurs when the propellers turn faster than the water can close in on them, so that a partial vacuum is created. Consequently, at high speeds the propeller loses efficiency. Jones' record was surpassed in 1962 by Roy Duby, who drove his hydroplane at a speed of slightly over 200 mph. in a straightaway run of one mile.
Jet-propelled hydroplanes now hold the world's speed records on water. On Loch Ness in 1952 the English sportsman John Cobb was killed just after his jet-driven Crusader went 206.89 mph. for one measured mile. After completing this first run, his boat dove to the side and disintegrated. Although Cobb's one run did not constitute an official world's record, he had attained the fastest speed yet recorded on water. Donald Campbell, driving his turbojet hydroplane, Bluebird, set official world's records of 202.35 mph. in July 1955 and 216.02 mph. in November 1955. Later he broke his records again and again. He attained a speed of 276.33 mph. on Lake Dumble-yung in Australia in 1964.
To put motorboat racing economically within the reach of more people, the American Power Boat Association and similar organizations in other countries have drawn up rules defining various classes for competition. Motorboat racing is a thrilling and sometimes dangerous sport, with the light boats bucking wildly in each other's wakes. Spills at high speeds are not uncommon, and the rules in many classes require contestants to wear helmets and life preservers.
Classes come under the general classifications of inboard, outboard, displacement, and hydroplane, and are determined primarily by the engine's piston displacement. The size, cost, and type of hull also are often specified. There are over 35 classes in active competition in the United States. Motor and hull in the tiniest classes may cost under $1,000 while unlimited hydroplanes competing for the Gold Cup may cost $25,000 up.
During World War I the English designer Sir John Thornycroft invented a mono-step hull for a motor torpedo boat which was found to be faster than either a V-bottom or inverted V-bottom. The motor torpedo boat became technically the most advanced craft powered by internal combustion.
In World War II all the major naval powers had complements of motor torpedo boats, air-sea rescue boats, patrol boats, motor gunboats, and a variety of motor launches and lifeboats. Both Great Britain and the United States developed motor lifeboats that could be dropped into the sea for wrecked airmen. In addition, the United States Coast Guard had a large number of patrol boats, those over 56 feet long rated as cutters, and two types of 38 and 40 feet in length rated as pickets.
After World War II, France, Great Britain, Sweden, the Soviet Union, and the United States all produced motor torpedo boats that are undoubtedly the most powerful motorboats ever built. Most of these craft range between 60 and 100 feet in length, develop from 3,000 to 10,000 horsepower, and are capable of speeds from 35 to upward of 40 knots. They may be equipped with torpedo-launching devices, rocket projectors, small cannon, machine guns, and antiaircraft weapons. A typical American model was characterized in the pages of Jane's Fighting Ships as having "greater displacement, range, fire power and stability" than the World War II PT boats. Unlike the PT boats, built of plywood, the newer motor torpedo boats are built of aluminum.
The tactical usefulness of motor torpedo boats (MTB's) was demonstrated during the Battle of Britain in World War II. According to some naval authorities, the MTB's played a role comparable to that of the Royal Air Force in preventing invasion. The British Admiralty's summary of the war record of small motor craft states that motor torpedo boats, gunboats, and launches fought 782 actions, sank, damaged, or captured more than 500 enemy ships, and lost 176. Great Britain began World War II with 21 motor torpedo boats and ended it with 1,550.
During World War II an improved hydrofoil was developed. In this design, a stilt holds the planing surfaces under the boat so that the forward propulsion of the craft raises the hull completely out of the water. Since the resistance of the hydrofoils is not nearly so great as that of the hull, some designers expect to develop great speeds in hydrofoil craft. A number of civilian hydrofoil boats have been developed to carry passengers locally at very high speeds. Navies are continuing to produce new designs.
Motorboating for Pleasure
After World War II, pleasure boating became a more popular recreation in the United States than it had ever been. By the mid-1960's, there were about 5 million motorboats of various types in the United States for the purpose of recreation. Something like 20 million Americans participated in motor-boating ; these people spent millions of dollars annually on the sport. It is true that nonmotor-ized boats, such as sailboats and rowboats, were also popular; but they were outnumbered by motorboats.
Most of the latter type of craft were out-boards; the inboards came to less than a million. The vast increase over the years in the number and uses of motorboats was due primarily to the development of light, efficient, and relatively cheap motors, with numerous refinements making them easier to operate and to control. Plywood, aluminum, and glass fiber hulls were replacing steel and wooden types.