almost totally rebuilt and re-rigged using modern materials, to enable them to race today. Originally, these vessels did not have the niceties of the modern winches and required up to 19 men hauling on a sheet to tighten home a headsail in heavy wind. Te latest America’s Cup vessels are trimarans built to the most advanced technology in hull and rig design, but perhaps lacking the grace and potential future use as their J Class predecessors. During the early 20th century, offshore races evolved, including


the Bermuda race in 1906 and Fastnet race in 1925. USA designs oſten won the trophies, particularly during 1950s, with the advent of more sophisticated tank testing. Tis was utilised with great success by the yacht designers Sparkman and Stephens. In the 19th century, American yachts such as the America were very successful due to the use of cotton in the manufacture of sails, rather than the heavier flax canvas. Sail development today has been one of the major factors in the increase in sailing yacht performance with combinations of plastics, mylar, kevlar and carbon fibre, allowing the very high precision cut and developed sail shapes, resulting in high speeds and ability to sail close to the wind. Monohull forms have developed from the long keel fine ended


sailing fishing boats and pilot boats of the 18th and 19th centuries to the more extreme canoe bodied deep fin keel hull forms with a ballast keel bulb, developed in the mid 20th century for model yacht racing, again demonstrating the benefit model design and tank testing to the development of hull forms. But probably, the most exciting development in sailing vessel design has been the introduction of multi hulls – catamarans and trimarans of very light weight, largely achieved by the use of carbon fibre and epoxy resin construction with large rigs of highly controllable material. Tese vessels have reached speeds which were unimaginable at the turn of the 20th century. In excess of 40 knots is oſten attained, and the current round the world record at just over 50 days, with an average speed of 22 knots, is held by Orange II.


hull forms to “bend or cheat” the Rule. In 1887 the Tames Rule was introduced giving a rating based on the formula LxBxB/2÷ 94. Tus breadth, being a squared term, has a very significant effect on the rating. In this case, half breadth was intended to represent the depth of the hull, breadth being easier to measure than depth. Vessels became narrower and deeper, resulting in the extreme 5 tonne Oona, drawing eight feet but only having 5.5ſt beam. Today, racing Rules are far more sophisticated and try to


control extremes. However, this has encouraged “one design” yacht racing, enabling yachtsmen to race on supposedly equal terms as far as the vessel is concerned. However, “one design” racing, adds little to progress in naval architecture, or the development of structures. The development of speed in motor vessels reached a


peak with steam powered propellerdriven torpedo boats and destroyers, achieving 30 knots in the late 1890s. Parsons Engineering Company developed the fast steam turbine launch Turbinia to show the advantage of this form of propulsion, the vessel powering at speed between the massive warships at the Spithead naval review in front of Queen Victoria to publicise turbine propulsion. Petrol and diesel engines were developed in the 1890s and


gave the advantage of the fuel being carried in tanks, rather than coal holds, where the boiler fire required continual manual stoking. Hull development progressed quickly during the early 1900s with the stepped bottom being shown to dramatically reduce wetted surfaces for high-speed planning vessels. John I Thornicroft & Co. developed a vessel capable of 55 knots, a remarkable achievement in view of the poor power to weight ratio of the engines compared with the modern internal combustion engine. Smaller high-speed motor yachts were built during the 1920’s


with Hubert Scott Payne developing the ancestor of the more modern 30 knot motor yacht. Other high-speed motor yacht builders, in particular Isotta Fraschini, Hall Scott, Packard and Sterling, used lightweight petrol engines, while the high speed lightweight diesel was developed in Germany. In 1912, Maple Leaf IV, built by S E Saunders with a 40ſt waterline length, achieved 50 knots with two petrol engines of 800 horsepower. Tis compares well with modern motor yachts of that size where speeds in the larger power boat classes reach 100 knots. Probably, the two greatest changes in the development of


America


In sailing yacht racing, the introduction of a racing Rule to which the vessel should be built has always resulted in extreme


80


motor yachts since 1860 have been in construction materials and screw propulsion. Fast vessels, both power and sail, were largely built of laminated timber when bone glues became sufficiently strong with closely framed and stringered hull shells. Today, the most sophisticated vessels are built of carbon fibre and epoxy resin, usually in sandwich construction, using very thin skins of laminate separated with a plastic foam core. Tis results in a structure many times stronger and stiffer than the best timber construction of the early 20th century. Problems were experienced with traditional propeller screw


propulsion with speeds exceeding 35 knots, where cavitation became increasingly damaging to the propeller blades. Tis did not matter much for relatively short races but for high-speed


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