At the Sound School we try to integrate maritime topics into our curriculum, to use Long Island Sound as a theme for our teaching. Hoping that students will be motivated to greater study of a topic if they see a use for it. Here is some history of naval architecture related to aerodynamics. Aerodynamics and hydrodynamics are both part of one field called fluid mechanics. Many of the principles of fluid mechanics were known before airplanes existed. These principles had been discovered in hydrodynamics. One apparatus of investigation was the towing tank.
A. Towing Tanks
Much of the hydrodynamics was motivated by the building and maintenance of canals. In fact Benjamin Franklin built a towing tank to test the observation he had made on the canals in Holland that boats go slower in shallower water. The tank was in fact a narrow wooden trough, the model was towed by a weight falling over a pulley at one end.
Even though Ben Franklin was a founder of the United States, the U. S. Navy did not get Congress to approve funding for a tank until 1896. The tank was built at the Washington Navy Yard under the supervision of Naval Constructor David Watson Taylor who direced it for the next fifteen years. Much significant work was done.
The claims of the advocates of model testing were substantiated early on. In 1902 the Model Basin designed two armored cruisers of 14,500 ton displacement that were 820 tons heavier than similar predecessors but were able to cruise at 22 knots with less horsepower while consuming less fuel.
Taylor instituted the practice of using wooden models instead of wax models as used by other naval architects. This gave more accurate measurements, and avoided models melting in Washington, D. C. summers. It was much more expensive, however, $80 against fifty cents for wax that could be melted down and used again. He was responsible for the bulbous bow to dampen the bow wave thus decreasing wave resistance. This type of bow was first used on the USS
in 1907 with great success.
The technological “giant steps” of any historical period determine the topics of scientific research for that period. The
was one such giant step.
Construction of the
started in 1854, her launching began in November, 1857, and she finally floated at the end of January, 1858. She was 680 feet long the next longest ship of her day was 380 feet. Her length was not exceeded until the
in 1899 and her tonage was not exceeded until the
in 1906. The reason it took three months to launch her was that metal rails where used for the ways and the cradles were iron shod. So much heat was generated by the friction of iron against iron that the cradle shoes and the rails welded themselves together in November at the first attempt. The ship was jacked down the ways an inch at a time after jacks were designed and built.
She was the only vessel ever built that had sails, paddle wheels and propellers, with the paddle wheels and propellers having their own independent engines. She burned a ton of coal per mile. She had a capacity of 12,000 tons of coal. She was under powered, she had about 2600 horsepower with a top speed of 14.5 knots on a displacement of 27,000 tons. Remember, no one had ever done this before, there were bound to be mistakes, and unforseen problems. All her problems pointed out the need for even more scientific investigations. Her builders had been successful in their previous ventures building other ships, rail roads and bridges.
One engineer associated with the
was William Froude. From his experiences grew his life’s work the study of the powering of ships. Other names to research are J. Scott Russel who designed her and built her in his ship yard. The name that most people associate with the
is Isambard Kingdom Brunel the owners, technical advisor and probably the top engineer of the time. It is a question of historical research as to how much Brunel contributed to the design, it is called “Brunel’s great ship” and its misfortunes are said to have killed him.
One succes of the
was the laying of the transatlantic telegraph cable after the Civil War. To learn more see the article by Chiles in the Fall l987 issue of
Invention & Technology
In search of more speed more efficient engines were built and placed in ships. The first turbine powered ship was Sir Charles Parsons’
built in l894. Parsons had built the first successful turbine to power a dynamo, an electric generator. He had done model tests and had great expectations for the ship, the turbine was very powerful.
The results were disapointing. The higest speed recorded was less than 20 knots. The problem was cavitation, a phenomenon recognized and named by William Froude. The propellers were spinning at l8,000 rpm, as they spun they decreased the pressure until the water became vapor, a bubble, a cavity. The power was going into making the bubble instead of pushing the boat.
The remedy was to operate at lower rpm with more turbines and propellers. The original design was one turbine with one shaft of three propellers. The successful design was three turbines each having a shaft turning three propellers, which achieved the speed of 34.5 knots in 1897.