The use of sail power as the main propulsive force for merchant vessels declined after coal, and then oil-fired propulsion, came to dominate when the range, reliability, and efficiency of these methods increased in the late 19th and early 20th centuries. However, the use of sail power to provide a proportion of power-or "wind assist"-is not new. With rapidly rising oil price in the late 1970s, there was considerable interest in, and technical development of, sail propulsion systems for merchant ships. Several hard- or wing-sail devices were deployed on bulk carriers and oil tankers, particularly of Japanese ownership. The rising oil prices sparked considerable research into the use of wind propulsion to reduce the percentage of the total power provided by the engine. Indeed, conferences on wind propulsion technology were held in the U.K.: in Liverpool in 1976, in London in 1980, and at the University of Southampton in 1985.
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