Jorge Juan y Santacilia , a Spanish mathematician, scientist, naval officer, and mariner. He determined that the Earth is not perfectly spherical but is oblate.

Last night watched an interesting documentary on The Incredible Discovery Of An 18th Century Warship -  Triunfante.  The Triunfante was launched in 1756 and foundered thirty-nine years later in 1795.  She was caught in a bay during a storm.  When she was unable to weather the headland to reach open sea, her captain put about and ran her aground within a hundred feet of shore.  No loss of life and most materials were removed the next day but she was unable to be refloated and was abandoned.

I have always had the impression of the Spanish Navy in this period being hide-bound and of relatively weak quality.  The documentary introduced me to Age of Enlightenment scion, Jorge Juan, a gifted polymath who sought to reform the Spanish Navy by redesigning Spanish ships incorporating techniques and technologies from the most advanced ship-builders of the time, Britain and France.  

In the excavation of the Triunfante, they were able to document some of these design changes but also produced evidence of how slowly institutions change.  Though the ship was designed as a hybrid between Spanish and British techniques, the forty years of maintenance were all traditional Spanish.

The Wikipedia entry on Jorge Juan:

Jorge Juan y Santacilia (Novelda, Alicante, 5 January 1713 – Madrid, 21 June 1773) was a Spanish mathematician, scientist, naval officer, and mariner. He determined that the Earth is not perfectly spherical but is oblate, i.e. flattened at the poles. Juan also successfully measured the heights of the mountains of the Andes using a barometer.

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His father died when Juan was only three years old and he grew under the care of the Jesuits of the Jesuit school in Alicante. His uncle don Antonio Juan, a Canon at the Collegiate Church took charge of young Jorge and continued his education. Later another uncle, don Cipriano Juan, a Knight of the Order of Malta, took charge of his education and sent him to Zaragoza for a preparatory education for higher studies.

At the age of 12, he was sent to Malta to receive Holy Orders at the Order of Malta. The next year he became page to the Grand Master don Antonio Manuel de Villena, who granted him the title of Commander of Aliaga in Aragón. Thus, he received his first title when he was only 14. Soon, he became a Knight of the Order of Malta, which implied lifelong celibacy.

A very traditional, conservative education in many ways.  Though the Jesuits were pretty cutting edge.  But then the Age of Enlightenment polymath side begins to manifest.

In 1729, when he was 16, he returned to Spain and applied for entry to the Royal Company of Marine Guards, the Spanish military school for naval officers. He entered the academy in 1730 and studied modern technical and scientific studies subjects such as geometry, trigonometry, astronomy, navigation, hydrography, and cartography. He also completed his education in the humanities with classes in drawing, music, and dancing. He earned the reputation of being an outstanding student and his fellow students called him Euclid. He finished his studies at the academy in 1734. At the young age of 22, he was given command of a corvette and he participated in the expedition against Oran and the campaign of Naples.

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In 1734, King Philip V of Spain asked Jorge Juan and fellow scientist Antonio de Ulloa to join the French Geodesic Mission organized by the French Academy of Sciences from Paris, under command of the astronomer Louis Godin, and fellow geographers Charles Marie de La Condamine and Pierre Bouguer. The mission was to measure the length of a degree of meridian arc at the Equator in South America and to determine the roundness of the Earth. On 26 May 1735, they left Cadiz in the company of the Marquess of Villagarcía, who had just been appointed Viceroy of Peru. Jorge Juan was on board the ship El Conquistador and Antonio de Ulloa on the frigate Incendio. The expedition traveled to Quito, in present-day Ecuador, and after nine years of careful study, determined that the Earth is not perfectly spherical but is oblate, i.e. flattened at the poles. Juan also successfully measured the heights of the mountains of the Andes using a barometer.

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On his return to Spain, King Ferdinand promoted him to captain. For their work and discoveries in Peru, both he and de Ulloa were elected Fellows of the Royal Society, Juan y Santacilia in 1749.

The Marques de la Ensenada ordered Juan to travel to England secretly to study new naval construction methods and armament of the British. In 1749, he travelled incognito under the name of Mr. Josues and learned all that he could in England (writing back in a numerical cipher), and brought back 50 British naval constructors. In an ironic twist, many of them (including Matthew Mullan and Richard Rooth) went on to build the Spanish ships that would later fight in the American Revolutionary War and the battle of Trafalgar. He was, however, disappointed with the English naval construction methods and upon his return to Spain in 1750, he was placed in charge of Spanish naval construction, creating his own naval construction system (approved in 1752) and improving the shipyards (such as the ones in Cartagena, Cádiz, Ferrol, Havana) and armaments. He implemented modern industrial division of labor among the different disciplines involved in naval construction such as dry-docks, shipyards, furnaces, rigging, and canvas manufacturing.

In 1757, he founded the Royal Astronomical Observatory of Madrid (Real Observatorio de Madrid).

About that undercover trip to England.  Mr. Josues assumed various identities including Able Seaman, French bookseller, and Jewish merchant.