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24-636: The Alderney Race is 8 nautical miles (15 km; 9.2 mi) across and located roughly between Alderney, in the Bailiwick of Guernsey , and La Hague, France. It constitutes the northeastern limit of the Gulf of Saint-Malo . When the wind and the race current flow in opposite directions, the sea becomes particularly chaotic: wave heights can reach 4 metres (13 ft) and have wavelengths smaller than 50 metres (164 ft). The waves break with violence, thus making shipping conditions particularly dangerous. On

48-599: A coordinate system with parallels of latitude and meridians of longitude . The earliest reference of 60 miles to a degree is a map by Nicolaus Germanus in a 1482 edition of Ptolemy 's Geography indicating one degree of longitude at the Equator contains " milaria 60 ". An earlier manuscript map by Nicolaus Germanus in a previous edition of Geography states " unul gradul log. et latitud sub equinortiali formet stadia 500 que fanut miliaria 62 ⁠ 1 / 2 ⁠ " ("one degree longitude and latitude under

72-588: A quarter meridian . So ⁠ 10,000,000 m / 90 × 60 ⁠ = 1,851.85 m ≈ 1,852 m became the metric length for a nautical mile. France made it legal for the French Navy in 1906, and many metric countries voted to sanction it for international use at the 1929 International Hydrographic Conference. Both the United States and the United Kingdom used an average arcminute—specifically,

96-406: A degree (5866 ⁠ 2 / 3 ⁠ feet per arcminute ). In 1633, William Oughtred suggested 349,800 feet to a degree (5830 feet per arcminute). Both Gunter and Oughtred put forward the notion of dividing a degree into 100 parts, but their proposal was generally ignored by navigators. The ratio of 60 miles, or 20 leagues, to a degree of latitude remained fixed while the length of the mile

120-579: A minute of arc of a great circle of a sphere having the same surface area as the Clarke 1866 ellipsoid . The authalic (equal area) radius of the Clarke 1866 ellipsoid is 6,370,997.2 metres (20,902,222 ft). The resulting arcminute is 1,853.2480 metres (6,080.210 ft). The United States chose five significant digits for its nautical mile, 6,080.2 feet , whereas the United Kingdom chose four significant digits for its Admiralty mile, 6,080 feet. In 1929

144-459: A test descent. Inventions or Devises , published in 1578, is one of William Bourne's more important works. This book gives many guides and instructional tools for sailors, mostly concerning interactions with other ships. The 21st device listed is the earliest known description of a ship's log and line , which he attributes to Humprey Cole , an officer of the Tower Mint . The 75th device on

168-428: Is a unit of length used in air, marine, and space navigation , and for the definition of territorial waters . Historically, it was defined as the meridian arc length corresponding to one minute ( ⁠ 1 / 60 ⁠ of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees). Today the international nautical mile

192-482: Is defined as 1,852 metres (about 6,076 ft; 1.151 mi). The derived unit of speed is the knot , one nautical mile per hour. There is no single internationally agreed symbol, with several symbols in use. The word mile is from the Latin phrase for a thousand paces: mille passus . Navigation at sea was done by eye until around 1500 when navigational instruments were developed and cartographers began using

216-517: The Sea. Bourne was critical of some aspects of the original and produced a manual of more practical use to the seaman. He described how to make observations of the sun and stars, using a cross-staff , and how to plot coastal features from the ship by taking bearings using triangulation. Before publishing his submarine design, William Bourne was a jurat in Gravesend, England. His name first appears in

240-615: The contrary, when the wind and the stream flow in the same direction, the sea becomes calm, provided that the tidal coefficient is not too great. The uneven seabed – both Alderney and La Hague lie in the Armorican Massif – makes the situation more complicated. Bad weather can produce abundant wind-blown foam, making visibility poor. During good weather, opposing wind and currents can cause breaking waves, especially at Banc de la Schôle and at Longis Bay in Alderney. The power of

264-599: The current comes from the narrowness of the strait and from the fact that there is a 2-metre (6 ft 7 in) tidal height difference between Carteret and La Hague as well as between la Hague and Cherbourg . Because of the enormous potential it sees in tidal power, the French government plans to use tidal turbines to tap the energy of the Race. 49°43′N 2°04′W  /  49.72°N 2.07°W  / 49.72; -2.07 Nautical mile A nautical mile

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288-636: The description was a general principle rather than a detailed plan. However, the concept of an underwater rowing boat was eventually put into action by the Dutchman Cornelius Drebbel in 1620, and Nathaniel Symons demonstrated a 'sinking boat' in 1729 using the expanding and contracting volume of the boat to submerge. The submarine was the subject of a modern-day recreation on season 3 of " The Re-Inventors " TV show, episode "Bourne Submarine". The recreation had limited functionality before it sank when water pressure ruptured some membranes on

312-504: The distance along a great circle was 60 miles per degree. However, these referred to the old English mile of 5000 feet and league of 15,000 feet, relying upon Ptolemy's underestimate of the Earth's circumference . In the early seventeenth century, English geographers started to acknowledge the discrepancy between the angular measurement of a degree of latitude and the linear measurement of miles. In 1624 Edmund Gunter suggested 352,000 feet to

336-480: The equator forms 500 stadia , which make 62 ⁠ 1 / 2 ⁠ miles"). Whether a correction or convenience, the reason for the change from 62 ⁠ 1 / 2 ⁠ to 60 miles to a degree is not explained. Eventually, the ratio of 60 miles to a degree appeared in English in a 1555 translation of Pietro Martire d'Anghiera 's Decades: "[Ptolemy] assigned likewise to every degree three score miles." By

360-478: The first charter of incorporation of Gravesend from June 5, 1562. His name appears once again as a jurat in the second charter of Gravesend, June 5, 1568. During the time of the second charter, the only records of regulations for trading in Gravesend are written in Bourne's handwriting. This would imply that he held an office such as clerk of the market. He also worked as an innkeeper during this time, one of fourteen in

384-572: The international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as exactly 1,852 metres (which is 6,076.12 ft). The United States did not adopt the international nautical mile until 1954. Britain adopted it in 1970, but legal references to the obsolete unit are now converted to 1,853 metres (which is 6,079.40 ft). The metre

408-630: The late 16th century English geographers and navigators knew that the ratio of distances at sea to degrees was constant along any great circle (such as the equator , or any meridian), assuming that Earth was a sphere. In 1574, William Bourne stated in A Regiment for the Sea the "rule to raise a degree" practised by navigators: "But as I take it, we in England should allowe 60 myles to one degrée: that is, after 3 miles to one of our Englishe leagues, wherefore 20 of oure English leagues shoulde answere to one degrée." Likewise, Robert Hues wrote in 1594 that

432-463: The list is a description of a night signal or early semaphore system to be used between people on distant ships who had previously decided on a code consisting of a series of lights and fashion of standing. The 110th entry is what seems to be a type of telescope . The device was said to have been employed by mathematician and surveyor Leonard Digges and Bourne was asked to investigate it by Queen Elizabeth I 's chief advisor Lord Burghley . Bourne's

456-499: The location. William Bourne (mathematician) William Bourne (c. 1535–1582) was an English mathematician, innkeeper and former Royal Navy gunner who presented the first design for a navigable submarine and wrote important navigational manuals. He is often called William Bourne of Gravesend . In 1574, he produced a popular version of the Martín Cortés de Albacar 's Arte de Navegar , entitled A Regiment for

480-430: The measurement based on this ( ⁠ 40,075.017 km / 360 × 60 ⁠ = 1,855.3 metres) is known as the geographical mile . Using the definition ⁠ 1 / 60 ⁠ of a degree of latitude on Mars , a Martian nautical mile equals to 983 m (1,075 yd). This is potentially useful for celestial navigation on a human mission to the planet , both as a shorthand and a quick way to roughly determine

504-403: The poles and 1,843 metres at the Equator. France and other metric countries state that in principle a nautical mile is an arcminute of a meridian at a latitude of 45°, but that is a modern justification for a more mundane calculation that was developed a century earlier. By the mid-19th century, France had defined a nautical mile via the original 1791 definition of the metre , one ten-millionth of

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528-426: The town of Gravesend. His design, detailed in his book Inventions or Devises published in 1578, was one of the first recorded plans for an underwater navigation vehicle. He designed an enclosed craft capable of submerging by decreasing the overall volume (rather than flooding chambers as in modern submarines), and being rowed underwater. Bourne described a ship with a wooden frame covered in waterproofed leather, but

552-491: Was originally defined as 1 ⁄ 10,000,000 of the length of the meridian arc from the North pole to the equator (1% of a centesimal degree of latitude), thus one kilometre of distance corresponds to one centigrad (also known as centesimal arc minute) of latitude. The Earth's circumference is therefore approximately 40,000 km. The equatorial circumference is slightly longer than the polar circumference –

576-453: Was revised with better estimates of the earth’s circumference. In 1637, Robert Norwood proposed a new measurement of 6120 feet for an arcminute of latitude, which was within 44 feet of the currently accepted value for a nautical mile. Since the Earth is not a perfect sphere but is an oblate spheroid with slightly flattened poles, a minute of latitude is not constant, but about 1,862 metres at

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