The Influence

By making maritime navigation simpler and far more accurate, the Mariner's Astrolabe allowed European sailors to more easily venture out into unknown territories while maintaining knowledge of their position, making exploration by sea less challenging. Furthermore, with more precise navigational equipment, sailors could more easily follow overseas trade routes, lessening shipping time and increasing profits.

Brass frame for increased weight, raising inertia and thus reducing motion

Astrolabe

Mariner's Astrolabe

The most common maps among sailors before the Renaissance were small, highly detailed charts known as portolani. Based mainly around the locations of ports and harbors, these charts were great improvements over the simple twelfth-century maps that preceded them and fine resources for voyages across the seas of Europe. However, as Europeans started to explore Africa and the Middle East with expeditions of much greater length, these portolani began to show their limitations. They failed to represent the Earth's curvature, rendering them useless for voyages of any large lengths.

A renaissance-era copy of the world map from Ptolemy's Geography, displaying Africa, Asia, and Europe. Though not nearly a perfect representation of Earth (it depicts the Atlantic as being only slightly larger than the Mediterranean), it was regarded as the most accurate map of its time.

Prior to the Age of Exploration, Europeans' most common method of maritime navigation was that of using a quadrant to determine the angle of inclination from their position to the Pole Star, Polaris, thus indicating their latitude. This system, though fairly accurate, required very precise positioning of the quadrant, and was consequently extremely difficult to perform at sea. Wind conditions, coupled with the bobbing motion of ships at sea, rendered the quadrant a highly impractical navigational device on the water.

The British East Indiamen were extravagantly expensive to build. Contracts for their construction were awarded by custom and graft. Captains were appointed by patronage rather than education or professional qualifications. And the journeys to Canton (Guangzhon), China, from England in East Indiamen were slow in a trade where fast passages were of value, for example, in guarding the quality of the tea being carried. American merchants were fully aware of these failings of the company and its ships. They set out to gain a foothold in the trade through innovations, particularly after the East India Company’s monopoly in Britain’s China trade was abolished in 1833.

The Portuguese discovered the two large volta do mar (meaning literally turn of the sea but also return from the sea) currents and trade winds of North and of South Atlantic ocean (approximately in the first half and in the late 15th century respectively), that paved the way to reach the New World and return to Europe, as well as to circumnavigate Africa in western open sea, in future voyages of discovery, avoiding contrary winds and currents.

King John II of Portugal continued this effort, forming a committee on navigation.^[18] This group computed tables of the sun's declination and improved the mariner's astrolabe, believing it a good replacement for the cross-staff.^[18]These resources improved the ability of a navigator at sea to judge his latitude.^[18] Castilian Jew Abraham Zacut, the author of an exceptional treatise on astronomy/astrology in Hebrew, with the title Ha-jibbur Ha-gadol, fled to Portugal in 1492. He published in the printing press of Leiria in 1496, the book Biur Luhoth, or in Latin Almanach Perpetuum, which was soon translated into Latin and Spanish. In this book were the astronomical tables (ephemerides) for the years 1497 to 1500, which may have been instrumental, together with the new astrolabe, made of metal and not wood as before^{[citation needed]} (created and perfected at the beginning of the Portuguese discoveries), to Vasco da Gama and Pedro Álvares Cabral in their voyages to India (also passing through South America) around the open Atlantic ocean (including the Southwest Atlantic) and in the Indian Ocean. Nevertheless, the Portuguese had to hire local pilots in the Indian Ocean for several decades to guide their ships.^[28]

In the 15th and 16th centuries, the Crown of Castile and then the "unified" Crown of Spain was also in the vanguard of European global exploration and colonial expansion. The Spanish Crown opened trade routes across the oceans, specially the transatlantic expeditions of Christopher Columbus on behalf of Castile, from 1492. The Crown of Castile, under Charles I of Spain, also sponsored the first expedition of world circumnavigation in 1521. The enterprise was led by Portuguese navigator Ferdinand Magellan and completed by the Spanish Basque Juan Sebastián Elcano. The trips of exploration led to trade flourishing across the Atlantic Ocean between Spain and America and across the Pacific Ocean between Asia-Pacific and Mexico via the Philippines. Later, Andrés de Urdaneta discovered the northern Pacific's volta do mar return voyage.

The compass, a cross-staff or astrolabe, a method to correct for the altitude of Polaris and rudimentary nautical charts were all the tools available to a navigator at the time of Christopher Columbus.^[18] In his notes on Ptolemy's geography, Johannes Werner of Nurenberg wrote in 1514 that the cross-staff was a very ancient instrument, but was only beginning to be used on ships.^[25]

Prior to 1577, no method of judging the ship's speed was mentioned that was more advanced than observing the size of the vessel's bow wave or the passage of sea foam or various floating objects.^[29] In 1577, a more advanced technique was mentioned: the chip log.^[18] In 1578, a patent was registered for a device that would judge the ship's speed by counting the revolutions of a wheel mounted below the ship's waterline.^[18]

Accurate time-keeping is necessary for the determination of longitude.^[25] As early as 1530, precursors to modern techniques were being explored.^[25] However, the most accurate clocks available to these early navigators were water clocks and sand clocks, such as hourglass.^[25] Hourglasses were still in use by the Royal Navy of Britain until 1839 for the timing of watches.^[25]

Continuous accumulation of navigational data, along with increased exploration and trade, led to increased production of volumes through the Middle Ages.^[15] "Routiers" were produced in France about 1500; the English referred to them as "rutters."^[15] In 1584 Lucas Waghenaer published the Spieghel der Zeevaerdt (The Mariner's Mirror), which became the model for such publications for several generations of navigators.^[15] They were known as "Waggoners" by most sailors.^[15]

In 1537, Pedro Nunes published his Tratado da Sphera. In this book he included two original treatises about questions of navigation. For the first time the subject was approached using mathematical tools. This publication gave rise to a new scientific discipline: "theoretical or scientific navigation".

In 1545, Pedro de Medina published the influential Arte de navegar. The book was translated into French, Italian, Dutch and English.^[25]

In 1569, Gerardus Mercator published for the first time a world map in such a cartographic projection that constant-rhumb trajectories were plotted as straight lines. This Mercator projection would be widely used for nautical chartsfrom the 18th century onward.^[30]

In 1594, John Davis published an 80-page pamphlet called The Seaman's Secrets which, among other things describes great circle sailing.^[31] It's said that the explorer Sebastian Cabot had used great circle methods in a crossing of the North Atlantic in 1495.^[31] Davis also gave the world a version of the backstaff, the Davis quadrant, which became one of the dominant instruments from the 17th century until the adoption of the sextant in the 19th century.

In 1599, Edward Wright published Certaine Errors in Navigation, which for the first time explained the mathematical basis of the Mercator projection, with calculated mathematical tables which made it possible to use in practice. The book made clear why only with this projection would a constant bearing correspond to a straight line on a chart. It also analysed other sources of error, including the risk of parallax errors with some instruments; and faulty estimates of latitude and longitude on contemporary charts.

In 1599/1600, Edward Wright's World Chart of 1599 was the first map under the Mercator projection drawn by an Englishman for English navigation. The map prominently displays the Queen Elizabeth I Privy Seal; the only one of her realm to carry her private seal. The Molyneux 1592 globe is the only other cartography with her Privy Seal. Both identify "Nova Albion", the land Captain Francis Drake claimed for his Queen during his 1577-1580 circumnavigation, above the 40th parallel.

In 1631, Pierre Vernier described his newly invented quadrant that was accurate to one minute of arc.^[31] In theory, this level of accuracy could give a line of position within a nautical mile of the navigator's actual position.

In 1635, Henry Gellibrand published an account of yearly change in magnetic variation.^[32]

In 1637, using a specially built astronomical sextant with a 5-foot radius, Richard Norwood measured the length of a nautical mile with chains.^[33] His definition of 2,040 yards is fairly close to the modern International System of Units (SI) definition of 2,025.372 yards. Norwood is also credited with the discovery of magnetic dip 59 years earlier, in 1576.^[33]