<P> In the thirteenth century they were guided by the sun position . For celestial navigation like other Europeans, they used Greek tools, like the astrolabe and quadrant, which they made easier and simpler . They also created the cross-staff, or cane of Jacob, for measuring at sea the height of the sun and other stars . The Southern Cross became a reference upon the arrival of João de Santarém and Pedro Escobar in the Southern hemisphere in 1471, starting its use in celestial navigation . The results varied throughout the year, which required corrections . To address this the Portuguese used the astronomical tables (Ephemeris), a precious tool for oceanic navigation, which spread widely in the fifteenth century . These tables revolutionized navigation, enabling latitude calculations . The tables of the Almanach Perpetuum, by astronomer Abraham Zacuto, published in Leiria in 1496, were used along with its improved astrolabe, by Vasco da Gama and Pedro Alvares Cabral . </P> <P> The ship that truly launched the first phase of the discoveries along the African coast was the Portuguese caravel . Iberians quickly adopted it for their merchant navy . It was a development based on African fishing boats . They were agile and easier to navigate, with a tonnage of 50 to 160 tons and one to three masts, with lateen triangular sails allowing luffing . The caravel particularly benefited from a greater capacity to tack . The limited capacity for cargo and crew were their main drawbacks, but have not hindered its success . Limited crew and cargo space was acceptable, initially, because as exploratory ships, their "cargo" was what was in the explorer's discoveries about a new territory, which only took up the space of one person . Among the famous caravels are Berrio and Caravela Annunciation . Columbus also used them in his travels . </P> <P> Long oceanic voyages led to larger ships . "Nau" was the Portuguese archaic synonym for any large ship, primarily merchant ships . Due to the piracy that plagued the coasts, they began to be used in the navy and were provided with cannon windows, which led to the classification of "naus" according to the power of its artillery . The carrack or nau was a three - or four - masted ship . It had a high rounded stern with large aftcastle, forecastle and bowsprit at the stem . It was first used by the Portuguese, and later by the Spanish . They were also adapted to the increasing maritime trade . They grew from 200 tons capacity in the 15th century to 500 . In the 16th century they usually had two decks, stern castles fore and aft, two to four masts with overlapping sails . In India travels in the sixteenth century used carracks, large merchant ships with a high edge and three masts with square sails, that reached 2,000 tons . </P> <Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (July 2012) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Who traveled with conquistadors in order to convert the natives they encountered