Misappropriations and convergences between the Portuguese methods of navigation and those of the Indian Ocean in the late 15th century

From the 7^th century onwards, ships sailed from China and Vietnam to India and Sri Lanka along the maritime Silk Roads, using magnetic needles and star compasses. Arab and Persian merchants sailing in the Indian Ocean elaborated a universal navigational system, and they invented several nautical instruments. Portuguese explorers, who were ignorant of these techniques, had to significantly develop nautical science as they first ventured into the open sea and sailed towards India in the 15^th century, a process which took 79 years. Their exploration of new maritime routes which required long periods of sailing in the open sea led to the invention of nautical instruments such as the quadrant, the cross-staff and the nautical astrolabe, which resembled earlier Arabic and Persian instruments. The Portuguese navigators only learned about Arabic and Persian nautical science when they met in Kenya in 1498. It is said that Vasco da Gama was led from there to India by the famous Arab navigator Ibn Majid.