Carreira da Índia

The Portuguese India Armadas (Armadas da Índia) were the fleets of ships, organized by the crown of the Kingdom of Portugal and dispatched on an annual basis from Portugal to India, principally Goa. These armadas undertook what is sometimes called the Carreira da Índia ("India Run"), following the sea route around the Cape of Good Hope first opened up by Vasco da Gama in 1497–1499.

For a long time after its discovery by Vasco da Gama, the sea route to India via the Cape of Good Hope was dominated by the Portuguese India armada – the annual fleet dispatched from Portugal to India. Between 1497 and 1650, there were 1033 departures of ships at Lisbon for the Carreira da Índia ("India Run").

The India armada typically left Lisbon and each leg of the voyage took approximately six months. The critical determinant of the timing was the monsoon winds of the Indian Ocean. The monsoon was a southwesterly wind (i.e. blew from East Africa to India) in the summer (between May and September) and then abruptly reversed itself and became a northeasterly (from India to Africa) in the winter (between October and April). The ideal timing was to pass the Cape of Good Hope around June–July and get to the East African middle coast by August, just in time to catch the summer monsoon winds to India, arriving around early September. The return trip from India would typically begin in January, taking the winter monsoon back to Lisbon along a similar route, arriving by the summer (June–August). Overall, the round trip took a little over a year, minimizing the time at sea.

The critical step was ensuring the armada reached East Africa on time. Ships that failed to reach the equator latitude on the East African coast by late August would be stuck in Africa and have to wait until next Spring to undertake an Indian Ocean crossing. And then they would have to wait in India until the Winter to begin their return. So any delay in East Africa during those critical few weeks of August could end up adding an entire extra year to a ship's journey.

...
Wikipedia