dank des Monsuns nicht schwer, Reisen bis nach Indonesien ( und somit auch bis Indien) waren ohne weiteres möglich und sind ein Grund dafür, dass Indonesien heute überwiegend muslimisch ist.

Indian Ocean and the Monsoon Trade: There are no barriers to trade along the coast between the Red Sea and Japan. Local coastal routes soon were linked and extended to Indonesia. By about 850 trade was mostly in Muslim hands. This trade brought Hinduism and later Islam to Indonesia. A great advantage in the Indian Ocean is the monsoon which blows south in the winter and north in the summer. Someone in the Arabian Peninsula wishing to go to Africa or Indonesia would go south on the winter monsoon and return north with the summer monsoon. In Africa this trade extended about as far as Mozambique, at the southern limit of monsoon winds. Further south was a lee shore with no trade goods that could not be obtained further north. It is not clear how far south trade and geographic knowledge extended, but there is said to be a Chinese map of the thirteenth century showing Africa in roughly its true shape and there is a Venetian report from the mid-fifteenth century of a Chinese or Javanese junk seen off the southwest African coast.

Winds in the Age of Sail - Wikipedia

Indischer Monsun – Wikipedia