I saw an article a while back, sorry no reference, about an abacus found in South America, made of native South American wood and so forth, and dated to around 1200 AD, that was basically identical to Chinese ones of the same time, in terms of style, number of rows of beads, and so on. The implication was that trading ships from China had probably made it to the west coast of South America around that time.
It is written in China that 250,000 'took to the sea' at the collapse of the Shang Dynasty.