I have posted from time to time on the subject of ancient sea travel and this is a good point to pull together some thoughts.
My first point is that historical interpretation has been hugely conservative; mostly taking the position that it was all invented in the past five centuries and almost nothing came before. In the process, an intellectual edifice was constructed that is only slowly been eroded.
I have a different stance. Sea travel requires two preconditions, economic opportunity and technology. Put that in place and you can count on foolish young men to do the rest.
The big technical issue has been the challenge of sailing into the wind. Yet I think that this came into play as soon as the sail was fabricated. A small skiff and a bit of horse play and you will figure something out. After all, the simplest working deal needs only two sails closely rigged and someone would have observed the erratic change in behavior and put it together.
The real problem was the size of the vessel. Sailing into a mere three foot wave in a ladened small open canoe under sail is a sure way to get killed. The vessel needs size and certainly closure to avoid been swamped, viking long boats notwithstanding which used oars mostly when challenged.
All this was well solved with the advent of metal for the making of axes. Boards could be shaped and fitted to form a snug ship that was able to sail into the wind and survive. This means that the technical means to develop useful sailing ships came into existence with the Bronze Age at the same time as the economic need arose.
Thus we have in the West, the emergence of the Mediterranean fleets and the Atlantean fleets from as early as even 3000 BCE through a Bronze Age
ending in 1159BCE. The shipping then contracted to the high point Mediterranean and the Atlantic sea board until late fifteenth century AD. The industry was crippled by the loss of most of the copper trade coming from the Americas and became internal to the Roman Empire. This meant a high level of trade efficiency and little profit chasing old markets. It is noteworthy that Caesar faced large ocean going ships in the Bay of Biscay superior to his shipping.
Atlantic was a closed of sea that was difficult to exit or enter.
Indian Ocean was a lot smaller and trips were quicker and far more predictable. Thus we have the Arab Dhow which is also quite seaworthy and hauled goods around the edges of the sea. A smaller vessel could make it work economically and live in its seas.
Then we come to the
South China Sea and the open Pacific. Here longer voyages and large profitable cargos became possible. What emerges is the large seagoing junk that was not matched in the Atlantic until the eighteenth century. The development of the junk will also go back to the Bronze Age and reached its apogee under the Ming Dynasty.
Again, they were part of a circumscribed ocean that was hard to get out off. It was also large and empty. However a great circle route does exist and is easily discovered. It is not nearly so tricky as the
Atlantic. So we cannot be surprised to find large ships and landfalls along the West Coast of the . Americas
The economic value of these outposts was plausibly minimal, but those into
SE Asia were very profitable. The main copper and bronze supply for China could well have come from the Mekong.
My point is that technical ability came quickly and exploited opportunity early. The adventurers were always there.