Medieval Sailing
During the early Middle Ages, sailing ships on the Mediterranean sea continued to use the triangular sail developed during the Roman Empire. As time went on, ship-builders experimented with using more than one mast. By 1000 AD, Italian merchants from Venice and Genoa and Pisa were sailing in ships with three masts, each with a triangular, or lateen, sail. Using three masts let sailors adjust even better to changes in the wind.
Still, Mediterranean sailors in the Middle Ages had an important unsolved problem. They wanted to sail south along the Atlantic coast of Africa, to trade with West Africa by ship instead of across the Sahara. It would be much cheaper to bring African gold north by ship than by camel. They could sail south to West Africa just fine, but then they couldn't sail back, because the winds along the coast almost always blew south and not north. In addition, medieval sailors couldn't sail any further south, to explore South Africa, because the water current ran north along the coast. In order to sail here, you would need to be able to tack: a method of moving the sail back and forth that lets you sail into the wind. Portuguese ship-builders figured out how to combine square sails and the lateen sail to sail north even when the wind is blowing south.
Vasco da Gama and Columbus used ships like these
Once Portuguese ship-builders had figured out how to sail along the coast of Africa, they became interested in sailing right across the Atlantic Ocean itself, towards China (well, really towards North America, but they thought they would get to China). Portuguese sailors had just gotten hold of a Chinese invention - the compass. The compass, combined with the astrolabe, made it possible to tell which way you were going even when you were out of sight of land.
But to prepare for crossing the Atlantic, ship-builders also redesigned their sails: Both Vasco da Gama and Columbus used three masts, the two front ones with square sails, and the back mast with a lateen sail.
To find out more about medieval sailing, check out these books from Amazon or from your local library:
I.C. Campbell, "The Lateen Sail in World History", Journal of World History 1995
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