The Technology of Ocean Voyages

Sailing south along the African coast was easy going before 1450: following winds, familiar landmarks, short hops. Getting back meant sailing north into the same winds that had pushed you south. The square sails on older European ships only caught wind from behind, so a straight return was nearly impossible. The caravel solved this with the lateen sail, a triangular sail set at an angle along the ship's length rather than square across it. Angled correctly, it lets a ship sail close to the wind, tacking in a zigzag to make progress against a headwind, something a square rig simply cannot do.

Once ships could cross open ocean out of sight of land, sailors needed a way to know where they were. The astrolabe answered this for latitude: at local noon, when the sun reached its highest point, a navigator measured the angle between the sun and the horizon. That angle, combined with tables for the date, gave latitude, how far north or south of the equator the ship sat. It said nothing about longitude, east-west position, which remained a guessing game until much later.

Portuguese sailors also mapped the Atlantic's wind and current wheels: westerlies blowing eastward across the North Atlantic, trade winds blowing westward further south, with current patterns circulating alongside them. Fighting straight home against a headwind was slow. The volta do mar, the turn of the sea, meant sailing far out into open ocean to catch the westerlies, then riding them back to Europe. This system of sail, instrument, and wind knowledge is what let voyages become round trips, setting up the Columbian Exchange and the silver trade that followed.