The Geography and Meteorology of the N Atlantic Ocean
The story of the Spanish Plata Flotas is not complete without knowledge of the wind systems of our planet! A route from Havana or Vera Cruz to Spain depends heavily upon the planetary wind belts that encircle our planet.
Planetary winds
In a general way, our winds in Florida tend to be mostly easterly (the NE Trade Wind influence), and north of Florida, or S Carolina, the US wind patterns are generally more westerly, as indicated by the direction from which almost all storms come, year round. The exact location of the calm belt, north of which are the Westerlies, varies with the time of the year. It moves north in summer and south in winter.
Masters of ships depending entirely upon the wind for propulsion were, necessarily, acquainted with the wind belts. Coming from the Straits of Florida, the fastest route to Europe was north to the westerly winds which blew them east to Europe. To go by a more southerly route through the lower Bahamas meant bucking the NE Trade Winds all the way to Europe. This was almost impossible with the lateen and square-rigged ships of the Spanish era. Headed north a wind driven old Spanish ship could make about 6 knots at her best, so the north flow of the Gulf Stream added 3 or more knots to her speed, a very significant addition! The winds of the summer were predominately southeast or east and could be counted upon to carry them north. When they reached the latitude of about Cape Hatteras, the winds shifted to the west or northwest and pushed the ships to Europe, aided by the Gulf Stream currents, which also turned east but slowed down somewhat. And this coincidence of wind and currents was used by seamen from shortly after the discovery of the Americas until the advent of steam propulsion permitted ships to steam against wind and currents.
The Gulf Stream System
The Gulf Stream System, which was so important to the slow Spanish sailing ships is a clockwise rotating mass of water going completely around the North Atlantic Ocean. It has no beginning and no end but has rotated ceaselessly for millions of years. It gets its energy from the push of the Northeast Trade Wind belt from east (Africa) to west (Caribbean Sea), south of Florida, and in the northern part of the N Atlantic Ocean, a push from the Westerlies, moving the water back to the east.
The picture overleaf shows how this works and illustrates the path of the Gulf Stream. A result of the rotation of the earth is Coriolis Force, which deflects moving objects in the Northern Hemisphere to the right and in the Southern Hemisphere to the left. Coriolis Force helps turn the wind blown water and form the gyre that we see.