In 1768, while in England, colonial postmaster Benjamin Franklin heard a curious complaint from the Colonial Board of Customs about it taking several weeks longer for a ship from London to Boston than one coming the other direction.
His cousin Timothy Folger, a Nantucket whaler, told him the difference was because of the Gulf Stream, observable by whale behaviour (they tend to stay at its edges), water's temperature, and water's color. It’s a river in the ocean 100 kilometres wide and a thousand meters deep, that can top 5 mph; It could supply the energy of several nuclear plants.
Ocean currents redistribute the heat of the sun, affect weather and ocean nutrients. Northern Europe is warmer because the Gulf Stream, which has weakened in recent years and there is concern that it could stop due to global warming;
But the whalers did not discover the Gulf Stream. Columbus encountered it, and Ponce de Leon in 1513 called it "A current … more powerful than the wind." However, all the crown cared about was his failure to find gold.
Franklin had Folger sketch the path of the current which he forwarded to the British Post Office. A map printed in 1769 in London was mostly ignored by British sea captains.
However, a few years later as ambassador to France. Franklin gave the map to the French hoping it would help in speeding supplies to the rebels.