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Originally published in the Historic Nantucket, Vol 44, no. 2 (Fall 1995), p. 82-86

The Gulf Stream Charts of Benjamin Franklin and Timothy Folger
By Captain John Lacouture, USN (ret.)

The Gulf Stream, so named by Benjamin Franklin in 1762, is a mighty river in the ocean that flows from the Gulf of Mexico around the southern tip of the Florida peninsula and along the East Coast, bending off to the northeast when it reaches the vicinity of Cape Hatteras. It continues on to Iceland,the British Isles, and Norway. In the Straits of Florida the Gulf Stream is about forty miles wide and flows at a speed of about five miles an hour. As it progresses into the North Atlantic, it expands to several hundred miles in width and slows to about three miles an hour.

The Gulf Stream carries a greater volume of water than all the rivers of the world combined. It is powered by the rotation of the earth (called the Coriolis Effect), by winds, and by the sun's warming of equatorial waters. As the water warms, its level rises, and it flows toward the lower levels of the surrounding ocean. This movement adds to the volume and force of the Gulf Stream.

The first European to recognize the Gulf Stream as a discrete oceanic current was Ponce de Leon, following his landing in 1513 at what is now St. Augustine, Florida, in search of the Fountain of Youth. When he tried to return to Puerto Rico he found the current to be more powerful than the fair wind before which he was sailing, and his ships were driven to the north instead of southward, his intended course. His pilot, young Anton de Alaminos, adapted his experience with the Gulf Stream by utilizing the current to chart a course for Cortes's treasure ships from Mexico. This course followed the stream to north of the Bahama Islands, then headed east passing near the Bermudas, which the Spaniards soon discovered as they sailed between the Gulf of Mexico and their Iberian homeland. The Spanish sailed the Gulf Stream in their eastward crossings for many years, but kept its existence a secret from all other nations' fleets.

Although some of the early American merchant, whaling, and fishing ships' captains were undoubtedly aware of the Gulf Stream's currents, there were no charts available for universal reference, so its use was limited to those individual navigators with personal knowledge of the stream.

The western portion of the Northeast Current, as it was known before Franklin named it the Gulf Stream in 1762, was first described by Walter Haxton, a captain engaged in shipping tobacco from his Maryland farms to London merchants. In 1735 Haxton drew the first large-scale mariner's chart of Chesapeake Bay, giving detailed soundings and sailing directions. He included, as an addendum to the chart, latitude and longitude points locating the
"Northeast Current" along with estimates of the current's velocity.

Haxton commented:

It is generally known by those who trade to the northern parts of America that the current which comes out of the Gulph of Florida runs constantly along the coast of Carolina and Virginia and considerably further to the Northward, varying its course as it is obstructed by shores. Now if said current always runs nearly in the same part or space of the ocean (as from a great number of Tryals and observations which I have made in 23 voyages to Maryland, I have reason to think it does), the knowledge of its Limits Course and Strength may be very useful to those who have occasion to sail in it.

The British apparently ignored Haxton's description of the Gulf Stream, leaving it up to Benjamin Franklin and Timothy Folger, in 1769-70, to plot the course of the stream and publicize it. They did so to dissuade British mail packets from sailing against the current of the stream in their westward voyages to the American colonies, which added almost two weeks to their crossing time.

Following a varied and generally successful career in the colonies, Franklin went to England in 1754 and was there off and on for twenty years, representing the colonies of Pennsylvania, Georgia, New Jersey, and Massachusetts in various capacities at various times. One of the positions he held while in England was deputy postmaster general and later postmaster general for the American colonies. In 1768, after some years in the job, he questioned why it took the British mail packets so much longer to sail to America than it did most merchant vessels. In the fall of 1768 he discussed his concerns with his first cousin Timothy Folger, captain of a Nantucket merchant vessel.

Folger had grown up on Nantucket, and like so many of the ambitious young men of the period had become involved in whaling, then the island's principal industry. He worked his way up through the ranks and ultimately captained various merchant ships that often sailed to London, where he occasionally called on his cousin Franklin.

During one of those visits, when Franklin voiced his concern about the length of time the British mail packets required to cross the Atlantic, Folger stated that it was obvious to him that British mariners did not know about the powerful current that flowed from west to east across the ocean. He then proceeded to sketch the course of the Gulf Stream on a map that Franklin handed to him and added marginal notes on how to avoid it. That was the first accurate depiction of the Gulf Stream.

In his writings at a time when 150 Nantucket whaling vessels were under sail, Franklin quotes Folger as stating:

... whales are found generally near the edges of the Gulph Stream, a strong current so called which comes out of the Gulph of Florida passing Northeasterly along the Coast of America and turning off most Easterly, running at the rate of 4, 3 1/2, 3, and 21/2 miles an Hour, that the whaling Business leads these people to cruise along the Edges of the Stream in quest of whales, they are become better acquainted with the Course Breadth, Strength and extent of the same than those navigators can well be who only cross it in their Voyages to and from America, that they have opportunities of discovering the strength of it when their boats are in pursuit of this Fish, and happen to get into the stream while the Ship is out of it, or out of the Stream while the ship is in it, for then they separated very fast and would soon lose sight of each other if care were not taken.

Franklin had Folger's chart printed and distributed to British packet captains in 1769 or 1770, but they tended to ignore it, perhaps because they couldn't admit that colonial fishermen knew more about the ocean than did highly trained and experienced British mariners. When the American Revolution commenced, Franklin ceased distribution of the chart to prevent the British fleet from having the advantage of such valuable information.

In March of 1775 Franklin left London and sailed for home. The next year he was sent as envoy to Paris to negotiate a treaty with the French government. During those two transatlantic crossings Franklin tested the temperature of the Gulf Stream and learned that it was warmer than the surrounding waters. The discovery renewed his interest in the Timothy Folger chart, and he had it copied and printed by Le Rouge following his arrival in Paris. He intended to provide copies to all French ship captains carrying arms and supplies to the American colonies.

The original Folger charts — as printed for and distributed by Franklin — disappeared and were assumed lost for almost two centuries until September 1978, when Philip L. Richardson of the Woods Hole Oceanographic Institution found two copies in the Bibliotheque Nationale in Paris. They were most likely obtained and saved by the French during the years from 1776 to 1785 when Franklin was envoy to France for the American colonies. He was extremely successful in that capacity, prompting the French to supply weapons and ships to the American forces.

One famous example is the Bonne Homme Richard, the ship on which John Paul Jones fought his most spectacular battles, and on which several Nantucket men bravely served. The French christened the ship in Franklin's honor, taking the name from his Poor Richard's Almanac. Following the crucial American victory at Saratoga in 1777, Franklin persuaded the French government to form a military alliance with the colonies, ultimately ensuring Washington's victory at Yorktown when French warships under the command of the Marquis de Grasse prevented reinforcements from reaching the British troops.

In 1786, after the Revolutionary War, Benjamin Franklin published Folger's sketch of the Gulf Stream as part of an article in the Proceedings of the American Philosophical Society of Philadelphia. In the article, Franklin wrote:

The Nantucket whalemen, being extremely well acquainted with the Gulf Stream, its course, strength and extent, by their constant practice of whaling on the edges of it, from their Island quite down to the Bahamas, this draft of that stream was obtained from one of them, Captain Folger, and caused to be engraved on the old chart in London for the benefit of navigators by B. Franklin.

When the Folger-Franklin chart is compared to the most modern charts of the Gulf Stream, derived from sensitive infrared photographs taken from satellites, it is remarkable how accurately that 1768 chart depicts the path of the great "river in the ocean."