“Know that learning leaves a trail and a scent proclaiming its possessor, a ray of light and brightness shining on him, pointing him out.”

— Abdsal-Latif al Baghdadi, 13th century Mideast scholar & historian

We had spent a long, tense day on my yawl, Nimble, with dark squalls and lightning slowly overtaking from astern all the while closing obliquely with Montauk at the end of Long Island. Through the gloaming, we saw white surf pounding the boulders — some the size of cottages — lining the beach, sometimes totally hidden beneath the rolling swells.

In the past four centuries, this coast had claimed hundreds of ships.

The squalls closed over us with rolling thunder and torrential rain and the coast vanished. We were sailing so fast that the lightning chain trailed aft to protect us against a strike.

I looked at our electronic Global Positioning System. We were precisely north of the equator at 41 degrees, 1.5 minutes north latitude, and west of the prime meridian in Greenwich, England at 71 degrees 55 minutes west longitude. I looked at the NOAA chart #13205 next to me. It was based on North American Datum of 1983, corrected in 1995, accurate and reliable — if you knew where you were.

Knowing — or not knowing — exactly where we were could mean a safe harbor, or shipwreck. “Beep, beep, beep” sounded the GPS alarm, which was displaying: “Poor GPS Signal.” I switched it to a view of the sky showing the position of each NOAA navigational satellite sending position signals to my unit. One by one they were blinking out

I switched back to the current position display and instead witnessed — flashing back in time in reverse sequence — locations entered since I first started logging data in this system: Turkey Point, Tangier Island, Ragged Point … and in a trice, hundreds of way points recorded over two years were gone. The display went dead, and we were at serious risk in deteriorating weather.

Nearly a thousand years earlier, mariners had no compass. The meaning of “position” on the face of the earth awaited the understanding of our planet’s global nature, and the development of latitude and longitude as ideas.

What brave people the Norsemen were, testing the limits of the known world, eager to understand what lay beyond the pale, and to harvest the resources hidden there. European explorers, having ranged the Mediterranean for millennia, had tried the edges of mysterious Africa but it would be another 260 years before Marco Polo would visit the Orient and return to tell of its wonders.

Vikings from today’s Scandinavia pressed west to explore the New World shortly after 1000. While some archaeologists claim Vikings never reached the Chesapeake, others disagree.

One can interpret the Hauk Book Sagas which chronicle the adventures of Thorfinn Karlsevni as describing coastlines far south of the presumed Newfoundland Viking limits. “Straumfjiord” may well be the Hudson River, and the tidal lake of “H’op,” where Karlsevni spent part of the summer in 1011 with a few longships, as the Chesapeake. We have no concrete evidence yet; perhaps we’ll never be sure.

We know that Vikings came to the New World, yet know only a little of how they navigated.

Exploring or fishing a few days northwest from the Faroe Islands, north of Scotland and under just the right conditions, they could encounter mirages of shimmering mountains above the horizon of these frigid seas.

These vanish on approach, but if a curious mariner persisted with a favoring wind, it’s only about 300 nautical miles to Greenland. A similar leap of faith from Greenland leads to Baffin Island, and south from there is the North American coast.

The mirages were rare and with no landmarks, an accurate course is all important. Knowing the sun’s direction enabled them to use a sun compass. If, for example, one watches the sun rise to its highest point, the shadow it casts (at this local noon) points exactly north. Bisecting the angle between two readings equidistant before and after noon will determine south, though not very quickly.

(Today, one can find direction with any analog watch [one that has hands] that has a revolving bezel marked with the compass points. The procedure differs slightly from morning to afternoon. In the a.m. hours, point the hour hand directly at the sun and rotate the direction ring or bezel so south bisects the angle between the hour hand and 12:00. At noon, of course, both hands point south. In the p.m. hours, point the hour hand at the sun and rotate the bezel so south is bisecting the angle with noon. When a watch is so oriented, all of the cardinal compass points on the rotating bezel will be correct.)

Unfortunately, early navigators lacked devices that told time. This was the crux of the problem of navigation at sea.

In the far northern latitudes, where even a magnetic compass is often unreliable, the direction of the sun can be more trustworthy. But direction is also vital in storm, fog and under overcast skies — precisely when ships get into trouble. In the Icelandic Flateyjarbok, the Saga of St. Olaf describes a “Solarsteinn” or sunstone, by which mariners claimed to be able to tell the direction of the sun when it was obscured by cloud or fog.

Some Viking experts, like William Fitzhugh at the Smithsonian, dispute the sunstone claim, but others believe it was Icelandic spar, the dichroic mineral cordierite. It is a transparent form of calcite and natural light passing through it is double refracted, so that even through cloud or fog, a sun image can be projected. The principle, rediscovered during World War II, was used to make a polariscope to help aerial navigators find their way when magnetic compasses failed on transpolar flights.

The directional properties of magnetite, a form of iron ore, were known in antiquity but the use of that lodestone to impart magnetism to a compass needle came much later, around 1187, a discovery traditionally associated with Italy’s port of Amalfi. The magnetized needle could be floated on a reed in a bowl of water and would indicate north. Because iron loses its magnetism, it had to be periodically refreshed by rubbing or stroking it with lodestone.

Some mariners indicated that poor compass performance resulted from failing to do this. Lodestones, also known as adamants, sailing pieces or sailstones, appeared in inventories of the ship, Plenty at Hull, of England, in 1410-1412.

The compass needle suspended on a point or pivot was in use and considered essential by 1218.The resulting compass was eventually suspended on a gimbal, which allowed it to tilt in any direction when a ship was rolling and pitching in several directions at one time. Navigator Martin Cortes was the first to write of gimbals in 1545.

In the Chesapeake, John Smith used a small pocket compass to mystify Chief Opechanchanough. Some credit his making a present of this to his captor, and not the intervention of Pocahontas, with saving his life.

The compass cardinal points were already in the mariner’s lexicon, and were known as “the rhumbs of the winds,” first in the Mediterranean, and eventually spreading to the rest of Europe.

Once the ability to carry direction was sure, a course could be maintained in darkness and unfavorable weather, and if direction had to be changed by virtue of wind or some hazard, one could steer back to an original heading.

That required carefully estimating progress in each direction during each course diversion. This was accomplished, even by illiterate seamen, using a traverse board, an early clipboard device with the compass points carved onto it and a simple system of strings on pegs for each successive helmsman to record how many turnings of the sandglass they’d sailed on each heading, and at what speed the ship had sailed.

Speed was tracked using a “chip log” a ballasted board on a long line or cord which when thrown overboard, would float upright in the sea. Its drag would pull or pay out the line as the ship sailed away from it. The line had knots at specified distances and a sailor would count them as they ran out through his fingers. Another man would time the process as sand flowed through a small half-hour sandglass. As the last grains fell, he would cry “mark” and the line tender would stop it running out. Speed was equal to the number of knots plus the fathoms (6-foot increments) past the last knot, to give fractions. It’s obvious where “knots,” the mariners’ measure of speed, came from.

This once crude measure is now standardized worldwide, and the knot, one nautical mile in one hour, is also one 60th of a degree of latitude.

The Greeks discovered in antiquity the numerical relationship between celestial altitudes and the observer’s latitude, or distance from the equator. People also recognized the temperature changes and the changing declination (height) of the sun at noon as one moved north and south. Several instruments were subsequently been used by Arab and European navigators to measure altitude.

Mideast surveyors developed the astrolabe, a device that measured the height of the sun or other bodies in the sky. This instrument was hung plumb from a ring at the top to establish the vertical/horizontal reference. With proper data on the sun’s declination through the year, surveyors could measure the distance between far flung cities.

While astrolabes hung from tripods on land could achieve accuracy of 15 minutes of arc (a quarter degree) or better, shipboard use presented difficulties. An assistant had to dangle the instrument steadily — while standing on the rolling deck — as the navigator aligned the sighting vane. Its accuracy was probably not better than 30 miles, or half a degree of latitude.

The astrolabe became the principle tool for astronomical observations from ancient times through the Middle Ages. One brass astrolabe in a Saudi Arabian museum weighs 17 pounds.

One of the simplest latitude tools, favored by Northern Europeans, consisted of a calibrated stick, with a second moveable cross member called a “cross staff,” or “transverse” to determine the angle of the sun or other object above the horizon.

Holding one end of the staff against his temple, the user would sight the body (usually sun or north star) at the top edge of the transverse, and slide it toward or away from his eye until the bottom edge simultaneously aligned with the horizon. The angle could then be read from the staff at its intersection with the transverse. At low angles of altitude the cross staff had a potential accuracy within 5–10 minutes of arc — which translates into 5–10 miles of north-south position.

The tool did have its drawbacks. Many 17th century master mariners had one eye that was nearly blinded, or impaired when the cornea became permanently clouded after directly sighting the sun.

The cross staff and astrolabe seem to have been companions in the navigator's kit during the 15th and 16th centuries.

The “back staff,” or “Davis Quadrant,” introduced by Englishman John Davis about 1600, became a favorite throughout the 17th and 18th centuries. It protected vision because the user faced away from the sun, simultaneously sighting the horizon through a slot while aligning the sun’s shadow with the same slot. Davis improved the arc scale and allowed readings within 10 minutes, giving more accurate positions for higher altitudes of the sun

Meanwhile, the astrolabe was modified to a “quadrant” — a quarter-circle protractor — with a plum-bob hanging from the apex, and sights along one edge. The radius was typically about 12 inches, large enough to read to about a quarter degree.

In the 18th and 19th centuries, “octants” and “sextants” eventually incorporated lenses, mirrors, a Vernier and later, the worm-gear micrometer scale. These led, under ideal conditions, to accuracy within two-tenths of a minute of arc (0.2 miles). The final version, the sextant, continued in common use for navigation right into the 1980s.

Knowing latitude allowed mariners to “sail a line” — east to west and vice versa — maintaining a constant distance between the pole and equator.

This is how the adventurers to the Chesapeake colony crossed the Atlantic. They sailed south along the coast of Europe to the latitude of the trade winds, then held a course of known latitude until they ran up on the Caribbean Islands, then north to our continent. It was decades before English navigators figured out they could sail a course directly from England to the Virginia colony, saving many weeks.

But latitude, now well understood was not the real problem: Longitude, the distance east to west, was.
Mariners could only estimate distance traveled, “the reckoning” using their chip logs. Christopher Columbus kept a hidden reckoning during his first voyage so as not to frighten his crew with the vast width of the Atlantic. It was all a process of educated guess.

When Christopher Newport came across to the Caribbean and then sailed up to the Chesapeake in 1607, his approach to the coast was fraught with danger after some weeks at sea, because he had no idea where he was except that he had sailed into latitude 36 north. They had sailed three days beyond where the reckoning had placed their ship and found no land.

The fleet of three ships reconnoitered and Captain Ratcliffe on the Discovery voted to give up and return to England. That night, a storm struck and further confounded their reckoning, the ships driving uncontrolled before the gale. Had they known how close to disaster they were on the sandbars of Virginia and North Carolina’s Outer Banks, they might have despaired.

A member of the expedition, Thomas Studley, later wrote: “God the guider of all good actions … did drive them by his providence to their desired port, beyond all their expectations; for never any of them had seen that coast.” Or pure luck.

During the great voyages of discovery, the loss of a rival nation’s ships at sea was helpful to one’s own cause. The loss of life was irrelevant, and it was the greatest fortune — often supported by letters of marque from one’s ruler — to plunder such disasters. The routes of passage, sailing directions, watering and victualing places were all closely held secrets and even techniques of navigation were kept from largely illiterate crews by often semiliterate mariners. Technology developed slowly and was slow to spread.

Navigational data, such as could be written, was kept in documents called “rutters,” pocket-size route books with handwritten lists of courses between known capes or islands, and advice about currents or tides. While these must have been used very early, the first known printed one came from Venice in 1490.

The first English rutter, published in London in 1528, was translated from an earlier French “Le Routier de la Mer” of 1502. Many of these old rutters have been preserved in European archives, but only a few have been examined, or unscrambled by modern scholars.

These were early versions of what today is NOAA’s nine-volume United States Coast Pilot, Volume 3, which discusses virtually every creek and shore from Sandy Hook, NJ to Cape Henry, VA; all of Jersey and the Chesapeake in about 250 pages.

John Smith on his second voyage from England to the New England Coast (which he so named), found that the charts for these shores were “…no more good then so much waste paper.” He charted them anew and once again in England, drew on his experience to write “An Accidence or The Path-way to experience Necessary for all Young Sea-men” in 1626. This was later revised as John Smith’s “A Sea Grammar.”

Such was the effort to compensate for an inability to determine longitude other than by dead reckoning and luck.

What was needed to track longitude was the ability to keep time; to accurately track the sun as it appeared to circle the globe at a 1,000 miles per hour — a few seconds’ error could put one miles off. At Greenwich, one knew exactly where one was at solar noon, but far at sea, when solar noon came, it was many hours later (or in the Pacific, earlier) than in England.

The sun’s apparent travel — earth’s turning — could be measured as an angle, the 15 degrees of “hour angle” which summed to just 24 hours as the circle around the globe was observed. It would be necessary to carry that time accurately within a few seconds — two or three a month — if any timepiece were to be useful to the mariner in danger at sea. Anything less and the inaccuracy could put one ashore or on a rock. Famed English diarist Samuel Pepys, late in the 17th century, wondered “that there are not a great deal more maritime disasters than there are.”

In Europe, accurate pendulum clocks had been developed that could be coordinated with known movements of celestial bodies. When such a clock was taken to sea, however, the ship’s movement bollixed up the pendulum and accuracy was immediately lost.

To meet this need, the British Parliament in 1713 established a set of three Longitude Prizes totaling £25,000 sterling, to the genius who could solve the problem of catching time at sea.

Galileo, in 1610, discoverer of Jupiter’s moons, also noted that they were, like our own moon, near perfect timekeepers in their orbits, emerging and disappearing behind the planet.

The French astronomer Jacques Dominique Compte Cassini used this device to measure the true area of France, finding it 20 percent less than had been believed. The king was said to have remarked ruefully, “I have lost more to my astronomers than all my enemies.” But, a ship’s motion at sea was too great to make such precise observations.

While the Longitude Prizes languished, a Yorkshireman named John Harrison was building accurate pendulum clocks of wood — lignum vitae — which is minutely grained so it takes a fine polish and contains natural oils so the parts run on each other with virtually no wear. One Harrison clock has run with more than 102,000 daily windings since 1722.

Harrison became determined to solve the longitude problem. He knew that clocks at sea would have to remain reliable in frigid and torrid climates which would by contraction and expansion alter their pendulum length and thus timekeeping ability. He solved this problem by making his pendulum a grid of iron and brass, which expanded and contracted differently, enabling him to distort shape and thus keep the pendulum’s period constant. To compensate for the ship’s pitch and roll, he eventually developed, instead of a swinging pendulum, one coiled like a snail, a concept eventually incorporated into every spring in watches, alarm clocks and navigator’s chronometers through most of the 20th century.

After sea trials with several versions of increasing sophistication and compactness, Harrison’s “H-4” chronometer was complete and functional in 1759.

After delays instigated by Harrison’s rivals, (who still tried to calculate time from empirical observations of the heavens) one of these sailed on a vessel of the Royal Navy from Portsmouth in 1763. It was rowed ashore at Barbados in 1764 and formally opened to have its time checked and found well within the required limits. The longitude calculated using its readings was within a few miles of that “checked” using the laborious moons of Jupiter procedure.

Harrison had clearly won the prize, but delays from his detractors led him eventually to appeal directly to King George III. Harrison plead his case before the King , who sharing the inventor’s frustration announced: “By God, Harrison, I shall see you righted!” He was subsequently, in old age, awarded the money due him.

A Harrison chronometer sailed with Capt. William Bligh on one of his voyages, and in time, variants sailed on every substantial vessel in the world. Keeping time well resulted in knowing longitude reasonably well, and saved countless thousands of ships and no doubt hundreds of thousands of lives, enabling much of the world’s maritime trade, and in a real sense, the settling and success of the United States.

In the century just ended, electronic aids to navigation such as the radio direction finder, gyrocompass, radar, LORAN, and now, the extraordinarily successful and accurate Global Positioning System have greatly simplified navigation and given a certainty of position on the globe unprecedented in human history.

It’s when these systems fail that mariners must fall back … and should be trained and comfortable in doing so, on the old, tried-and-true measures of compass, chronometer, sextant and dead reckoning to manifest “the way-finding-art.”

Off the end of Long Island aboard Nimble, we were possibly tracing the homeward track Thorfin Karlsevni followed with no compass or chart. Amid the summer deluge, I plotted the last known position on our chart. I had our compass course and knew our speed, so every quarter hour, we “carried forward” our estimated, or “dead reckoning” position and marked it.

Connected with a line, this traced with some certainty our position as we closed with Montauk Point. Later, a momentary break in the rain revealed a glimpse of land dead ahead. We were aimed too far inshore. The fierce flooding tide which sweeps in toward Orient Point, to fill Block Island and Long Island Sounds had set us sideways toward the rocks. We corrected our course and carried forward the new line of position, again sailing in virtual blindness.

Suddenly, the last squall in this line had passed, and visibility opened to reveal the Point and its sentinel lighthouse, flashing reliably and welcoming. The surf beat on a beach of shingle rock, showing its white teeth and between us and the shore two giant ocean sunfish Mola mola, perhaps 300–400 pounds each, rolled in the long swells, their massive bodies visible through the waves and their huge fins alternately extended skyward, beckoning us around and to safety.

In half an hour we were in sheltered water and as the day’s last light faded, we anchored in a quiet bay, deeply carpeted with yardlong waving eelgrass.

The author is indebted to Capt. William S. Gates of the 17th century replica sailing vessel, Dove, for sharing his knowledge on historical navigational practices.