Navigation of the American Explorers – 15th to 17th Centuries

Seventeenth century travelers to Maine’s coast such as Samuel Champlain, George Waymouth, and John Smith carried state-of-the-art navigation tools for both dead reckoningand celestial navigation.

Navigation Tools for Dead Reckoning and Piloting
Invented in China in the 3rd century BC, the compass did not come to Europe until the 12th century AD. By the time of Columbus’ voyage it was common. Instead of degrees, thecompass card, on which directions were drawn or printed, showed the points of the compass, including north, south, east, and west. There are 32 points of the compass, the four main quadrants of the circle each divided into eight 11¼ ° points. Columbus noticed that, as one sailed across the Atlantic Ocean, the variation between magnetic north and true north changed. On future trips he used this to predict, roughly, his arrival in America.

Dry Card Box Compass

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Points of the Compass

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A Chip Log, a Log Line Reel, and a Sand Glass

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The next most important tool was the chip log, introduced in the late 16th century to measure speed. The chip, a quarter circle of wood, was attached to a light line on a reel. Knots were tied at 47′ 3″ intervals, the distance the line would be pulled out in 28 seconds if the ship’s speed was one knot or nautical mile in an hour, when the chip was dropped overboard. With a 14- or 28-second sand glass, navigators could see how fast the vessel was going by counting how many knots rolled out before the sand glass expired. Before the chip log, navigators estimated speed by timing how long a chip of wood in the water would take to pass from bow to stern.

Traverse Board

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Compass and log helped navigators keep track of position. They used a lead line to determine water depth and bottom type. A heavy piece of lead at the end of a long marked line had a cavity in its bottom, which, when coated with grease or tallow, brought up a bottom sample. Experienced navigators often could determine position based on whether the bottom was muddy, sandy, pebbly, rocky, or covered with vegetation or shell fragments. Crossing the Atlantic, navigators used the lead line to find the continental shelf, and, more importantly, find the Grand Banks and other fishing grounds.

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Wright’s Chart of the World, 1599
To record a vessel’s courses and speeds, the navigator used a traverse board. The board had a line of holes radiating from the center towards each of the 32 compass points. Sailors inserted pegs in the holes to show the vessel’s course and speed each half hour. The navigator then used traverse tables to add these and give an average course for a four hour watch. This result then was entered into a logbook along with information about the weather, changes in sails, and items concerning the crew.

The Mariner’s Mirror 1588

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Guides for the Navigator
The seventeenth century navigator had little published information. Charts were rare; some advanced navigators carried globes. Mercator projection charts were far more useful than earlier charts. With its mathematical errors corrected by Edward Wright in 1599, the Mercator projection chart allowed mariners to draw a rhumb line between two points, get a bearing and sail that line.

The English Pilot, Fourth Book

pilot book

 

The earliest sailing directions originated in the Mediterranean as manuscripts called portolanos which were first printed in the second half of the sixteenth century. The first important collection was published in 1584 by the Dutch pilot Waghenaer. These volumes, with charts, sailing directions, navigational instructions, and tables, became known in England as “Waggoners” In 1671, the first of four volumes of The English Pilot appeared, based mostly on Dutch sources. These covered Europe, the Far East, and North America.

Seaman’s Quadrant

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Tools for Finding Latitude and Time
The only way navigators could estimate a vessel’slongitude was by dead reckoning and measuring variation. Celestial navigational instruments were designed to help find a vessel’s latitude, the approximate time, and the direction of true south.
The quadrant, the earliest device used to find latitude, was a quarter-circle of wood, marked in degrees, with a plumb line and a sight along one edge, first taken to sea around 1460. Another early latitude-measuring device is the astrolabe. It is a disc with degrees and a movable arm with sights, first known to be at sea about 1481.

Astrolabe Diagram

astrolabe

The Method of using an Astrolabe

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In the 15th century, Portuguese Prince Henry the Navigator pioneered nationally sponsored exploration and cartography. Portuguese navigators apparently took the cross staff to sea about 1515. It has two parts: a long graduated staff and a sliding crosspiece.

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Cross Staff reproduction

The Method of using a Cross Staff

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The navigator holds one end of the staff near his eye, where both the sun and horizon may be sighted, and then moves the crosspiece along the staff until one end is lined up with the horizon and the other with the sun or star. The angle is read from the scale on the staff. The cross staff required the navigator to look directly into the sun, almost impossible in bright sunlight. But it could be used when the ship was moving, and it was simple and relatively inexpensive.

Backstaff reproduction

The Method of using a Backstaff

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Nocturnal, George Waymouth

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A variation of the cross staff is the backstaff, invented byJohn Davis about 1594 and published in his Seaman’s Secretsin 1595. With it a navigator could measure angles accurately without looking directly at the sun.
The backstaff, in its final form, was made of wood and was made up of two arcs, a larger 30° arc and a smaller 60° arc.Vanes allowed accurate sighting of the horizon, while the sun showed a shadow on another vane. Also called a Davis quadrant, it could only be used for sun sights.
At night, navigators could tell time using a nocturnal, a device that measured the angle from the North Star to the pointer stars, either in Ursa Major (the Big Dipper or Big Bear) or in Ursa Minor (the Little Dipper or the Little Bear). It used the vertical as a reference, and required the month and date to be set. A sundial could be used in daylight.

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Gunter’s Scale (detail)
By the middle of the 17th century, thanks to the invention of logarithms by John Napier which were transformed into a simple calculator by Edmund Gunter, navigators with little mathematical training could solve trigonometric navigational problems.
By the end of the seventeenth century, navigators were able to tell time within a quarter of an hour and find their latitude within a few miles. Despite their relatively simple instruments, these mariners sailed the globe.

Source : penobscotmarinemuseum.org/

 

 

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History of Navigation: Introduction

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Navigation is finding one’s way at sea and in the air. Without roads, the navigator relies on coastal, celestial and electronic marks. The word navigate comes from the Latin words for ship (navis) and “to drive or guide” (agere).

Navigation is both art and science and requires understanding of the earth and heavens. Changes in navigation science and technology over the last five hundred years have altered the navigator’s work and methods. Yet, the navigator’s basic task remains constant: to keep track of where the ship has been and where it is now, and to plan where the ship will go next.

Navigation is based on astronomy, physics, oceanography, meteorology, earth sciences, aerodynamics, and hydrodynamics. Mathematics can include arithmetic, algebra, trigonometry, logarithms, geometry, and analysis. The navigator needs practical judgment to make good decisions with incomplete or overly complex data.

While today’s electronics have helped automate navigation, they also provide much more information for the navigator to process, and the navigator has to be prepared for electronic failure. The work of navigation requires care, but it is fascinating in that it combines so many disciplines, and requires forethought and planning.

Early Astronomers

Ptolemy

Ptolemy, Claudius

c.90-168. Probably born in Egypt of Greek heritage. Mathematician, astronomer and cartographer. With simple projections he created a world map that summarized geographic information of the Greco-Roman world. He created a latitude/longitude system to describe locations. He conceived a world or heliocentric model of the Universe to explain celestial motions, drawing on the work of Greek and Babylonian astronomers. Both of these served for practical navigation until the 15th century.

 

copernicus

Copernicus, Nicholas

1473-1543. Polish astronomer and mathematician who developed and published the view of an earth that orbited a stationary sun. His book De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres) was printed just before his death.

kepler

Kepler, Johannes

1571-1630. German astronomer and mathematician who theorized that planets and the Earth travel around the sun in elliptical orbits. He published his theory in 1609. Using his theory, he was able to calculate precise predictive tables for planetary motion.

Galileo

Galilei, Galileo

1564-1642. Italian mathematician, astronomer and instrument maker. In 1609, basing his work on a description of a Dutch telescope, he developed the first practical telescope which he used to discover the moons of Jupiter the following year. This tool was an astronomical breakthrough, for no longer were astronomers dependent on their eyes alone for observation.

newton
Newton, Sir Isaac

1643- 1727. English mathematician who laid the groundwork for calculus and did breakthrough work in optics and gravitation. In 1687, he published his Principia Mathematica in which he applied his laws of motion to the motion of celestial bodies, providing the mathematics to prove Kepler’s theories. These would be used by future astronomers to produce navigational tables. He also developed the universal law of gravitation.

aristotle

Aristotle

He is sometimes called the grandfather of science. He studied under the great philosopher Plato and later started his own school, the Lyceum at Athens. He, too, believed in a geocentric Universe and that the planets and stars were perfect spheres though Earth itself was not. He further thought that the movements of the planets and stars must be circular since they were perfect and if the motions were circular, then they could go on forever. Today, we know that none of this is the case, but Aristotle was so respected that these wrong answers were taught for a very long time. Aristotle, outside of astronomy, was a champion observer. He was one of the first to study plants, animals, and people in a scientific way, and he did believe in experimenting whenever possible and developed logical ways of thinking. This is a critical legacy for all the scientists who followed after him.

Source: penobscotmarinemuseum.org