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

compass
Points of the Compass

pointer

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

etc

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

traverse

 

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.

wright

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

guide

 

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

qudrnt

 

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

how

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.

cross

Cross Staff reproduction

The Method of using a Cross Staff

how3

 

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

how2

Nocturnal, George Waymouth

nocturnal

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.

stick
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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