Above painting: Louis Jean Francois - Mars and Venus an Allegory of Peace
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Tuesday, June 12, 2018

Navigation During the Age of Sail

Back in the days of sail, seamen didn’t have the state of the art satellite-based navigational systems, also known as global position systems (GPS), to cross the seas. They relied on mariner knowledge, the horizon, the stars, the currents, and nautical instruments to help plot their courses and guide them on their journeys.

Here is an alphabetical list of some of those tools. 

Astrolabe - ancient inclinometer which calculates the altitude of the sun and stars to determine
Astrolabe, cross staff, and sextant
latitude. Elaborate astrolabes have etchings of how the sky looks at any given time or season. Moving components to what the user sees will tell them their location, as well as the date and time. For sailors, the astrolabe was a much simpler graduated ring with an alidade and often made of brass for longevity at sea.

Backstaff - users of this instrument have their backs to the sun and marks the angle of the sun by measuring its shadow with the help of three vanes—horizon vane, sight vane, and shadow vane.

Compass - one of the oldest nautical tools is comprised of a magnetic lodestone which uses the earth’s magnetic field. The compass, showing the cardinal directions (north, south, east, west), always points north. Handy when there is nothing on the horizon but water and more water.

Lead line
Chronometer - a timepiece used to establish longitude and/or an exact measurement of time that evolved from counter-oscillating beams and springs to a beating balance wheel.

Cross staff - the basic predecessor of the backstaff to determine latitude.  Users faced the sun, or Polaris (the North Star), to measure its angle to the horizon by sliding a cross piece up and down the main staff marked with measurements.

Lead line - a long rope with a lead weight at the end and knotted at various lengths used to measure depth. The lead weight also had a hollowed bottom filled with tallow or animal fat. This sticky substance would bring up the make-up of the seabed (sandy, rocky, clay, shells, pebbles) providing important information on anchoring or piloting a ship.

Nocturnal
Log line - a long rope on a spool with a board (log) at the end used to measure a vessel’s speed. Knots were tied along the rope at six feet intervals. Six feet equaled one fathom. When the log line is thrown overboard, the number of knots passing over the railing in thirty seconds were counted, thus giving the sailors a rough estimate of how fast they were going in knots—the nautical measurement much like how fast a car goes in miles per hour.

Nocturnal - based on the time of year to ascertain the time of night using the location of the stars such as Polaris, Ursa Minor, and Ursa Major. It uses a set of dials—months, hours, and the location of stars—and has a pointer. Important when calculating tides.

Quadrant - measures at 90o angles how high the sun or Polaris is above the horizon. To use, sight in on the right side of the edge of the angle. The plumb bob (a weight tied to a rope) will cross the scale along the bottom to give the angular height of the celestial body.

Traverse board
Reflecting circle - a circular instrument which uses mirrors to measure the angular distance between two diverging objects sat once. Mostly used for finding longitude.

Sextant - measures the angle between a celestial object and the horizon to determine latitudes and longitudes. This instrument, which can be used day or night, is the culmination of its navigational predecessors and, due to its precision, has been used well into the twentieth century.

Telescope - also called a spyglass or “bring ’em near”, an optical tool that uses lenses or mirrors to make distance object appear closer

Traverse board - a wooden board with holes and pegs used to record the ship’s speed and direction during a given watch (the shift which crewmen worked). At the end of each watch, the navigator collected the information and figure up the vessel’s progress and projected track.

All these instruments aided mariners in creating one of their most valued navigational tools, their sea charts. Daunting, isn't it? Thank goodness for today's GPS.

About the Author                                                


Jennifer is the award-winning author of the Romancing the Pirate series. Visit her at www.jbrayweber.com or join her mailing list for sneak peeks, excerpts, and giveaways.

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