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Navigate using stars, wind and waves


TODAY, probably no one is afraid of falling over the edge of the earth. But that is exactly what some seafarers used to be afraid of and therefore stayed within sight of the country. Other brave sailors, however, overcame their fear and ventured out to sea.

The Phoenician seafarers, whose home ports were on the eastern edge of the Mediterranean, made trade trips to Europe and North Africa about 3,000 years ago. In the 4th century BC u. Z. a Greek explorer named Pytheas sailed around Britain and perhaps even reached Iceland. Long before European ships first sailed the Indian Ocean, Arab and Chinese sailors from the east had already crossed it. The first European to go to India by sea was Vasco da Gama. Interestingly, he reached his destination with the help of the Arab navigator Ibn Madjid, who showed Vasco da Gama’s ships the way during the 23-day crossing of the Indian Ocean. How did all these ancient navigators orient themselves on the sea?

The dead reckoning kept them alive

Ancient sailors had to rely on dead reckoning. As shown below, the navigator had to know three things: 1. his starting point, 2. the speed and 3. the course of his ship. The starting point was easy to determine. But how could the course be determined?

Christopher Columbus used a compass to determine his course in 1492. However, compasses were only available in Europe from the 12th century. Without a compass, the navigators turned to the sun and stars. When clouds obstructed the view, the sailors on the open sea orientated themselves on the long, even swell caused by steady winds. They watched closely how the direction of the swell was related to the rise and set of the sun and stars.

How did the seafarers determine their approximate speed? For example, they observed how long it took the ship to pass an object that had been thrown into the water at the bow. A more precise method, developed later, involved throwing a piece of wood overboard with a line with knots attached at regular intervals. The wood floating on the water pulled the line down from the moving ship. After a set time, the line was drawn in and the knots were counted. The result indicated the speed of the ship in knots (nautical miles per hour), a unit of measurement that is still used. If the navigator knew the speed, he could calculate the distance his ship covered in a day. Then he drew a line on a nautical chart showing how far he had come on his intended course.

Of course, cross winds and ocean currents could throw the ship off course. The navigator therefore regularly calculated and logged which corrections were necessary to keep the ship on course. Starting from his last entry, he made new calculations and measurements every day and recorded the results. When the ship finally dropped anchor, these daily entries on its nautical charts documented the route the ship had taken to its destination. More than 500 years ago, Christopher Columbus used dead reckoning to travel from Spain to North America and back. Thanks to his carefully kept nautical charts, today’s navigators can understand this remarkable journey.

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Navigation using the celestial bodies

How did the ancient navigators steer their ships with the help of the heavenly bodies? Sunrise and sunset indicated east and west. At daybreak, the navigators could see how far the sun had moved compared to the slowly fading stars. At night they determined their position using the North Pole, which is almost exactly over the North Pole in the dark. Further south, a bright constellation called the Southern Cross helped them determine the location of the South Pole. On a clear night, seafarers on all seas had at least one clue in the sky to check their course.

But these weren’t the only signposts in the starry sky. The Polynesians and other Pacific seafarers could read the night sky like a road map. One of their methods was to go to a star that they knew exactly would rise or set on the horizon in the direction of travel. During the night, these navigators also compared their course with the position of other stars. If their course was wrong, the heavenly bodies would help them correct it.

How reliable was this system? At a time when European seafarers mostly sailed close to land for fear of falling over the edge of a flat earth, seafarers in the Pacific apparently made long ocean voyages between relatively small islands. For example, Polynesians left the Marquesas Islands over 1,500 years ago and traveled north across the vast expanses of the Pacific. By the time they went ashore in Hawaii, they had covered about 4,000 kilometers! According to popular tradition of the islanders, the early Polynesians traveled from Hawaii to Tahiti and back. Some historians refer to these accounts as legends. But at least today’s seafarers have repeated this journey without navigation instruments, orienting themselves exclusively to the stars, the swell and other natural phenomena.

With wind power

Sailing ships were dependent on the favor of the winds. A ship made good progress with a tailwind, but headwind slowed it down significantly. When there was calm, the ship did not make any headway at all, which was not infrequent in the so-called Kalmengürtel – the region around the equator. Over time, the seafarers became familiar with the prevailing winds at sea and found shipping routes across the oceans. The navigators knew how to make good use of this winch.

Bad winds could, of course, mean suffering and death. For example, when Vasco da Gama wanted to sail from Portugal to India’s legendary Malabar coast in 1497, the prevailing winds first carried him far out to the South Atlantic and then back to the southeast and around Africa’s Cape of Good Hope. In the Indian Ocean, however, he encountered the monsoon winds that change direction with the seasons. The summer monsoon, which sets in early every year, arises in the southwestern part of the Indian Ocean and for months blows everything that is floating on the water towards Asia. In late autumn it is replaced by the winter monsoon. This blows with full force from the northeast back to Africa. Vasco da Gama returned from India in August and soon found himself in unfavorable winds. Instead of the 23 days in which he had crossed the Indian Ocean in an easterly direction, his return journey took almost 3 months. Due to the delay, fresh food became scarce and many sailors died of scurvy.

Experienced sailors who voyaged the Indian Ocean learned to watch both the calendar and the compass. Whoever wanted to sail east to India around the Cape of Good Hope had to leave in early summer at the latest or risk waiting months for a favorable wind. In order not to have to fight the summer monsoon for their part, the captains who wanted to sail from India to Europe did not allow their ships to leave until late autumn. The route across the Indian Ocean at that time can be imagined as a kind of one-way street with a changing direction of travel, as shipping traffic between Europe and the Indian Malabar coast often only ran in one direction.

Boat Navigation System
Boat Navigation System

Navigation today

Over time the art of navigation took a new course. Thanks to mechanical instruments, one was no longer so dependent on a keen eye and guesswork. The astrolabe, and later the more precise sextant – devices used to determine the height of the sun or a star above the horizon – enabled seafarers to calculate which latitude they were at north or south. Using the ship’s chronometer – a reliable, seaworthy watch – they were able to determine the longitude and thus their position in an easterly or westerly direction. These instruments were far more accurate than dead reckoning.

Today, gyro compasses without a magnetic needle show where north is. And the Global Positioning System helps you to determine your exact location with just a few push of a button. Electronic displays often replace paper charts. Yes, navigation has become an exact science. This technical progress certainly deepens our respect for the courage and skill of the seafarers of old, who, armed only with the knowledge of stars, wind and waves, crossed seemingly endless oceans.

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