Medieval Navigation in the Arabian Sea

Read First: Longitude Zero

Indians call the bay between Africa and India the Arabian Sea. Throughout the medieval times it was controlled by Arab sailors. They established settlements down the East coast of Africa, as far down as Malindi in Kenya. All traders from this Islamic world, whatever their ethnicity or religion, were called Arabs in India. I will continue this practice in this article.

They also had allies among the many Indian principalities along the West Coast: not only the Indian Muslims but also the Eastern Orthodox Christians, Jews, Nairs and many of the Kings such as the Zamorin of Kalikut ( Kozhikode Samoothiri in Malayalam). Being middle men in the spice trade made many Arab principalities immensely wealthy. This cozy arrangement was upset by the arrival of Vasco da Gama in 1498. Although the Portuguese were backward technically and economically, they had one important argument in their favor: cannons. In a series of wars they broke the Arab monopoly and opened up direct trade between Europe and India.

The European navigational methods were developed in the Northern Latitudes of the Atlantic. They relied mostly on the position of the Sun. Arabs mainly used stars to determine their position. These methods, while crude by modern standards, where good enough to take them even past the Arabian Sea to the Bay of Bengal and farther East, as far as Korea. It does not appear to have taken them around the Southern Cape of Africa until some Arab sailors hitched a ride on European ships.

Much of this navigational knowledge was handed down orally from Mu’allim (Master or Captain) to student (often son) over generations. It was a practical art, although some navigational theory lay behind it. To preserve the monopoly of the Sea, it was important these trade secrets did not get into the wrong hands, especially the hated Franks, as the Europeans were generally known5. Or even worse, the Ottomans.

Ahmed bin Majid al-Najdi

The definitive text on Arab Navigation was by Ahmad bin Majid: Kitab Al-Fawaid Fi Usul Al-Bahr Wal-Qawaid of Ahmad B. Majid Al-Najdi, translated by G. R. Tibbetts6 as Arab Navigation in the Indian Ocean before the Coming of the Portuguese . In order to be memorised easily, the work is written as poems.

His literary style, if it may be called a style, seems to be the very much the unpolished work of a literary amateur.

says Tibbetts, who ought to know. In addition to his navigational treatise, Majid is also known for some other poems, including lamentations about the arrival of the Portuguese. However, the accusation that he was the navigator who betrayed the secrets of the trade to Vasco da Gama is refuted by Tibbetts. Most likely an Ottoman writer was spreading that story to malign Majid’s good name, and by extension, that of the Arabs.But Ibn Majid could have been responsible indirectly: the pilot that da Gama hired (most likely a Gujerati Muslim) could have learned his craft from Majid’s poems.

At low latitudes close to the equator, the angle the Pole Star is above the horizon is fairly easy to determine at night. It is a good approximation to the latitude. Because of the precession of the Earth’s axis, the Pole Star is not located exactly due North. Five hundred years ago this effect was larger than it is now (it will be zero in two hundred years) and the Arab navigators (Mu’allim) learned to make a correction for it7. The basic ideas is to imagine that the Pole Star ( like all stars) goes around a circle centered at True North, once each day. The radius of this circle is smallest for the Pole Star as it is closest to True North.

If the Pole Star is obscured or invisible as in the Southern Hemisphere, the latitude could still be gleaned from the position of the other stars although with greater difficulty. This was supplemented by the compass bearing (majra). Natural phenomena on the ocean ( currents, presence of Sea snakes) were used as additional pieces of information to confirm the route.

The Kamal

How was the angular position of the Pole Star measured? Using a simple device, called a Kamal: a string tied to a square piece of wood. The bottom of the square is aligned with the horizon; the top with the Pole Star. The distance along the string, one end held between the teeth, then gives the latitude. There would be knots tied to the string to record the latitudes of the standard destination cities. Within th Arabian Sea, as long as you proceed East (or West for the return trip) on the latitude of the city you have a good chance of getting there. You would also have at hand a rough knowledge of the distance, in terms of the number of sailing says. These ways memorized as poems, as from the Fawa’id. The compass will help you hold a steady bearing. In addition, the sailors knew that the open ocean was not without recognizable features. An entire chapter of the Fawa’id is about species of sea snakes and how they can help you know which coast you are approaching.

The Longitude Problem

If you have an accurate chronometer which works on a ship at sea, determining longitude is simple. You set it to the time at your favorite sea port whose longitude is known ( perhaps even the prime meridian in your system passes through there). The time when the Sun is directly overhead will give you the longitude. The example that Aryabhata gives illustrates the method: when it is noon at Lanka (the imaginary point where the prime meridian meets the Equator) it will be six o’clock in the evening at 90E longitude and six in the morning at 90W. The problem is that a pendulum clock does not work well in a ship at Sea. The European solution to this problem was to invent an accurate chronometer, one of the most fascinating stories of the Age of Exploration8 .

It is possible to determine the longitude by more complicated calculations from positions of celestial bodies. As we saw earlier, the whole problem is to determine the time as measured at some home port of known longitude. Tables of positions of stars and the moon at each hour of the year can be prepared by the home port. The US Naval observatory9 and Her Majesty’s Nautical Almanack Office still publish these. Because of the rotation of the Earth, the actual positions will depend on the time of observation at any point on the Earth. But, the difference in positions of the moon (or other moving celestial body like Jupiter) and a fixed star (usually chosen to be Aries) is independent of the position of observation: knowing that you can look up at the time at the home port in the Almanack. It is not impossible that some version of this scheme was used by the Arab astronomer/navigators or by their Chola contemperories.

Longitude in the Faw’aid

But there is no mention of it in Ibn Majid’s book. He ridicules some methods for determination of the longitude used by some other navigators that he says are wrong. Tibbetts actually says that the medieval Arab Navigators had no way of determining longitude. There is no mention of a prime meridian nor were any accurate chronometers available. But his statement on page 355:

Without any accurate method for measuring time over long periods, longitude cannot be measured..

is incorrect as we explained earlier. It is true that star positions can only determined crudely with the kind of observations made on a ship, but then the latitude was determined also using these very same crude methods. Could it be that Majid either was not the greatest navigator of his time as he proclaims, or that he didn’t give away all of the trade secrets in his poems?

As we noted earlier, you could get by without knowing the longitude in the Arabian Sea, which is basically a large bay. If you know the latitude of the destination, and sail East-West holding a steady latitude will take you there; Arab ships had the lateen sail which allowed them to sail much closer to the wind than European ships of the time: so if the wind was in more or less the right direction you can hold a steady course.

But how could the Arab sailors have gone past India to Sumatra, as far as Korea? How could they have navigated to islands in the Southern Indian Ocean? Majid mentions Chola navigators as the experts in sailing the Eastern ocean. What methods did the Chola use? Can anyone help?

The state of our knowledge is unsatisfactory. The most well-known book on Medieval Arab Navigation does not give any method for determining longitude. So it still is not clear whether Kalikut being on the Indian prime meridian has any special significance.

5. `Firengi’ is still used as a derogatory term for white foreigners in many Indian languages. The Firengis of Star Trek:the Next Generation, like the bar tender Quark, are a caricature of this stereotype of the avaricious Western trader.

6. Arab Navigation in the Indian Ocean before the Portuguese
by G. R. Tibbetts, RoutledgeCurzon(2002)ISBN-10: 0947593233

7. Medieval Arab navigation on the Indian Ocean: Latitude Determinations
Alfred Clark Journal of the American Oriental Society, Vol. 113, No. 3 (Jul. – Sep., 1993), pp. 360-373

8. Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Timw
by Dava Sobel, Penguin (1996), ISBN-10: 0140258795.


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