WHEN 15th century Portuguese explorer Vasco da Gama sailed to India, he got stuck on Africa's east coast and had to seek the help of a Gujarati navigator to cross the Indian Ocean.

According to Varadarajan, as early as the Rig Vedic period (circa 2500 BC), there are references to a knowledge of the sea and of navigation. Traditional navigation is not dependent on instruments -- except for simple gadgets like the kamal (astrolabe) -- and is based on a thorough knowledge of the wind, waves, tides, currents and astronomy.

Says Arunachalam, "The traditional system of navigation is an art based on a cumulative package of craft wisdom, rich sea experience, a well-cultivated sense of the environment, perception and judgement."

A good example of this is the way the seafarers of Tamil Nadu use the wind. Says Victor Rajamanickam of Thanjavur's Tamil University, "The sailors consider the wind to be not only a source of energy but also a guide to destinations and good fish catches and an indicator of weather change."

The mariners classify winds into eight categories, according to direction and location (See chart). Says Rajamanickam, "Some winds are ideal for navigation and others are useful for predicting rainfall and cyclones. When in distress, the sailors are adept at deciphering the wind to guide them to shore."

The sailors also harness as much wind energy as possible. Rajamanickam found a 300-tonne Tuticorin boat with 27 different types of sails that was able to attain an average speed of 25 nautical miles an hour. Similarly, the sailors have an amazing knowledge of the waves, which are used to both determine direction and to predict cyclones.

The tides, stars and the planets are all important navigational aids. As instruments, even the outstretched hand can be used to measure the altitude of a star (See figure). Anchors made of stone, wood or iron and knotted ropes are used to measure depth.