The voyage of the Kon-Tiki was the idea of Thor Heyerdahl, a Norwegian geographer and zoologist. He had an unusual theory about how the Polynesians came to inhabit their islands. He was doing research of the origins of the island's animal life in the 1940s and realized that many of the plants came from places an ocean away; the current ran from east to west and many plants were similar to those in South America. Even though most scientists thought Polynesia was populated by people from Asia, he was convinced otherwise. He though that Peruvians had migrated to Polynesia in ancient times and were the ancestors of modern Polynesians.
One of the reasons most scientists cited against Heyerdal was that South Americans didn't have the right kind of boats to make it to Polynesia in the first place. Heyerdahl set out to prove them wrong and build a raft made of balsa that was known to be similar to those used by ancient Peruvians. The raft was made of 9 two-foot thick balsa wood logs which were between 30 and 45 feet. The longest logs were put in the middle and were lashed to cross beams. This was covered by a bamboo deck with an open hut on it. It had a bipod mast with a square sail, five centerboards, and a steering oar.
He called the raft the Kon-Tiki and left from Peru to go to Polynesia in 1947. Most historicists of the time were sure he would fail because the boat would never make it through the ocean for the 4300 mile trip. Thor Heyerdahl and five others departed from Callio, Peru and went 4300 miles (8000 kilometers) to Polynesia (Raroia atoll, Tuamotu Archipelago). The boat did not fail because they found that the logs acted almost as a sieve which let excess water through. They also found a way to steer with the center board which allowed to them to approach the wind at close to a 90 degree angle. It took them 101 days to complete the trip.
The success of Thor Heyerdahl's expedition proved that ancient South Americans could have originally colonized Polynesia. The trip had attracted worldwide interest and the book he wrote about the trip (called simply "Kon-Tiki") has been translated into 67 languages and has sold more than 20 million copies. He had also been provided with a film camera before the trip began. He taped everything from the building of the raft up until the actual arrival to the islands. His black and white movie was presented in 1952 and won an Oscar for most outstanding documentary. The Kon-Tiki raft is now located in the Kon-Tiki Museum in Oslo, Norway which is visited by hundreds of thousands of interested people every year.
Sources:
http://www.jewelersweb.com/tahiti/history2.htm
http://www.bradshawfoundation.com/thor/
http://www.plu.edu/~ryandp/thor.html
http://www.museumsnett.no/kon-tiki/Expeditions/