The original caravel of the 15th century was a type of fishing vessel with Lateen sails (triangular sails supported by a beam at the top), which made them extremely manoeuvrable. The design proved so successful that Henry the Navigator used it as the basis for his designs of ships for exploratory voyages.
Photo: Caravel Boa Esperança of Portugal; public domain (Brazilian Navy)
Lateen sails were more difficult to handle than square sails but allowed caravels to sail close to the wind when required. They were not practical for long voyages of exploration, when the ships would follow the prevailing winds for lengthy periods of time. For such voyages a caravel would be re-rigged with square sails and became what was called a "caravel redunda." To spread the square sails over the length of the vessel and allow them to catch more wind one of the shorter masts was often moved to the forecastle (front) of the ship;
Photo: Caravel Redunda Espírito Santo of Brazil; public domain (Brazilian Navy)
Christopher Columbus' ship Santa Maria was a caravel redunda. She was much slower than his second ship, the caravel Niña, and very unpopular with the crew. But her sails were found to be more easily handled than the lateen rigs of the Niña, so on the way to America the Niña was converted into a caravel redunda at the Canary Islands.
Classic sailing ships. http://website.lineone.net/~dee.ord/ships.htm (accessed 28 December 2003)