The Incas used guaras, or centreboards, which they thrust down between the logs, and working with sails, could more effectively tack into the wind than any European ships. Since the guaras function in the currents as sails do in the wind they are essentially sea current sails. By the guara technique a skilled crew could sail a balsa raft in any wind or current to any part of the Pacific. The importance of centreboard sailing was unknown to European boat builders until the late nineteenth century and not understood by scholars until Thor Heyerdahls 1952 presentation of Guara Sailing Techniques Indigenous to South America. Even then few scholars trusted Heyerdahls work.
From Atlantis in America Navigators of the Ancient World by Ivar Zapp and George Ericson