("Balsa" was the common South American term for raft, the term also being applied to rafts of reed and of hollow gourds. Balsa wood, it appears, was so named because it was "raft wood.")
The "hulls" of these ocean-going rafts were substantial. They always consisted of an odd number of logs, and often had some degree of taper. Sometimes it was just the central log that extended forward of all the others; at other times, each log was shorter than the one inboard of it, so that the entire bow had a stepped wedge shape. In some cases, the stern was step-wedge shaped as well.
Above the hull's main logs were several cross-pieces of diameter roughly equal to the main logs, the whole being lashed together with rope. Then above the cross-pieces, there was plank decking and often a house of two or even three decks. In the lowest compartment would be stored anchor rocks and water containers. The second level was crew quarters. The top level was for cargo that needed to be kept dry. The height of the decks in the house was only about four feet. The whole hull structure weighed so much that, laden, the main logs would often "float" two or three feet beneath the surface.
|a. Balsa raft recorded by Admiral Paris, 1841. Length about 30 meters; beam 8-10 meters. Note tapered hull shape, multiple daggerboards, deckhouse, and squaresail on bipod mast. Click this or any image for a larger view.|
At one time, anthropologists and historians disputed whether aboriginal South Americans had sails on their rafts prior to European contact, but this question seems to have been pretty soundly answered, as sailing rafts were recorded by Europeans within just a few years of first contact, and it seems highly unlikely that sails would have been adopted so quickly. Furthermore, the method of steering was one unknown to Europeans at that time, and if the sail had been adopted from them, it seems certain that the rudder would have been as well.
Instead of a rudder, South American sailing rafts were steered by multiple daggerboards (incorrectly called either "centerboards" or "leeboards" in my sources). There were typically three or more; aft, athwart of the mast, and forward. By selectively raising or lowering the boards fully or partially between the hull logs, the underwater center of resistance could be changed.
Assuming that the sail's center of effort remained fixed, one would turn upwind by lowering the forward boards and raising the aft ones. This would allow the stern of the raft to blow downwind, while the deployed boards forward would allow the bow to resist doing so, leaving the bow pointing more into the wind than the stern. To turn downwind, one would raise the forward boards and lower the aft ones.
Once it was settled in the Indians' favor that they did indeed have sails, the next question in dispute was the nature of the sail: square or triangular. Both had been noted (not always unambiguously) by Europeans within a couple hundred years of first contact, but it appears that the triangular sail was the aboriginal design, and that this was displaced by the square sail fairly soon after European contact. Although variations were noted, the aboriginal rig seems to have been comparable the Oceanic sprit rigs of the Pacific – which can lead to all sorts of unprofitable arguments (which I'll avoid) about the diffusion of technology eastward or westward across the Pacific.
The later square sail was typically set on a pair of shears, or a bipod mast, as shown. With the triangular sail probably being the more weatherly one, the reason for the switch to the square sail is a mystery. Eventually, the squaresail and bipod mast were replaced by the handier and more weatherly European-style lugsail hoisted on a single mast. But even with the adoption of the European-style sails, daggerboard steering remained the norm.
|b. An image from 1619, showing crew manipulating three daggerboards; two masts with triangular sails, anchor stones on foredeck. Note the curved masts are two-part, and the sails have no boom or lower sprit.|
|c. Guayaquil raft in 1748; much smaller than Admiral Paris's raft. Details of the rig include the shears or bipod mast, backstays, what may be a forestay, and a bowsprit-like spar that serves as a bowline.|
(Sources: The Sea-Craft of Prehistory, Paul Johnstone; Aboriginal Watercraft on the Pacific Coast of South America, Clinton R. Edwards)
(Images: a. from Johnstone; b, c. from Edwards)