The Kon-Tiki carried five planks of fir, an inch thick, two feet wide and six feet long, pushed down on edge into the chinks between her logs and held with wedges and ropes. Heyerdahl’s book calls them centreboards and says they were “scattered about without system”. The Spanish chroniclers of Peru had called them guaras, and the fullest account of what they were for had been in print, in English, since 1758. This piece sets that account beside what the crew of 1947 discovered, and what they did with the discovery.

Guayaquil, 1748

Jorge Juan and Antonio de Ulloa were two young officers of the Spanish navy sent in 1735 to accompany the French academicians who were measuring a degree of the meridian at Quito. Their Relación histórica del viage a la América Meridional was published at Madrid in 1748, and an English translation, A Voyage to South-America, appeared in London in 1758. In Book IV, chapter IX, describing the river and coast of Guayaquil in what is now Ecuador, they turn from the houses to the vessels, “which, omitting the Chatas and canoes as common, are called Balzas, i. e. rafts, a name which sufficiently explains their construction, but not the method of managing them, which these Indians, strangers to the arts and sciences, have learned from necessity.”

The rafts, they wrote, were made of “five, seven, or nine beams” of balsa, “a whitish, soft wood, and so very light, that a boy can easily carry a log of it three or four yards in length and a foot in diameter.” The beams were lashed with bejucos, lianas, and the thickest was laid in the middle, “and thence the number of beams is always odd.” The larger rafts carried “between four and five hundred quintals, without being damaged by the proximity of the water; for the waves of the sea never run over the Balza; neither does the water splash up between the beams, the Balza always following the motion of the water.” Instead of a mast the sail was hoisted “on two posts or sheers of mangrove wood”. The nine logs, the odd number, the long middle log, the mangrove sheers: it is the Kon-Tiki, two centuries early.

Then comes the passage that Heyerdahl’s 1950 paper cites in a footnote and does not quote. It is given here in full from the 1758 edition, pages 197 and 198:

“Hitherto we have only mentioned the construction and the uses they are applied to; but the greatest singularity of this floating vehicle is, that it sails, tacks, and works as well in contrary winds, as ships with a keel, and makes very little lee-way. This advantage it derives from another method of steering than by a rudder; namely, by some boards, three or four yards in length and half a yard in breadth, called Guaras, which are placed vertically both in the head and stern between the main beams, and by thrusting some of these deep in the water, and raising others, they bear away, luff up, tack, lay to, and perform all the other motions of a regular ship. An invention hitherto unknown to the most intelligent nations of Europe, and of which even the Indians know only the mechanism, their uncultivated minds having never examined into the rationale of it. Had this method of steering been sooner known in Europe, it would have alleviated the distress of many a shipwreck, by saving numbers of valuable lives; as in the year 1730, the Genovesa, one of his majesty’s frigates, being lost on the Vibora, the ship’s company made a raft; but committing themselves to the waves, without any means of directing their course, they only added some melancholy minutes to the term of their existence. Such affecting instances induced me to explain the reason and foundation of this method of steering, in order to render it of use in such calamitous junctures; and that I may perform it with the greater accuracy, I shall make use of a short memoir drawn up by Don George Juan.”

Juan’s memoir begins with the theory of sailing as the textbooks of the day gave it, Renau, Bernoulli and Pitot, and then applies it:

“Whence it follows, that a Guara being shoved down in the fore-part of the vessel, must make her luff up; and by taking it out, she will bear up or fall off. Likewise on a Guara’s being shoved down at the stern, she will bear up, and by taking it out of the water, the balza will luff, or keep nearer to the wind. Such is the method used by the Indians in steering the Balzas, and sometimes they use five or six Guaras, to prevent the Balza from making lee-way, it being evident that the more there are under water, the greater resistance the side of the vessel meets with; the Guaras performing the office of lee-boards, used in small vessels. The method of steering by these Guaras is so easy and simple, that when once the Balza is put in her proper course, one only is made use of, raising, or lowering it as accidents require, and thus the Balza is always kept in her intended direction.”

Two things in this are worth holding on to. The boards do two jobs: together, as leeboards, they stop the raft sliding sideways; singly, raised or lowered at bow or stern, they steer her. And the claim is not that the rafts could hold a course downwind. It is that they could sail “in contrary winds”, tack, and lie to.

Mid-Pacific, 1947

The crew of the Kon-Tiki knew the first job and not the second. Heyerdahl’s book says that the boards “served as tiny parallel keels or centreboards”, put in “to prevent the flat wooden rafts from drifting sideways with wind and sea”, and that the Spaniards’ statement that the Indians had “steered” with them “sounded incomprehensible both to us and to all who had occupied themselves with the problem”, since a board jammed in a chink could not be turned like a rudder. The raft was steered with a long oar of mangrove on tholepins astern, the kind, Heyerdahl wrote in 1950, “still seen on native balsa-rafts in Ecuador”, and the man at the oar was lashed to the raft in heavy seas.

The discovery came by accident, well past the middle of the ocean. One of the five boards had broken loose and slipped under the raft. Watzinger and Haugland dived under her together and recovered it. The wind was steady and the raft had held her course for two days with the oar lashed; they pushed the recovered board down into a chink aft, and the Kon-Tiki altered course at once from west towards north-west and held it. Pulled up, she swung back. Pulled halfway up, she swung halfway back. Heyerdahl’s explanation is Juan’s, arrived at from the other end: the pressure of the wind on the sail made the mast the fixed point of a balance whose two arms were the raft forward and the raft aft; more board surface aft, and the stern held while the bow fell off before the wind; more forward, and the bow held. Boards nearest the mast had least effect. With the wind dead astern the boards did nothing, and the oar had to be worked all the time.

Then the sentence on which this entry turns: “We could certainly have continued our voyage by making the steersman stand and pull a centreboard up and down in a chink instead of hauling sidewise on the ropes of the steering oar, but we had now grown so accustomed to the steering oar that we just set a general course with the centreboards and preferred to steer with the oar.”

The storms of late July burst the lashings on all five boards. After that they hung loose, and the crew could not dive to re-lash them because of the sharks. On the morning of 7 August, drifting sideways on to the Raroia reef, Heyerdahl wrote that “with fixed centreboards we should still have had some hope of steering clear”; the boards were cut away before the raft went over the reef, so that she would wash across rather than catch.

What was and was not tested

The Geographical Journal paper of 1950 states the result without the story: “We found however that by simply raising and lowering one or more centre-boards behind or in front of the double-mast, the raft would immediately alter course, making the clumsy steering-oar unnecessary.” It also states the limit, in the sentence that closes the account of the voyage: “A primitive craft capable of drifting westward to an island 4300 miles away, was unable to push eastward to a neighbouring island within sight.” The footnote attached to it is the honest part: “This conclusion is based on our own experience. It may be that the early raftmen used the sails and centre-boards in other ways and attained a larger freedom of navigation. This is suggested in the narratives of Juan and Ulloa.”

In his reply to Heine-Geldern in March 1951 Heyerdahl was plainer still: “Our raft was undermanned for paddling and its crew had never seen one before, nor a guara (centre-board).”

What the raft tested, then, was whether balsa logs lashed with rope would carry six landsmen downwind across the Pacific. They would. What it did not test was the one capability that Juan and Ulloa had actually recorded, and that would matter most to anyone asking whether the rafts of Ecuador and Peru were ships or driftwood: whether, with a crew who knew the boards, a raft could be sailed across the wind, or back against it. The Kon-Tiki could not go back to an island she could see. The rafts of Guayaquil, by the account of two naval officers who had watched them, could tack. Heyerdahl went back to the question later; a paper of his on guara navigation appeared in the Southwestern Journal of Anthropology in 1957, and it has not been read for this entry. In 1947 the boards went across the Pacific as ballast against leeway, were understood for an afternoon, and went over the reef as splinters.

Sources

• George Juan and Antonio de Ulloa, A Voyage to South-America, translated from the Spanish (London, 1758), vol. 1, Book IV, chapter IX, pp. 195–198, read on the page images. archive.org
• Thor Heyerdahl, The Kon-Tiki Expedition: By Raft across the South Seas (George Allen and Unwin, London, 1950), the chapters on building the raft and on the halfway discovery. In copyright; quoted briefly. archive.org
• Thor Heyerdahl, “The Voyage of the Raft Kon-Tiki,” The Geographical Journal 115 (1950), pp. 20–41, at pp. 25, 28 and 30; and “Voyaging Distance and Voyaging Time in Pacific Migration,” The Geographical Journal 117 (1951), pp. 69–77, at p. 71. 1950, 1951
• Thor Heyerdahl, “Guara Navigation: Indigenous Sailing off the Andean Coast,” Southwestern Journal of Anthropology 13 (1957), pp. 134–143; cited for its existence, not read. doi.org