Raft Navigation on an Ocean
There is a difference between maritime ethnology as Heyerdahl cultivated - and maritime archaeology investigations as they did at the centers in Roskilde. More or less the difference is: A): ethnology: what could they - and B): archaeology: how did they?
What Thor Heyerdahl did was the ethnological part, and with Kon-Tiki he largely demonstrated, that a balsa raft could cross an ocean.
Heyerdahl verified that it was possible for the South Americans to reach the islands in the Pacific Ocean. He didn't show how they could return to South America by balsa raft, and until today nobody have demonstrated that.
Sail ships in historical time with their compass or astrolabe have always been able to find their way back. With charts and GPS is no problem at all, so to day we can't call it a challenge in navigation to sail out and get home with any craft - neither with a raft-craft. Therefor to locate an Easter Island behind the horizon will be no technical problem - a sea-scout with GPS can do it in his dinghy.
Nevertheless now 70 years after the deed of Thor Heyerdahl, 20 replica rafts have sailed out, but no raft sailor has returned to his port of departure. Until now no raft sailor has been able to repeat the old trade route along the coast to Mexico - even if we have seen attempts. No raft-sailor has tried to follow the wake of the many rafts of the Inca Tupac Yupanki fleet to Mangareve Islands and Rapa Nui and then return to South America. And even if the Ecuadoreans do it every day in the still active raft society of Guyaquil, no actual scholar nor any official expedition has been able to beat against the wind with a Guara-steered raft.
That is the sad fact, and what we want to know about.
Only very few post Heyerdahl balsa rafts were sailing out with any archaeological purpose
Stemhead of Tangaroa-2 2008
Of the 20 raft replicas as have sailed out 12 was lost. Of those twelve the six was lost due to attack by the clam Teredo Navalis.
A loss-rate over 60% no maritime culture will accept neither then nor now. No Inca sovereign would sail out with his army with a threat to loss 60%.
Conclusion: We miss something.
Classification of what we would like to know more about:
The little we can expect of documentations and writings
We in the Western World are perhaps gazing too much on own navel. The naked truth is, that we don't know much about history of those civilizations as have developed their writing system on base of sylabtic, logographic or iconic nature, as are far outside the principles in latin letters. Quipus with their colored knots on yarns even worse.
Even foreign language with letters of Gothic or Cyrillic shapes, as are very comparable with the latin alphabet, make many erudites stop up and dismiss. The scholars act as they prefer to work within own language and own culture, and so is probably the truth.
Historical studies, research and analyses are based on
documentation. The task of the scholars is to extract and concentrate information from ancient documents and manuscripts - anywhere they have the intellectual and linguistic capasity at disposal. There are not many scholars as are able to cover foreign cultures on the conditions of the same cultures, therefor the task of comparative studies seems rather difficult.
Many of the great cultures of our World have had their heydays some thousands years before the western, and many of those high developed cultures from Middle East, Asia and Africa are still jealously guarding their secrets and heritage in safely closed governmental archives, in former imperial libraries or hidden in temples and religious centres - and none of these are specially accessible for western scholars.
Conclusion: We in the west doesn't know much of development of foreign worlds and their historical heritage.
In the western hemisphere we operate more types of characters:
Numbers written with Arabic Numerals (coming from India) consist of the signs 0 1 2 3 4 5 6 7 8 9. Numbers have the same value on different languages, even if they are pronounced with different sounds. Therefor numbers doesn't give so many cultural translation problems; they are inmediately understood, at least if the numbering system is known. But other signs too can represent a fixed value. The greek letter π for example, in the most cultures will be understood as the decimal value 3.1415
Attention: If the numbering system isn't known, then a notation as 101112 for example could be a decimal number or a date as could be yymmdd, mmddyy or ddmmyy.
Letters, as expressed by the Latin Letters and the derived alphabet of lowercases are connected to a sound, and these sounds can be combined by their secuence to form a word in a sentence in a local language. But here the sound of a letter has to be defined by a linguistical agreement, and is therefor never the same passing to next language or dialect.
Letters change sound if used in another language; but the advantage is, that we only need a few - (25-40) - different letters to express any word in any language.
Other signs exist in western hemisphere alongside letters and numbers. We have drawn signs as metaphors, representing meanings more than sounds, indicating ideas, assigning instructions etc. being symbols for words and phrases, just as the writings in oldtime Mesopotamia and Egypt was expressed by hieroglyphs: pictures as represent letters/sounds/sylabs or objects/actions/ideas.
The disadvantage of that type of writing is that a written message in ordinary prose easily could need
thousands of signs
. Probably - I don't know for sure - the same is the case for Chinese, Korean and Japan writings - and perhaps other.
We are in the western cultures used to read and understand certain signs without greater problems - even meeting them in other linguistic areas. Examples of more international metafors could be: road and traffic signs, turistic pictograms, social emotions, logos and computer icons.
A warning Take care of your use of "international" signs, they are not always international outside their local area of birth. A story: Once in an Asian airport I watched an older gentleman with big grey beard as with a deep sigh of relief entered the door to a toilet. He was dressed in tunic and turban in acordance with his culture and exactly as the "international" door pictogram indicated: Soon after he came out very displeased.
The sad example of Quechua language
Quechua lost their quipu-writing and failed to adapt to their conquerors latin writing.
The Quechua language is a spoken language, they say, but they have had their "writing", as we now have lost and only find in few remaining but incomprehensible Quipus.
But any language is possible to write with latin letters, if we only define the basic sounds connected to the letters. Therefor the Quechua language as colonized by the latins is now written with latin letters based of Spanish sounds. Unfortunately each parson was concentrated to expres his Bible to his local parisioners, and therefor he took no responsability more than create a writing for their local vernacular. And each dialect got their writing, and as defeated people the Quechuas themself wasn't consulted. Therfor we now have around 20 dialectal right-writings for the nation of 10 million Quechua-speaking, and that make any witten intercommunication among Quechua-speaking people difficult - and that push every dream of any Quechua-written publication out of view, leaving them non-feasible because of short volumes. About Quechua language, the Incas speaking.
2): Things as the sailing people have to experiment and find out:
We can always discuss if the skipper is sailing his ship - or the ship is sailing with her skipper. In the case of Thor Heyerdahl, there is no doubt: that was the raft which sailed with him, and therefor he landed at the island where he did, and not where he wanted. Later on he learned to master sailing.
The situation now 70 years after the Kon-tiki navigation is, that nobody has sailed out and turned back again with any Pacific raft !
Few have tried, but the most has only driven off with the wind as a balloon fly and in best of the cases sailed with broad reach - whereupon they left their raft abroad.
In spite of the many rafts and mystical vessels who have left the shore in the wake of Thor Heyerdahl's Kontiki we have got no account for the use and utility of daggerboards at Balsa rafts. We have developed the theories - but still nothing is verified of their function.
That we of course would like to see done better - and clearly documented better.
Therefor we want demonstrated how to steer a raft with Guaras and without any rudder - and we want to see that the rafts really are able to sail out and come back again to same site.
For example a short trip: sail out, tack, turn around an island and come back again to same haven.
Account of some steps in the rediscovery of this strange Guara-system:
A first try to follow the wake of the old rafts and reach Mexico was done by the unfortunate Manteño expeditions as John Haslett has told in his book: "The Lost Raft". They did a good job. They steered by guaras and that worked satisfactorily, they say, but they lost all their four rafts of other reasons - mostly because of the ship-worm Teredo Navalis.
Tangaroa Was a Peruvian raft as inspired by Heyerdahl in 1965 sailed from Callao to Fakarava Island. Nothing is published, but we know that Tangaroa equipped with only 3 Guaras passed the dangerous Tuamotu Archipelago of French Polynesia by own means.
Tangaroa-2 was an expedition which 2006 sailed off followed by many expectations to results - perhaps due to the name Heyerdahl was involved - and because Thor Heyerdahl was deeply respected in Peru - especially for his work with the pyramids of Tucume in North-Peru.
The raft was equipped with only Guaras and no rudder. The cruise turned out to be one sad case more, as after 10 years still not has verified any of the Guara-theories, as so many have expected. The Tangaroa-2 expedition among other had the objective: "To demonstrate the versatility of the navigation system with Guaras". If they have a result, as they say they have, at least no book is available with accounts around the navigating and beating against the wind by Guaras = daggerboards. But we have this article from the internet of a foreign country.
Years later the same Norwegian group started out with their Guara steered 'Expedition Kontiki2' where they lost two rafts in the middle of South Pacific. We are still waiting for tecnical evidence from both expeditions.
A funny but crazy sidestep
In 2011 the raft An-Tiki, as was a highly modern craft, so modern that it was made by high density polyethylene water supply tubes, crossed the Atlantic.
The Steering from their description:
There were two types of steering. The first was twin rudders at the stern (as they broke), but also 4 traditional Guaras (daggerboards) at the corners of the raft and as supplement they furthermore mounted a long central steer-oar, what could be a good idea, because such could row the stern sideways and in that way correct the pointing course or go through a tack - if they at all tacked.
One more sad result: No evidence given around Guara sailing nor any of their steering systems.
Beach and de-beach
Within the advantages of balsa rafts is their low draught. But how to land those huge vessels on coast and haven is another theme around seamanship still non-explored. In the time of the Incas were no harbors and no motorized tugboats, but nevertheless the rafts were able to land on a beach by own power - go to shore, beach and de-beach again by sail, poles, oars, paddles or by warp (hauling by an anchor).
So they did, and they did it so competently that they later were used by the Spaniards as lighters to load and unload their ships.
We have no investigations nor experiments of how they did. To day we have no knowledge of how they landed their cargo - nor how they did a dry-out of the trunks, if they needed that. We simply don't know, how to handle these big block-boats for beaching and de-beaching by own crew - on an open coast with waves and perhaps breakers. That isn't known, because the balsa rafts disappeared hundred of years ago.
How to handle and hoist a sail
How to handle heavy sails without sheaves nor blocks in top of mast?
Of course we ponder over if the South Americans really were without sheaves and blocks. We simply puzzle what they had in top of mast with only little friction to turn around a halyard for hoisting a sail so huge as the chroniclers tell about. We have no idea of their rigging.
As pointed out, we know that the Incas not used wheels then (but now they do). Why, we understand very well when we have been on their steep mountain roads, impossible for any cart - but had they sheaves, blocks and tackles for their ropes, before the Spaniards taught them? How did they hoist their heavy sail without sheaves? That is still not known and we can't imagine. Perhaps a couple of hands more to haul the braided halyard through a wooden eye.
Test and investigation of such a point could simply be by a demonstration of practical tries.
Supply for long raids on sea
What provisions of food and drink is too today needed to bring with for a 2 month cruise. In some way we too like to understand in what a grade an original sailing raft was self supplying under, lets say 2 month fishing on the ocean.
From my boy-scout time I know for each crew to calculate 1 kilo of food and 3 liters of water a day, so were they really bringing fresh water and life stock to eat and drink for two months - or could they live of what they caught. Tupac Yupanki was more months on the sea with some thousands of men, and he needs to have had a solution of that logistic problem.
Such information and experience we would like to get from the active raft sailors - simply to be able to understand better, what they could then in the past culture. Whereas we are not really interested in some miles or some months more or less to some fantastic destinations. Those records should be given over to the 'Guiness book of records' for the beer-drinking people.
Sailors and shipwrights must know it. We have seen different technical solutions for Guara holders but of course we would like an evaluation from the sailors about the NEED for special holders for Guaras.
What did the ancestors? Did the Incas at all use holders for Guaras/daggerboards? or could they plunge them in between the balsa trunks without sophisticated guiding arrangement - just where they needed them.
Does anybody know what are they doing in Ecuador, where they still today employ balsa rafts?
Building raft on Wharf
Building on a slip-way or steel-frame will give us a smooth underneath - but the price could be a leveling with a chainsaw
Theoretically there is a difference in result between the methods of building.
A): Building on slip-way, laying up the trunks on an even plane give a smooth underside, but the price could be cuts in trunks to make a junction with next layer of crossbeams -
B): Building floating in water or laying the trunks on an adjustable support - can give a smooth topside together with the opportunity to get a profiled underneath as for example a fat trunk for keel - and too a chance to make the junctions with the overlaying crossbeams without serious cuts nor wounds in the surface.
Cuts in the buoyancy-trunks open up wounds for easy penetration of water = quicker water-logging, but we have neither any investigation of the working life before water logging of the natural balsa trunks - nor nothing about how to dry them out in between their crossings. No investigation of a possible protection of trunks against water-logging (tar, oil, grease) - or even worse: an attack of the ship worm Teredo Navalis.
The question arise if the Inca-rafts were build on the beach - or in the water?
And here we too would like some response from experienced raft-builders.
There have to be something to learn in Ecuador, where they still are employing Balsa rafts for minor purpose.
3): Things as we hope the scholars can find out by archaeological finds, dig-ups or by comparing science.
Old anchors don't disappear so easy, they ware probably of stones, 'as our millstones' as the Spaniards wrote, so we expect one day to some will show up.
The archeological part is still missing, as the historical part - furthermore very few archeologists and historians know anything about the art to sail a vessel with sail.
The sailing societies created their civilization and lore on base of local material and common craft. Therefor it is important to define which materials was present and used in this maritime society - historical recognized or at least as accepted - but too which work-technologies was at disposition then.
Archaeological finds we don't expect much. Wood is very perishable, but can survive in protected areas, as the models of Guara have done in the graves.
Here we have more expectations to a comparative archaeological science, where we can study and compare same technology in different relations and finds. For example choice, handling and use of plant-fibers for threads, yarn, rope and textiles. Tools for carpentry and wood laboring in those old cultures - perhaps followed up by practical and experimental tests and trials.
To get this understanding, we of course have to study ropes on still maintained suspension bridges and textile technology, weaving and looms from other areas.
Woodwright tools and working with tools - but which tools
We don't know much about their working tools and their technology (how to use these tools) with materials of then - we want to see trees cut down, wood worked, sails woven and sewn with technology of that time.
Of course we to day will cut a balsa trees with a chain saw, as every modern man will do. But we know that saw cut trunks they didn't employ - they hadn't any saw for their prehistoric vessels. Probably the old Incas hewed threes with an axe of some type, but which one we don't know, because we have no knowledge if the Incas for that type of task had other tools than some of hardwood or stone (as their weapons ware of stones) - but nothing is proved.
There must be something to learn from those Museums as show working exhibitions from that time. They at least have had some material in own hands, as not only are documents.
Shipwright technology in the level of what they dominated then.
That is a technical area as isn't very well studied. All the museums we have seen demonstrating living conditions in the past, they use ropewalks and weave technology coming up centuries later. Anacronism isn't honest.
We would like to see something repeated about their original rigging using braided or twined ropes in long length - and made without use of any ropewalk.
Ropes No evidence of the ropes, fibers for ropes and use of ropes employed by the balsa rafts: Twisted, plaited or what?? And done how? By rope walks or in hands? We have an old report from Pascual de Andagoya: that "the inhabitants have a manufactory where they make cordage of a sort of Henequen" - but what is that telling us today?
But as said, we know something around ropes used for Inca bridges, and there a profesional study perhaps could bring more facts.
Sails - and cloth for sails?
Sketches of balsas rafts we have several. The Spaniards made more descriptions and drawings. In general they are shown with a single square or trapezoid sail, and never topsail nor staysail, but sometimes however with a little foresail, where the tiny foremast perhaps was more used to fasten a bowline for the main square-sail. But even with these old sketches, we are missing details as for example how their sails were manufactured - or the mounting and fitting. Could they produce canvas in continuos /endless length or did they produce sheets sewn together?
An A-mast seems a common equipment for rafts. We don't know of which wood, probably a local grown tree. An A-mast means a mast without need for shrouds. By the European vessels it is the stays and shrouds more than the mast as take the wind forces.
But even if the most common mast tree in Norway is Fir and Pine, we have no reason to assume that the Incas have imported any Pinewood - neither from Oregon. And as told: Eucalyptus, as today is very loved in South America, was still kept within Australia, until it came as an insect-resistant wood for ties to the railways.
An interesting remark around reed-rafts from Lake Titicaca:
Roskilde Viking Ship Museum:
A replica of a Titicaca totora boat - made by Paulino Esteban, the RA2 reed raft builder of Thor Heyerdahl
Rigging of small totora reed raft:
The rigging is in three places marked red: ∇9, tied by slipper hitch. Releasing this, the double mast with sail can quickly be laid down either against stem or stern.
Some ideas arise studying the rigging of a classic totora-reed-raft as still is produced on lake Titicaca. Looking on the small boats there, the question arises, if the south americans on the Balsa-rafts hoisted their sail ON the mast - or they as at Titicaca raise their A-mast WITH sail set.
An A-mast is rather easy to raise - because it doesn't try to tilt.
We have still not seen any ocean going reed-raft replica use other than sail of canvas. Still none with totora-reed sail.
How good or how bad this South American totora reed-sail work, we have no sailing experience. But with its long "battens" of totora-reed we would classify it as a version of junk-sail.
The photo indicate a sailing with beam reach.
Note that the air pressure at Lake Titicaca - 4000 meter over ocean level - is around 60%
The technology applied for the ropemaking is mentioned on page #3
4): Lost themes without expectation for recover:
Navigation over an ocean
But how did the inca-seamen find their way over the enormous ocean to its distant islands - sometimes filled with dense fog along the Humbolt Current, that is difficult to say - but they did. They did it so reliable and competent, that they were able to sail out with their later sovereign ruler - Inca Tupac Yupanqui and his army - and they could return him to his future realm.
How the Inca Tupac Yupanqui could steep down from his mountains and trust on a navigation with a full flotilla to some very distant islands in the Pacific, that is too a very interesting theme to ponder over. In some way he must have got experienced sailors as captains and pilots.
But who was his navigators? - and from where did they come? We can only guess. One guess could be an interchange with the sailing communities from some Polynesian islands - but such a theory seems nearly impossible to get verified.
In this relation we would have liked to know by which means of technology this past cultures made navigation, made crossings of the wide ocean, hit their desired destination among the scattered islands and were able to find and find again the same islands.
This seems as a MAGIC sense for non-instrumental ocean-navigation.
The time when such was possible has passed. Now we only can admit, that we have lost any ability to activate such mystical power - and too lost the lore connected. That was changed with the upcoming nautical instruments in such a grade, that we today firmly can declare, that we don't expect anybody being able to navigate without instruments as compass and GPS - maximum we kan keep a course relative to the actual wind, hoping that the wind will remain steady.
We must accept it as lost - and let the question stay as an unresolved riddle : "how did they?".
A ruddersteered boat without hand on tiller will tumble around, that we know of bitter experience - but a Guara-steered raft not!
All the Guara-raft work as a wind-vane - and with the same guaras plunged down, the raft keep a steady pointing sailing over the ocean - in relation to wind - and that is at least a help for navigation.
Furthermore the logistical part. How did the Incas organize a fleet, sailing out with a host of twenty thousand men - what means a flotilla of 1000 balsa rafts - or perhaps less, if the numbers have grown each time the story was told.
How they organized those far away sailings as that of Inca Tupac Yupanki: one year away from home, that we only will be able to understand when we understand their organizations. But that information we only have very scarce from their conquerors, and axactly the conquerors, we can't trust as an objective source. The Incas was technological subdued - not organizational, and even if Maria Rostrorowsky had done a huge investigation job, the descriptions we have, are all from the "winners" of the war, and not a single word from the Incas themselves.
The Teredo Navalis menace
And all our post-Heyerdahl raft sailings have taught us that we have to keep attention to how they could keep their rafts floating in sufficient months to make their voyage untouched by Teredo Navalis, the shipworm.
The Teredo Navalis is a pesky and greedy animal as have eaten up several vessels. Twelve of the twenty rafts as after WW2 sailed out on the Pacific Ocean were lost - and at least 6, but perhaps more, was sunken by Teredo Navalis.
"On this occasion they took a Peruvian bark, strangely rigged, having 6 stout natives on board, who have been out fishing for two month and had a cargo of excellent dried fish, which was distributed through the fleet."
2 months at sea means, that the natives had been able to dominate the Teredo Navalis danger. The raid of Tupac Yupanki 550 years ago was a one year voyage, and no sovereign will do such a seavoyage, if there were more than a normal danger.
What we really want is to clear up what the South Americans did - or could have done against this evil infestation. We expect that a process of drying out the trunks on hot and dry beaches and an treatment with Pitt asphalt, could be a part of this, as the raft sailor and writer John Haslett indicate. John Haslett is our probably most experienced Teredo Navalis fighter. Ref: his book: The lost raft - ISBN 9780692545263.
We really don't trust of all the strage legends that trunks has to be of female gender and cut down by native farmers in full moonlight. Such tall stories exist only because we don't know better.
5): Teredo Navalis - the Ship-worm danger
We have no reason to think that Ship-worm attack is sometning new
Simple attack by shipworm
The greatest menace against ocean sailing rafts is the Ship-Worm - Teredo Navalis. That is a clam as has sunken thousands of ships.
the coin looks like an US-one cent as hold a diameter of 19 mm
petrified infested wood
In post Heyerdahl time around 20 rafts have tried to pass the Pacific Ocean. Only 8 have done it, and 12 were shipwrecked. Of these the half went down due to the Ship Worm Teredo Navalis as simply have eaten up the trunks from inside under the sailing, whereupon the trunks had lost their buoyancy - and sunken ! An unknown number of those rafts, as had arrived to their destination or where they ended were so hard attacked, that they wouldn't have been able to take the return trip. None of the 20 experimental rafts has returned to their port of departure.
Of cause we are aware, that the softer the wood is (e.g. balsa, pine rather than oak and Guayacan), the quicker the advance of Teredo Navalis will go on. That means that they, the South-Americans, even before arrival of the Europeans must have been able to handle, protect and sail their rafts under more safe conditions. Better seaman-ship, better Teredo Navalis protection etc and that is exactly there, on the unknown and uncertain points, we need to concentrate our archaeological investigations and experiments. What did the Incas?
Ship Worm attack is nothing new. In historical time the chroniclers tell, that men as Christopher Colombus and Francis Drake had to combat hard against this plague.
On his fourth voyage to his India year 1502 Columbus came to a disastrous end, when all his ships sank due to damage from Ship Worms, and he was forced by these small clams to land on Jamaica, where he and his crews were marooned for a year before being rescued.
From a letter describing his voyage, the ships were: "… rotten, worm-eaten … more riddled with holes than a honeycomb. With three pumps, pots and kettles, and with all hands working, they could not keep down the water which came into the ship, and there was no other remedy for the havoc which the worm had wrought… from Columbus letter: "my ship was sinking under me…"
And Francis Drake too had to land on the Californian coast to do a fundamental repair on his ship, the Golden Hind, which had been damaged by shipworms.
Of cause there is doubt how widespread in the Seven Seas this clam was in Inca time. Had it gone abroad together with the explorers 500 years ago - or was it present before. To support for the last theory, we have found fossil wood in Canada showing the bore holes of Teredo or a similar species from the Cretaceous Period, about 65 million years ago.
The Ship Worm Teredo Navalis is a wood-eating salt water living mollusc as doesn't like fresh water. That is a clam - growing to 30 cm and thick like a finger, and by its voracity and propagation this ship-worm together with its near family is able to sink a raft in few months, eating it from inside and out.
Despite the common name, Ship Worm this is NOT a worm, but a worm-shaped clam. Anatomic head of this clam is equipped with hard points to grind the wood - followed by a body bringing backwards the waste. That is the two valves of its shell, the nature has modified from protective devices into two small, but extremely effective grinding tool, that are used to bore into any piece of wood encountered in the ocean.
It work just like a TBM = a Tunnel Boring Machine as we today use to penetrate our underground making tunnels for trains or aqueducts: Cutting and milling the material with its jaws in front end and expelling the tailing backwards.
The clam starts out as a small juvenile larva, that settles and start its destruction on a wood surface. As the hole gets deeper, the animal's body elongates to maintain a connection to the surface, and the burrow is buttressed with a shell-like chalky lining - all like we prolonge and line a running TBM.
The Ship Worm is simply hollowing out the wooden planks or trunks from inside - there is not much to see from outside surface.
Teredo fresh and alive ready to be taken out
note the drilling jaws and the 'tailing' against rear
A man-made TBM is designed in same way: cutting head + lining and tailing exhaust
The Archaeological Perspective
As named before, at least 6 of 20 rafts was sunken by Teredo Navalis - but perhaps more, because we miss exact information - and more rafts at arrival to their destination were attacked by the animal in such a grade, that the raft wouldn't have been able to return.
The earlier archaeological Mantenna expeditions, were hard beleaguered by Ship-worms, as sunk three of their four rafts, and they indicate therefor some treatments within the Inca options. An interesting account of this is written in the book of Cameron Smith and John Haslett: "The lost raft"
or found on the web: "Construction and sailing Characteristics of a pre-columbian raft replica"
In the light of this fact, it is difficult to believe that Inca Tupac Yupanki would have sailed out with a great host on a year-long voyage, if he didn't have had an effective protection against Teredo Navalis, as can sink a raft in around 100 days
We don't know if the Incas have had the same problem, but as stated, we have nothing of written information from that time. Furthermore there exist that theory, that Teredo Navalis came to South America together with the Spanish caravels.
Even if it really seems difficult to believe, that there were no Teredo Navalis in all the Pacific Ocean before Columbus, and they therefor didn't need at all to impregnate, so the fact is, that the Balsa rafts kept on sailing along the coast with all the menace from Teredo Navalis - until around 1920, so logically they must have had something - now forgotten - to protect their rafts.
In all cases it seems really difficult to understand how the Incas could make ocean sailing if they couldn't combat the ShipWorm. I cant imagine how they could sail out on a year long voyage under their later sovereign Inca Tupac Yupanqui and with his army, if the risk was to lose 25 % or more of their rafts during a voyage of first few months. That sound for me more as a hostile plan to provoke a shipwreck.
Conclusion: Any wooden raft has to be PROTECTED against Teredo Navalis
Today we probably would kill infesting animals with chemical materials. Nevertheless the Archaeological task is to find at least one way of which the old South Americans could have protected their rafts under their month-long sailings.
Some possible solutions
Impregnation with Tar, eventually Tar mixed with linseed oil, we use in Europa for conservation against rot of wood and ropes of plant-fibre and but too to protect against infestation the wood eating ship-worms - or we sheathe the hull so the larva can't enter and start attack.
In Arabia - we are told - they treat their crafts with a mix of Goat Lard and lime chalk. That paste protect against infestation by Ship Worm but not against fouling. On the other hand, that shell of protection is easy to knock off together with the seaweed - and then daub on a new layer.
The principle of attack: land as a tiny LARVA - get hold - and enter
- and then hollow out the wood
In Puerto Pizarro, in North of Peru near the frontier to Ecuador, several years ago I met a man, who sailed tourists in his home-build dinghy. He treated his wooden dinghy by painting it over each year with a mix of tar, cement and Baygon = a common insecticide from the local shop.
That man had resolved his ship-worm problem in his own way, but if we want to make serious archaeological experiments in Inca rafts we have to find out, what the Incas did. In other words: if we depend of modern chemicals, we will have difficulties to defend our research as serious archaeological experiment - under such anachronistic conditions.
We have never heard of wood-tar extraction in pre-columbian South America, but had the people around Manta other means? If we can't cover the trunks, what about impregnation with venom or poisons, as could be used preventive and work as protection. Perhaps an animal grease of any type could have been used, as they did in Arabia.
We don't know much, but one answer could be, as John Haslett point out in the end of his book 'The Lost Raft', that natural asphalt as is found as tar pits, asphalt pit or rock asphalt around in the Andes Mountains. So we can state, that a protective coating of the balsa trunks was possible - but we have no evidence.
With reference to History of Trinidad:
The Pitch Lake has fascinated explorers and scientists as well as attracting tourists on the island of Trinidad. The American Indians knew about and showed it 1595 to the British Sir Raleigh. That was short time after the Spainiards had met the Balsa raft, and Sir Raleigh himself found immediate use for the asphalt to caulk his ship at Trinidad. He referred to the pitch as "most excellent... It melted not with the sun as the pitch of Norway".
I personally have met and used pitch tar in the high Andes in a altitude of around 4000 meters.
One thing is to avoid infestation - a more serious task is to cure an attacked raft and kill the ship worms inside the trunks, and that is theoretically only possible by drying out the trunks - what is very difficult to do under the navigation.
Another way to combat and kill Teredo
Ship-Worm is abivalve and like both cockles, mussels and oysters it is edible and is eaten in countries as Thailand and Indonesia as a delicacy on level of oyster. The attractiveness of such a meal as always depends more of the cook and your own preconceived opinion - and not so much of the raw material.
Try to google: "Tamilok".
Delicious or Not - that depends most of your own culture
In some way we can accept the paper of this clam in the great housekeeping of Mother Nature. This clam Teredo Navalis and all its family work as ‘garbage men' of Gaia - cleaning up.