Print Friendly
[ img - print2.png ]
< The inca's balsa log raft
- Seamanship on rafts
- A desktop exercise
- The Pharaoh's reed boat
- Catamarans with trimboards
[ img - inca-sol.png ]Quechua
[ img - tumi2.gif ]Hotel in Lima
[ img - egypt-image.png ]Similar steering ?
[ img - raftlogo.gif ]
[ img - incaruna.gif ]

Addendum to
Inca's sail powered Balsa Log Raft

The loss of two Square-off rafts

When things turn wrong, what is the reason ?

- and what can we learn from that ?

two rafts more lost on sea
The story - short.

That is not every day we hear about a square-off raft driven by square sail, but the Norwegians designed and builded two - and they paid a hard price for that experience.

They came rushing down to our coast, builded two new models of Kon-tiki rafts, sailed out on the wide and pacific Ocean without previous test of their new design, and discovered on their way, that they with no combination of sail and Guaras were able to beat against the wind.
Nevertheless they continued their sailing and drifted with the trade wind, as brought them out of route. After some months drifting around in the South Pacific, they found themselves 1200 kilometers south of Easter Island and without possibilities to sail back to South America, therefore decided to abandon their rafts in open sea and call for pick-up - and with that they gave up every chance to recover their costs and regain investment.

- 12 of the 20 wooden rafts sailing out on the Pacific Ocean, never reached where they should
Why tell this sad story?

Nobody think that this was a happy experience for the crew - although unforgettable. Drifting far out of planned route, turning south to catch the cold roaring forties, where the western wind destroyed their rafts and cold water washed through both crew and equipment. Such months on sea are not fun, but we have to admit, that hard and bad experience too is experience, as could be fruitful next time, as they - or sombody else - want to try again.
This is a grim account, but we need to tell the story to extract learning for common use.

Allegation around Guara-steered rafts:
If a raft can't beat to wind it is NOT a Guara-problem
- the problem is either the sail or missing seamanship (knowledge) -

What was the hazards for the Norwegians ?

They had made changes to the classic inca-raft bodies - on the hulls, but they had carefully tested their theories by tank-tests.
They had mounted a typical Norwegian mono-masted square sail - and that rig is the most Norwegian rigging, as is possible to imagine. They have used that rigging the last 1000 years - and they master it to excellence.
That should neither be their crews. The rafts had all experienced captains and around the half of their crew were full-bodied sailors trained on square sails - the other half less.
They came with the experience from a successfull raft-raid - Tangaroa-2 - as 10 years earlier drifted west over the Pacific; so they knew that ocean - and they knew the use of Guaras.
They knew from the old Spanish chroniclers, that the chosen months would be the worst to sail to Easter Island. Impossible in Inca-time.
Too they knew, that the year was expected to be a bad 'El Niño' year, as affect the global climate with atypical and unpredictable weather
- and they felt themselves strong and prepared for such conditions at sea - and they were! No doubt around that.
the Shipwreck

The Norwegian impulse to this raft manual

Their old raft Tangaroa-2 they had sailed perfectly 10 years earlier, and even if their actual difficulties seems to arrive together vith the introduction of the square-off bow, then it was this incomprehensible dual shipwreck, as caused the decision to collect the experience and write a 'sailors handbook' for next generetion of raft skippers.
And with this manual we hope to see well carried out raft raids in the future.

As told, they build and sailed directly off without test nor trial of their new hull shape, and a month into their sailing, before they reached Easter Island we received the message

Cite: "We can't sail closer than 100 degrees from wind, 90 degrees is not possible, no matter how we position Guaras and sail"

100 degrees to wind is in no way against the wind, but that message didn't give reason to worry, because the expedition would call Easter Island, and could mend their problems there. But that was the last words we got directly from Kontiki2 expedition.
No explication, and we have still not received any oficial report, but on the other hand we neither expect it.

As we see the case now long time after the unfortunate raid it was a mix of more small errors - as together gave a big problem:
1): The square-off bow invited the raft to sail along a diagonal - and therefore they crabed ahead  
2): A baggy sail was adjusted for sailing along centerline - and they sailed along a diagonal  
3): Too many Guaras plunged down may make a Guara-raft immun against steering - and that seems as what happend  

A solution of any of these smaller problems could have eliminated the main tacking problem and brought them back to South America.

The Message from the raft "Rapa Nui" of the Kontiki2-expedition together with the later air-photo picked up from their own web-site: gave us the kick to try to find out, what could have happend. Gave the impulse to this research: to find out the generel theories around Guara stering, raft sailing, hull shapes and sail, as all is written in details on the earlier web-sited. In short: a manual for raft skippers.

[ img - neptun-logo.gif ]
Their fault was NOT to make an erroneous design - that they could have mended
Their bad result was basicly due to their rash and reckless start
- and the irresponsible was, that they sailed out without previous test of their new creation -

The lesson seen with hindsight - years after the happening

The understanding of what may be the reason for the Kontiki2 calamity came late. Came years after together with the appearance of the old Tangaroa-2 photo - showing an overcrowded underneath, as not permitted CLR to be moved sufficiently backwards.  
the preparations before start

Pre-analysis to choose square-off hull shape

The first suspected for provoking their bad sail result was the new hull of their rafts.
The testimonies from early explorers all have told us, that the South American rafts without visible difficulty could beat against the wind steered by their Guara system.
The common shape was reported as a long trunk in the middle and some smaller along the sides - as the shape of an outstretched hand.

That the norsemen changed. The rafters wanted to build "a fast sailing balsa raft".

Transcript from 2015-09-03:
"Building and testing raft models - How should one best build a balsa raft? Pointy front? Shaped logs? Does it make a difference?
Crew member Ola Borgfjord has built several models along with his father, Einar Borgfjord.
The results indicated, that a curved front and tapered logs in the back will be a good choice for the rafts."

we don't know -
if the tank-test was made without or with full set of waterbrakes = Guaras
[ img - tank_test-rafts-sept.2015.jpg ]
Tank test at Technical University of Norway
pure traction straight forward and no sidewards forces tested

The group carried therefor out comparative hydraulic tests in a water tank, measuring water resistance in relation to sail-speed for different raft models. Subsequent both rafts were remodeled and constructed in accordance with the scientific result, as the tank test had indicated. They amputated the prow from the classic balsa raft and build a pair of tween rafts for their raid with square-off bow: 'stub-nosed and sloped'. They maybe could reach up to the double speed with this new hull shape, they expected.

The tank test

The performed tank-tests demonstrated, that the chosen rectangular hull in flat calm waters could be pushed or towed ahead with a low forward hydraulic resistance -
What they registered on their rolling test-bridge was probably only hydraulic resistance by different speeds, because that was what they had asked for.
We don't know, but are nearly sure, that the test rig of the tank didn't register nothing about things as 'influence of wind abeam', 'directional stability' etc. nor any torque from a one-sided bow wave, as arise for example, when sailing with the wind abeam, what on the raid showed up as crucial for the raft.
[img - Prow-Kontiki2.jpg ]
The prow of a kontiki2 raft the day of launch

The test result means, that to obtain this LOW FORWARD RESISTANCE as measured, the raft has to sail clean ahead as centerline is pointing - without any grade of leeway - but that is a situation as only will happen, when sailing directly downwind.

Anyway, the test was fair enough, because toogether with the long straight side trunks as will work as keel, the raft-shape met the conditions for being powered by sail:

"LOW forward hydraulic resistance + in combination with a HIGH lateral ditto"
- and what we later saw on the ocean -

What we saw on the Photo

Photo of the Kontiki2 raft Tupac Yupanki south west of Easter Island - taken 25.Febr.2016 by a toy-drone

A Guara-raft as you can point in whatever direction you want - says the rule

- therefore that can't be a Guara problem, and the crew will find out, was our reaction
- if something with their bow, they at least have time to mend under their comming call at Easter Island.

But that they didn't
They sailed out again to lose their rafts.


The raft shown on their air-photo make an extreme broadside motion. She holds a rather rectangular shape, with a l/w ratio around 3:1 and a transom bow - she seems to use her starboard (lee) corner as prow. The position of the Norwegian flag indicate apparent wind directly into port side = beam reach. The lifted front-end of port trunk together with the dipped starboard trunk-head indicate a good wind. The wake drawn from port side bow and too after the raft both indicate a leeway - a deviation from pointed course (centerline) of around 20 degrees - and that is much.

The yard is brased 60° to centerline = 80° to sailed course. The sail seems adjusted fair - but not good - not even if sailing along the centerline with wind abeam.
In this case the raft is NOT sailing along any CENTERLINE, she is sailing along a diagonal

[ img - RaftOnOcean-60.jpg ]
the sail is not adjusted good - however fair, if they was sailing along the center line, as they do where this Nordland rigging comes from
- but that they didn't
the semicircle of CE = Center of Effort for a lonely square sail
[ img - squ-raft-60.png ]
Yard 60° to sideline, but sailing along diagonal (+20°)
first problem: the changed bow

The tricky transom bow

[ img - Compass_Rose.png ]
a Guara-raft can point all the compass around

A flat-bottom log raft with wind abeam hold a preference to sail with lee front-corner as prow; and without counteraction taken she will sail on crabing ahead. Nothing wrong with that, because at least we are sailing with the wind. The only thing to complain is, that she doesn't get the LOW forward hydraulic resistance, as we measured by a tank-test, simply because she isn't sailing straight forward - but sailing diagonal.

The counteraction concerning the hull is to balance the sidesliding of aft against that of for.
With that done you will be able to sail as normal along a centerline. The means are: brake the aft leeway by plunging more Guaras down aft (and dont forget to lift up the foremost) - or by dip a steer-paddle on aft lee-side as sidewarts waterbrake.
By correcting you will sail-on along the centerline of the craft and obtain the lowest forward hydraulic resistance as expected - but of course you too can sail-on along the diagonal. That is your choice.

The common rules for pointing of a Guara raft is demonstrated earlier:

If steered by rudder or steer-oar the same raft wil do the same. A square-off raft will go diagonal and behave just like every vessel with too little rudder or without skeg aft: sidesliding of aft.

The nature of bows, if no counteraction is done:

A main difference between a pointed and a square-off raft is that the later need some more Guaras plunged down aft to compensate the unidirectional deviation of bow-wave
- or alternatively to position the mast more ahead (as the Humber Keel) - or hoist a foresail.

And in a technical language that means: either draw backwards the CLR - or move ahead the CE - to keep the CLR-CE linie = 'direction of wind' on the same line across the vessel.

A pointed raft will sail-on, as pointing along centerline
+ with a few degrees of leeway
[ img - raft+fish1.png ]
The pointed bow will split the bow-flow to both sides
In all the cases:
- with wind abeam skipper still has to forsee certain leeway
A square-off raft will use the corner to divide the in-streeming water and sail-on along the diagonal + added the same few degrees of leeway
[ img - raft+fish2.png ]
The one-sided bow-wave will go in balance with the water press on the lee side
With sketches of water streaming against the bows of two comparable flat-bottom rafts, we here try to explain, that a raft with pointed bow, immediately will try to correct a deviation to the pointed course by applying more water-press on lee bow and side
- whereas a square-off bow first will find the balance, when the raft has passed the diagonal, where the press from streaming water on lee side is in balance with the press of bowwave on the square-off bow.  

Course and pointing is two different things. You only have to take a look at the eel-drifter, to accept that assertion,  
On the eel-drifter the course is drifting with the wind across the the centerline of the boat - whereas the pointing is along her "nose" across the wind. Just as a boat 'heaved-to'.

You can control the pointing of your raft all the Compass around with your Guaras alone,
as the Center of Wind will blow to lee of the Center of Water Resistance

- if the sail is adjusted for the now pointed course, you are sailing -

even if we sail diagonal, we are NOT accustomed to mount rigging along a diagonal

Struggling with square sail rigging on square-off raft

[ img - shipshape+.png ]

"If the sail is adjusted for that course" - - - exclaim the raft-rule - - - "så vil du sejle"

The rule for adjusting af sail
TRUE course and APPARENT wind are the parameters for sail adjustments
TRUE course is the direction of your wake
APPERENT wind is the direction of your flag or vind-vane

The square sail.

A lonely square sail has not many options to move around with the wind-center. With push or lift in sail the CE-center is principally the center of the canvas, and the canvas transfer the wind-forces to the boat by 3 fix-points: the tack, the sheet and the parrel.
The parrel does, that we can swing the sail around the mast, and the wind centre will therefor allways stay somewhere on a half-circle. And with that knowledge the rest of pointing must be done by our Guaras. To thrust the raft ahead, the pointing of craft and the adjustment of sail has to correspond - and that is the art of skipper to make that.

And here it is where the Norwegian raft sailing went wrong 2015:
Adjustment of sail
the TRUE COURSE is the steered course + and the leeway together

the WAKE or a floating log-line would indicate the TRUE COURSE

[ img - sail+sea+wind2.gif ]
APPARENT WIND is the geographical wind + and headway together

the FLAG or a wind-vane in top of mast indicate the APPARENT WIND

If sailing ahead, the MAIN-RULE for a square sail is that it (+yard) has to divide the angel between the apparent wind and the sailed true course.
Even if a raft is sailing diagonal, the square sail (and nearly all sails) has to divide the same angel between apparent wind as indicated by the windvane in top of mast - and the true = sailed course as is indicated by the wake of vessel. (And that has nothing to do with where the "nose" of the vesel eventually is pointing)

A conceptual error?
They probably didn't realize that it was a sailing along a diagonal they performed, and therefor they didn't adjust their sail acording to the sketch above.
Their rigging seems adjusted for sailing along a centerline - adjusted in same way as all their square rigged boats has been the last thousands of years in North.

Link to: Theoretical desktop exercise around adjustment of sail - playing with CE and CLR.

The most timber log rafts are born with transom bow

The three counteractions as the Kontiki2 skippers could have done.

Counteraction #1
[ img - pointing2.png ]
more Guaras aft
Counteraction #2
[ img - pointing3.png ]
adjust the sail for diagonal
Counteraction #3
[ img - pointing1.png ]
cut a pointed bow

the BASIC rule:
Any Guara-raft you can point as you want
and if your sail is adjusted for that pointing - you will sail

Notes about Counteraction options

Counteraction #1): They could have eliminated their wry diagonal pointing by moving backwards their Guaras.
A Guara-steered raft you can point where you want, and therefore too along a centerline, as explained:
The pointing of a Guara-raft depend only of the hold in water CLR = watercenter against the CE = windcentret (centre of windpress on sail). The helmsman should therefor plunge down a surplus of guaras aft, as can move backward the CLR, and that may too mean: lift up all fore Guaras.
Missing foresight:
Sadly - but we have never heard about any raft skipper testing and trimming his craft before sailing out on the huge ocean
With other words: set down AFT Guaras to balance sidedrift of AFT-end against that of fore-end.

When their raft is pointing as they want, and they sail ahead, then they may optimize their sail and Guaras acording to sail speed.

Counteraction #2): They could choose to sail on "crabbing" along the diagonal - what they really did.
If they really couldn't find out to adjust their pointing, skipper of course could accept the state of the raft and chosen to sail along the diagonal. As the rule says "if the sail is adjusted for that course, he will sail".
The sailing depend only of his sail and rig, and in the diagonal case, he has to adjust all the rigging in relation to diagonal, and not the centerline: turn the yard, move fastning of both tack and sheet. And this seems as the main-omission for both Kontiki2 rafts, as is rendered probable by our desktop exercise:
To turn the rigging to diagonal sailing, probably means too a moving of the forestay to get space.

Don't forget that the tank-test was based on a straight forward sailing to obtain the promised 'LOW forward hydraulic resistance' - therefore the tank-test could justify the first and the third solution.

Counteraction #3): The calamities seems came together with the square-off bow
They could have eliminated the problem by sharpening their bow
Simply take a saw and cut the wooden trunks in pointed shape or mount a "snow-plough" as Thor Heyerdahl used, as can divide the incomming bow-wave in two equal streams.

Attention in all the 3 cases:   Plunging too many Guaras down to "create keel" may obstruct the steering:
the ability to handle a sail-craft
A real seaman is expected to navigate any vessel, as can float on the sea
[ img - seamanship.png ]

The skill, techniques, or practice of handling a ship, a boat or any sailing vessel at sea

That is not the primary purpose for a sail manual to judge crew and seamanship. Our task is to analyze what happened, point out solutions, explain and in that way teach next skipper how to combat such problems. We have only to say, that their month long sailing on the South Pacific Ocean they had more choices for counteraction - but they chosed to do nothing - and lost their rafts.

That was perhaps an ill-considered idea and a silly fault to change a well-proved hull shape, but the fatal and decisive arised in the moment they in their eager to start their Heyerdahl-adventure, against all their Norwegian traditions pushed aside every final test and trim of their new ship-construction before sailing out on a monthlong raid.
The well established "prøveseglingsprosdyre" = 'procedure of test sailing' described by Jon Godal, their own compatriot, they left out.

The antique Greek rule is still valid for seamen:
If provoking the Gods, then they make their Nemesis follow your Hubris

They escaped the test sailing and got troubles, but as named before: the seamen = skipper + crew still had 3 options to fulfil the intentions with their raid.

Seamanship. The great historical question, as arise after the hard experience with this raid is around the need for experienced seamen.
If Tupac Yupanki as native governor came down from the mountains and really sailed out on the sea with 2.000 (or perhaps it was 20.000) men and soldiers on lets say 100 rafts, he at least should have one experienced sailor on board each raft. From where could he then get so many experienced skippers ? ??

What else could they have done to escape the sad ending ?

Nothing has been expressed from the teams of what they have done - or not done. Silence!

But we know from their departure, that the distribuition of Guara-slots on both Kontiki2 rafts seems to give sufficient options to make any ponting all the compass around.
If skipper want some other pointing than his actual, he only has to adjust his Guaras - and then his sail.
- to change a diagonal-sailing to centerline-sailing he probably has to plunge all 4 AFT Guaras down - and the rest UP
[ img - RahitiTane-slots.jpg ]
Distribution of Guara slots on
Rahiti Tane and Tupac Yupanki
[ img - TupacYupanki-slots.jpg ]

Overkill warning:
One thing is Guara-holders, but don't fill up your raft-bottom with Guaras!

Over-filled Guara system = lost steer system

"We can't sail closer than 100 degrees from wind, 90 degrees is not possible, no matter how we position Guaras and sail" - was the alarming cry from the expedition on their way to Easter Island

They called later at Easter Island, and stayed there for a time, and we thought they would use the stay there to mend the errors: cut the trunks in a prow or something like - but no - they sailed out on the ocean and lost their rafts.

Around two years after the Kontiki2 raid this photo appeared as could explain what may have happend.  

10 Guaras or more underneath
- no comments known from Tangaroa2 of 2006 -

- that photo indicate, that Tangaroa2 never needed to beat against the wind?

[ img - Tangaroa2-guaras.jpg ]
The photo show the underneath of the Tangaroa2 - a raft sailed by the same group of Kontiki2 navigators 10 years earlier.

EUREKA (as the Greek scientific Archimedes exclaimed)

If realy so the underneath, as the photo show - then we have found the reason for missing steering!

Too many Guaras plunged down will reduce the impact from a lonely steer-Guara (your "tiller-guara"), reducing the influence on the common CLR = Center of Hydraulic Resistance, as together with the CE = center of sail decide and define the pointing. That seems rather logical, that with the same men on board and with same mind for keel-supplement, we suspect that overcrowding phenomenon to be the killer of Kontiki2 expedition 2015. They couldn't beat to the wind and steer back to SouthAmerica, and tehrefore they vanished out in the South Pacific 1200 kilometers south of Easter Island.

As comparation we have the first Tangaroa as 1965 passed the dangerous Tuamotu Archipelago of French Polynesia by own means - steered by three Guaras only - one in front and two aft.

Many things seems to indicate:
The Kontiki2 rafts could have lifted up their front Guaras and eliminated the steering problem

Learning from the real life:
In all relations in your life that is your RESULT as count - and not your promises nor your intentions.
This rule is valid in all case of life - too for rafters. The question you will get is always:
Did you make it, did you reach your objective? - or did you not?

[ img - mail-kly-runasimi.gif ]

Lima - March 2019 - Eleventh edition of this page