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 case of the 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 - 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 reason why

Their old raft Tangaroa-2 10 years earlier, they have sailed perfectly. Their actual calamity seems to come together with introduction of the square-off bow.

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. We have still not received any final report from the expedition, and will probably never get it.

Photo of 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 stay on Easter Island.

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

The Message from raft "Rapa Nui" of Kontiki2-raid together with the later air-photo picked up from their own web-site: gave us the kick to try to find out, why. Gave the impulse to this research: Investigate the general theories around Guara-steering, raft sailing, hull shapes and sails, as it is described in details on the anterior web-pages
[ 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 reckless start
- and the irresponsible was, that they sailed out without previous test of their new creation -

The lesson with hindsight - years after the happening
The understanding of what could 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.  

My actual conclusion: Being experienced members from Tangaroa-2 raid as sailed Kontiki2 - they, in their eager to get much 'keel' to beat higher, could have brought that over-crowding practice with them, and that is what I judge as most probable.

the preparations before start

Pre-analysis to choose square-off hull shape

The first suspected for 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

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 draw by different speeds, because that was what they were 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 of 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 side trunk, the raft-shape met the conditions for being powered by sail:

The condition to power a vessel by sail:
A wind powered sailship is characteristic by her LOW forward hydraulic resistance
+ in combination with a HIGH lateral ditto.

[ img - Compass_Rose.png ]
The common rule for pointing a Guara raft is demonstrated earlier:
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 -

the scrutiny of that air photo
The rule demonstrated earlier:
You can control the pointing of our raft all the compass around - with your Guaras alone
therefore the difficulties for these Guara-steered rafts of the Kontiki2 raid exclude the Guaras for blame
If a raft can't beat to the wind, it is NOT a Guara-problem
- the problem is either the Sail or Seamanship (knowledge)

- and what was it, we saw on the photo -

The first view
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

Detailed drawing

[ img - RaftOnOcean-60.jpg ]
the sail is adjusted fair, if the raft was sailing along the center line, as they do where this Nordland rigging comes from
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°)

The rafts with a tricky transom bow

Compairing with the 10 year earlier Tangaroa-2 we assume, that the calamity came as a consequence of the square-off bow. Therefore a look on transom bows.

Square-off rafts are not unknown in our heritage of drawings, even if the verbal descriptions say: shaped like a hand with the biggest trunk in center.

[ img - Ulloa-raft-1736.jpg ]
Juan & Ulloa - 1793
[ img - sq.raft-unknown-origin.jpg ]
unknown source
[ img - Radeau-Guyaquil-1810.jpg ]
Alexander von Humbolt - 1810

The nature of bows, if no counteractions 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 stay sail.

And in a technical language that means: either draw backwards the CLR - or move ahead the CE - to keep their downwind relation in same line.

the 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
the square-off raft will sail-on along the diagonal and thus divide the in-streeming water
+ 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 side
With sketches of water streaming against the bows of two comparable flat-bottom rafts, we 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 on the square-off bow wave. .

Steering a Guara raft is in both cases: Balance the leeway of aft-end with that of fore-end. The square-off raft only need more Guaras down aft (or alternatively a permanent fin keel or skeg mounted aft to compensate).

we are NOT accustomed to mount rigging along a diagonal

Struggeling with square sail rigging on square-off raft

"If the sail is adjusted - - - " exclaim the raft-rule

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 is where the Norwegian raft sail adjustment went wrong 2015
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

the MAIN-RULE for a square sail is that it (the yard) has to divide the angel between the apparent wind and the true sailed 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.

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 as all their square rigged boats has done the last thousands of years in North.

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

[ img - pointing2.png ]
Counter #1
[ img - pointing3.png ]
Counter #2
[ img - pointing1.png ]
Counter #3

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

Notes about counteract options

Counter #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 against the centred 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
When their raft is pointing as they want, they can optimize their sail adjustments.

With other words: set down AFT Guaras to balance sidedrift of AFT-end against that of fore-end.

Counter #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, 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 solution.

Counter #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 kill the steering:
Real seamen is expected to handle any floating vessel
A real seaman is expected to navigate any body as can float on the water?
[ img - seamanship.png ]

- means the skill, techniques, or practice of handling a ship, a boat or any floating item 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 counteract - 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 trial of their new ship-construction before sailing out on a monthlong raid.
The well established "prøveseglingsprosdyre" = 'procedure of test sailing' described by Jon Godal, they left out.

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

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

The great historical question arise after the hard experience with this raid: - around the need for experienced seamen.
If Tupac Yupanki as native governor from the mountains really sailed out on the sea with 2.000 or perhaps 20.000 men and soldiers on lets say 100 or 1000 rafts, he at least should have one experienced sailor on board each raft. And from where could he 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!

An Overkilled 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 - but no - they sailed out on the ocean and lost their rafts.

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

This photo leave the impression, that Tangaroa-2 on her west-going raid never sailed with wind abeam
Overcrowded? = Overkilled!

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

- but did Tangaroa2 never need 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 navigators 10 years earlier.

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.
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.
And with the same men on board and with same mind for keel-supplement, we suspect that phenomenon to be the killer of Kontiki2 expedition 2015. They couldn't beat to the wind and steer back to SouthAmerica. They vanished in the South Pacific 1200 kilometers south of Easter Island.

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 - December 2018 - Tenth edition of this page