Incas' oceangoing Balsa Log Raft

Essence = Synopsis = Summary

The result of our Guara research

The Kon-tiki raid of Thor Heyerdahl 1947 gave inspiration to many other primitive boat expeditions on the oceans of which only a part succeeded - and the rest did not.
Heyerdahl re-discovered the Inca rafts steer-system as since the Spaniards' first surprising meeting with a raft, has been something of a mystery for the european newcomers - they didn't understand how it worked. Obviously it still is a mystery, because none of the rafts as sailed out in wake of Thor Heyerdahl have returned to their port of departure.
With the last two rafts lost on sea, the decision was made to produce a manual for raft skippers: How to handle and how to use Guaras - and that is what is done with this publication.
If there are any relation between the existence of Guara-steering in Asia and that of South America, we don't know, but that may be a theme for a next "Heyerdahl investigation" of migration over the same huge ocean.

'Balancing of the Sidesliding' is all what a raft sailor need to know

We found two Guara explications:
1): The 'Balanced Sidesliding', where a craft with wind abeam balanced the leeway of aft-end versus that of fore-end.
This simple explication was mostly developed for in-line Guaras placed along the central balsa-trunk, but showed up of great general value for the most sail powered boats.
2): The 'Weather-cock principle' is where we on the broad log-raft utilize the cracks between trunks all over the raft - and obtain more stability of pointing.
By plunging down Graras in that way, may give a more stable pointing in relation to wind gust and big waves. That is so, simply because with Guaras in cracks more to windward we could obtain larger horizontal distance from the 'pivot point' = CLR to the CE = 'Center of Winds Effort'. And this CE will as usual blow leeward of the hold in water of craft = the CLR.

The hull of every sail-powered vessel (inclusive a Guara raft) has to be designed with high lateral hydraulic resistance - and low forward ditto (and that means in general: 'streem lined'). Thus neither any outer keel nor fin is needed.
The value of a TRIMED boat is obvious, as any board or Guara set down and/or a rudder or steer oar angled out to correct a wry pointing - will throtle the speed through water - slowing down a headway.

Around the sails
CE as Center of winds Effort is strictly bound to the canvas. We are sorry about only to have a superficial knowledge of kite-boarding, but at least kite + board seems to follow the general rules of interaction between sail and hull
(and we don't know anything around "Flettner-sails")

Whatever you have of rigging, the task of a sail is to divide the force of wind in a lateral and a forward directed force.
The lateral force from sail together with the wind on hull and rigging is up against the high lateral resistance of the underwater-hull, and the result is the leeway - as hopefully is low, exactly because the lateral resistance should be high.
That is the forward aimed force as push the vessel ahead, and the vessel will accelerate until the generated forward resistance of hull match the thrust from sail.
The relation between forward hydraulic resistance and hull speed is rather complex, and is normally defined empirically by hydraulic tank tests, as did the Kontiki2.
Of course the same hydraulic rules are valid too for the leeway movement - and with same complexity.

Summary of Guara steering:

Use your Guaras to place your CLR - your pivot point - where you want it,
and the wind will blow the Centre of Wind CE leeward of this Center of Water Resistance CLR
and thus point your raft
- and if your sail is adjusted for this pointing, you are sailing -

If you are in doubt, how wind and sea work together their centres CE and CLR
- then ask a wind-surfer.

He has no rudder other than a fin (a Guara) aft -
moving around and balancing CE and CLR is what he use for surfing -
and the rules for his wind board are the same as for your sail vessel.

Incas' sail powered Balsa Log Raft

The core of sailing by Wind

The pointing of ANY sail-powered vessel:

As an extension of those two named "Guara-theorems" we discovered the general relation between the two centres CE and CLR, and found that it is those two point of attack for the only two present natural elements as determine the pointing of any sail powered ship - and overall seen, we steer by influencing on position of this two centers by using rudder, Guaras, sail etc - - -

CE and CLR is a scientific way of looking at the steering of sail vessels, as we don't use everyday. We normally rely on and talk about the rudder position and balance of sails - and nothing more fundamental. But CE and CLR is used in mainly technical considerations by design of sail yachts.
By setting sail and plunge down some Guaras skipper adjust his CLR, and he can point the raft all the compass around - because the wind will blow CE leeward of CLR.

And talking both dynamic CE and dynamic CLR

The rule is simple:
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The wind will blow CE leeward of CLR
- and if your sail is adjusted for the now pointed course, you are sailing -

That means, that where a ruddersystem normally need a helmsman as continously control and correct the course, a Guara-system doesn't have this need.
It is a great self-steering system, where the raft herself act as a wind vane, making very stable autocorrection in relation to the wind.
The crew could be ocupied by other - as go fishing for their next meal.

One thing is pointing, but that is the forward headway as together with the lateral leeway define the true course over the ocean.

Sailing ahead, the bow is pressed into the sea, and in that way side-sliding of fore-end is restricted. More forward speed = more restriction.
Sailing speedy ahead a skipper therefore can use more foresail - and a raft skipper, as normally has no foresail, he now need less front-Guaras and can therefore lift those upwards, as they only brake the headway.

When sailing with wind abeam the skippers on sail crafts often are talking 'weather helm', even if that is their aft-end as slide sideways with wind - or more scientific we could say:

Sailing-on, the water press onto lee bow is influencing on the position of CLR, as move ahead, but fortunately it is followed by the CE as too move ahead, due to the sails are sheeted out and perhaps too heeled. Playing together so, the sailing will only need minor adjustments of Guaras - or angeling of rudder.

A trimmed vessel is neutral in her steering, when sailing with wind abeam - even a rudder-steered vessel. If not trimmed, skipper has to activate her ster-system.
Any trim on any sail-powered vessel (on rudder-steered crafts as well as rudder-less sailers) is fundamentally done by adjustments on CE or CLR - or both.
Logically it must be so, because wind and water are the only natural elements, as yield forces on a sailing vessel (Newton's third Law) - and they attack of course in their own centers.

Speaking figurative:
The wind will always blow its center of attack down to lee of the crafts hold in water. Thus in that way the actual two centres CE and CLR together will define the pointing of the vessel!
We could say that your boat is stretched out (or suspended) between its CLR and its CE, as thus define the pointing - and heeled (those who can heel), even more evident!

A "laundry line" between blow of wind and resistance of water to make you remember CE and CLR as the attack points for wind and sea
- and that is those two "attack points" as define the pointing of your craft

You steer your craft by a rudder, as push on the streaming water
- or you steer her by a dipping oar or Guara, as balance the leeway of aft end against that of for

blowing of wind

close reach [ img - suspend-dinghy.png ]

DINGHY

broad reach
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LONGSHIP

beam reach
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CATAMARAN

running

LOG-RAFT

resistance of water

- but whatever you use to steer, you manipulate the position of CE and CLR
- as said:
that is the position of those two centres as define the pointing of your sail powered vessel

il powered boats are suspended /stretched-out between wind and sea - just as these examples shown here

Any board or Guara set down + and any rudder or steer oar angled out - will brake the speed of headway

sailing wind abeam

The 'Patín a Vela' = 'Patín Catalán' is a class of boat, as is shaped as a double hull dinghy. It is interesting, because she is born without rudder nor Guara. The Patín Catalán is steered by moving CLR = relocating the weight of crew (1 man) and adjusting CE by sheeting in or out.
With an open deck as banks all around the mast the sailor can place his weight where he want - and the boat will react.
Note right photo: The sailor have moved his weight (CLR) to extreme aft, and the wind is just now blowing the CE to lee of that - and the patín is turning.

The laws of nature for this patín (patín in Spanish means skate in English) are the same as for any sail powered vessel.

turning around a way-point

Small vessels you can steer rudderless by moving around your body. By bigger boats, the weight of own body isn't enough.
Rudderless sailing, wind surfing and kite boarding together with the Patín Catalán, are all the active sport verification of the thesis:

The wind will blow its center of effort down to lee of center of hydraulic resistance

- and pointing of the "vessel" is defined by those two centres -

Incas' oceangoing Balsa Log Raft

One page Manual for Daggerboard rafts

the Steer system for Rafts

Daggerboard steering we call it in English = Guara- Vara- or Barra-steering in Spanish. (nobody knows right writing)

As the world have developed, the rudder /steer-oar is nearly universal, and it is a realy well developed steering gear, as has resolved our steer problem in hundreds of years, at least if it has sufficient forward speed to make it work. Forthermore a rudder too is useful for motor-powered ships.

The characteristic propperty on Inca rafts is their daggerboard steer system, where they balanced the sidesliding of aft-end against that of fore-end. Too the Pharaohs seems to have employed that principle on their reed boats 5000 years ago.

With 4 daggerboards and the sail adjusted for the pointing, you can handle your raft without rudder.

As named: If you on a raft place 4 daggerbords two and two for and aft along the central trunk or place them in the corners, then you can move around with your CLR=Center of Hydtraulic Resistance - (move it from for to aft - or all around the mast).
The position of CLR in relation to CE of the sails is what give the pointing of your craft. Note that is fundamentally the same as a rudder do, even if we only are talking angling the rudder and never have talked moving a CLR.

As we know, the incas plunged the daggerboards down between the logs where they needed. The Egyptians dipped their handheld steer-paddles on lee side. Building a special holder for the daggerboard or just plunging down between the trunks, the only inconvenience I see is, the chance to break a vertical fixed daggerboard, when a big wave knock the raft sidewarts.
The place where to raise a mast depend of which sail you choose. That is the CE as count.

If instead of daggerboards along centerline, skipper plunge the boards down in a wind-side crack, he will obtain more stability of the pointing. He still has to balance the aft-end against for-end to keep his course.
If skipper use lee-side crack for his daggerboards, the only inconvenience is, that he need more activity from helmsman to keep the balance stable. Note that the old Egyptians used their paddles, sustained to lee side, as reed-boats have no cracks for daggerboards. Each helmsman with hand on own paddle. There are seen pictures with up to 5 helmsmen standing side by side.

the Hull for a Raft

The raft hull you can build as you will - using balsa logs, pine trunks or sealed plastic or steel tubes, as too has been employed. A raft is a flat bottom vessel to land on a beach. A pointed bow, as divide the bow-wave in two is useful, but not a condition. The daggerboards can compensate.

The most important property is, that the hull hold a HIGH lateral hydraulic resistance - and a LOW forward ditto.

Without this relation, there surely will be difficulties to tack against wind. Note please, that "the daggerboards" is a steer-system and not a keel-supplement. The "keel" is the long straight side-log.

The lesson from the Incas is, that with 4 daggerboards along the central trunk a raft-skipper can move his CLR from for to aft and thus balance the leeway independently of the two ends. And the same will work on any sail-powered craft, where we can mount more daggerboards (trim-boards) - and doing so we don't need any rudder nor steer-oar.
(Perhaps an useful information to some later reed raft sailors)

If you have to drift to survive a gale, you neither need storm sail nor drogue - that feature is build in by the Guaras. Plunge down the daggerboards in that end of raft as you want against the wind - and the gale will blow the raft with hut and mast down to lee of the daggerboards - with or without reefed sail.

the Sail for a Raft:

Whatever you want to use of rigging we distinguish two situations: 1): sailing with wind abeam - versus - 2): running for the wind.

Any other wind direction we consider as a combination of those two. And therefore it is those two situations we analyse beforehand on any design of a craft. For all winds the general rule is valid: The wind will blow the CE down to lee of the CLR = the hold in water.

Hoisting your sail, it is the CE=Center of winds Effort as is important. You can combine CE with more sails or you can hoist your lonely sail: The CE will blow downwind of the of CLR= Center of Hydraulis Resistance - both in static and in dynamic situations. The result define the pointing of your wessel.
If your sail is adjusted for that pointing - you are sailing.

Note here please, that "adjusted" means in relation to what you want to do: If you want another type of "sailing" such as heave-to or drifting slowly sidewarts hauling a dragnet or drifting to a quay - it is still the two centres CE and CLR as define the pointing of the craft, as there is no other force present (except perhaps a current or if you employ rowing or towing or similar).

As explained in the chapter #6:
The task of sail is to split the winds effort in two. A longitudinal force to push the boat along + and a transversal force as we can resist with the lateral hydraulic resistance - as hopefully is high, for which reason the lateral sail-speed (the leeway) therefore is low.
A square sail is probably the most original Inca, but we have seen many types of sail mounted on log rafts.

A sail is mostly adjusted by sheeting-in versus sheeting-out, in such a way that the sail is dividing the angle between the apperent wind and the course of vessel. The course of vessel is in general considered as the 'pointing' of centerline, but here was the error of last raft raid: sailing with a square-off stem, because she sailed along a diagonal. If skipper had realized that, he could have done one of two: 1): either corrected the diagonal course to the centerline course by adjusting his daggerboards (more daggerboards down aft to counteract the one-side deflected bow wave) - or 2): he could have adjusted his lonely sail to divide the angel between apperent wind and the sailed (diagonal) course. He didn't neither - and lost his rafts.

Recomendation: use the type of rigging as you have practised to handle earlier
- and chose a sail type, as you can handle (inc. reef) from deck -
But most important of all: Take a test sailing around the nearest island, before you head out on the huge, waste and empty ocean.

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