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Fifth edition of this note
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Inca's Balsa Log Raft

Sailing catamarans with Guaras


Some catamarans are born with Guaras - even if they call them "trimboards"


[ img - Pahi-52-sailing.jpg ]
oceangoing catamaran of renown mark (Wharram)

[ img - pahi-63.jpg ]
the interesting is that this catamaran is born with four centerboards,
placed as trimboards in the ends of each hull
[ img - pahi63-profile+centerboards.jpg ]

Instruction:
Those boards are installed for TRIM of the cat - but together the 4 boards are a steer-system.
That means, that a catamaran with four centerboards don't need any rudder. The skipper can take those rudders totally away and steer by Centerboards only.
- and those prehistoric steer technologies are explained in details in the chapter of 'Daggerboard Navigation'.
The basic idea in Guara-steering is the fact, that on any floating body CE = 'Center of Wind' allways will blow leewards of the CLR = 'Center of Water Resistance', as is the central hold in the water - and that is so, because there is no other forces influenting on the boat.
The rudderless sailors are mostly moving around the CE of their sails while the Guara-raft skippers are changing the underwater-body and thus move around their CLR.

Rule for Guaras (here 4 centerboards):
By use of your bow and stern Guaras, you can dominate the pointing of your vessel

The fact is, that with four centerboards on a catamaran we can change the underwater-hull and move her CLR = 'Center of Water Resistance' - all the compass around the supposed center of wind on sails.
The center of sails is the center where the wind attack, as in every moment is dependent of the sails you are carrying.

The common rule for ANY sail-vessel:
The Centre of Winds Effort will blow downwind of the Centre of Hydraulic Resistance
and thus define the pointing of the craft
- and if sails are adjusted for the now pointed course, you are sailing -
- and so she will point until the wind change - stable as a weathercock in the wind.

That means, that by manipulating your centerboards, you can place the Center of Water Resistance where we will, and this together with the Wind-center will make the boat point.

The nacked truth is, that the AFT-trimboards are most important for Guara-steering, why the FOR-trimboards under sailing are replaced by the bow pressed into the sea, as therefor is hindred in sidesliding. Just as with rudder-steering we CONTROL the sidesliding of STERN, and not the bow.
Ref-1: the bowwave locking
Ref-2: the learning from Dirch

On every sail ship it is so, that because of gusts and waves the dynamic component defining the centres of both water and wind will oscillate and that make exact calculations of Center of Wind and Water Resistance impossible with any degree of accuracy.
Just as with rudder-steering we neither need to know that. We only need to know their nature to be able to counteract the actual situation by adjustments of sail and Guaras - and that is what skipper has to do.

We have heard of skippers steering with wind-rudder, as usually is a wind-vane attached by ropes to the tiller. And thus moving the classic rudder of the boat, the boat will keep its course in relation to the wind
I don't expect, that any catamaran-skipper, as not has tried any wind-steering before, will release his tiller and jump directly to Guarasteering - but if he do, he will experiment a more stable craft in relation to the wind - and of course I would be happy if a sailor will confirm the hypothesis by own experience on the sea.

[ img - pahi63-profile+CLRs.jpg ]
CLR stand for 'Center of Water Resistance',
and here we are talking exclusivamente the wetted surface of the Hull

How to locate your static CLR in practice:
The CLR is the pivot-point for your craft = her hold in the water. That is found, when a steady push or pull directly at that center will make the craft move sidewarts without tendency to turn.
If we dip down a front centerboard 100% and lift the aft, the CLR move forward - and give by this the stern an option to flow with the wind.
If we then do otherwise, lift the front centerboard and dip down the aft, the CLR move backward and we permit the bow to correct the course by floating with the wind.

Guara (old Southamerican word for the vertical boards between the balsa trunks), Daggerboard, Centerboard or Trimboard steering was used by the early southamericans from the time before arrival of the Spaniards, and it was continued for the sailing of Inca balsa rafts until the motors took over the propulsion of oceangoing cargo-vessels and professional sail-vessels disappeared.

[ img - pahi-63+.jpg ]
Four trimboards placed in the ends of each hull
they make a steer-system

 

Rule for every free sailing sail-craft:
The wind will blow the CE-Center [ img - CE4star-37.gif ] downwind of the CLR-Center [ img - CLR5-star-33.gif ]

A Guara-steering = centerboard-steering work only with the wind.
While the wind attacks in the CE-center of sail [ img - CE4star-37.gif ] trying to blow away your vessel, the water will hinder this, seizing your boat in the CLR-center [ img - CLR5-star-33.gif ] trying to keep her back.
In this way your boat is "stretched out" between those two centers by the force of wind and the resistance of water, and her pointing is thus defined.
Just as you can incline a picture on your wall by move its hang-up.

[ img - cat-N.png ]
1): Setting down both port centerboards will create a CLR in port side - and a Zephyr wind will make the cat point North

    

[ img - cat-E.png ]
2): Lowering the two aft centerboards will create a CLR in between them - and the cat will run for the wind

 

3): Diferentiating the boards:
the formost 100% down and the aft the half will move the CLR forward - and the cat will point more against the wind
[ img - cat-NW.png ]

    

4): plunging aft centerboard right down and the front only half will permit the bow to drift - and the cat will sail on in broad reach
[ img - cat-NE.png ]


With few drawings we have shown, that by playing with lifting and lowering of our four Guaras /centerboards,
we can move the CLR all the way around the CE

[ img - cat-all-stars.png ]

Some remarks:

1):
Guara steering will only work with wind and sails - and not with neither paddles, oars nor motors -
2):
Setting down the two centerboards in lee hull too is possible, and they will work as common leeboard.
The only thing you have to pay attention is that arranged so, the two boards in lee hull easily will place the CLR in an unstable position downwind of CE, and therefor need to be dominated and steered by rudder and streaming water. Against that, boards in luff hull will keep a stabil course without need to tuch your tiller. Luff is the wind-side - opposite lee.
3):
If your catamaran NOT is born with inside Centerboard-type trim boards, as the above illustrated Wharram Pahi, it could be an easier solution to mount these as leeboards outside on luff hull (what all together means on that side of the hulls, as turn against the other hull). With that your hulls at least will not need submit to any serious "surgical" operation.

[ img - cat-all-stars2.png ]

Greetings from Lima in South America, where nearly no sail craft is present on all the Pacific coast -

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Lima - Yule 2017