Inca's Balsa Log Raft
Sailing catamarans with Guaras
Some catamarans are born with Guaras - even if they call them "trimboards"
placed as trimboards in the ends of each hull
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 at page #5.
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.
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.
and thus define the pointing of the craft
- and if sails are adjusted for the now pointed course, you are sailing -
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.
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.
and here we are talking exclusivamente the wetted surface of the Hull
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.
they make a steer-system
A Guara-steering = centerboard-steering work only with the wind.
While the wind attacks in the CE-center of sail trying to blow away your vessel, the water will hinder this, seizing your boat in the CLR-center 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.
the formost 100% down and the aft the half will move the CLR forward - and the cat will point more against the wind
we can move the CLR all the way around the CE
Guara steering will only work with wind and sails - and not with neither paddles, oars nor motors -
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.
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.
Greetings from Lima in South America, where nearly no sail craft is present on all the Pacific coast -