Inca's Balsa Log Raft
Sailing catamarans with Guaras
This 4 boards are more than for TRIM - it is 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
The basic idea in Guara-steering is the fact, that on a floating body CE = 'Center of Effort' allways will blow leewards of the CLR = 'Center of Lateral Resistance'
(That we of course can jam by adding other forces, as throw out a drogue, set down an oar, start a motor /truster or influence the sailing with a classic rudder.)
The fact is, that with four centerboards on a catamaran we can change the underwater-hull and move her CLR = 'Center of Lateral Resistance' around - all the compass around the supposed CE = 'Center of Effort' of wind on sails.
The CE = 'Center of Effort' is represented by the center of sails = the center where the wind attack, and this is in every moment dependent of the sails you are carrying.
The wind will try to blow her CE to leeward of CLR (her hold in water)- and there she will stay until the wind change - stable as a weathercock in the wind.
We have heard of skippers steering with wind-rudder, as usually is a wind-vane attached by ropes to the tiller and moving the classic rudder of the boat. And the boat will keep its course in relation to the wind
I don't expect, that any catamaran-skipper, as hasn't done any wind-steering before, will release his tiller and jump 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
Finding your CLR in practice:
The CLR is the pivot-point for your craft = her hold in the water. That means that 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, we move forward the CLR - and give by this the stern an option to flow with the wind.
If we otherwise lift the front centerboard and dip down the aft, the CLR move backward and we permit the bow to correct our course by floating with the wind.
Guara (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.
they make a steer-system
On every free floating craft:
the wind will blow 'Center of Effort' leeward of 'Center of Lateral Resistance'
Guara steering will only work with wind and sails - and not with neither paddles, oars nor motors -
Setting down the two centerboards in lee-side too is possible, and they will work as common leeboard.
The only thing you have to pay attention is, that a LEEBOARD need to be steered by a rudder and streaming water, whereas LUFF-BOARDS will keep a stabil course without need to tuch your tiller.
Greetings from Lima in South America, where nearly no sail craft is present on all the pacific coast -