Casa
de
Dina
[ img - tumi2.gif ]
Hotel
in
Lima
First edition of this note
[ img - incaruna.gif ]
INCA
RUNA
[ img - raftlogo.gif ]
SPROG

Inca's Balsa Log Raft

Sailing catamarans with Guaras

 

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

[ img - pahi63-profile+centerboards.jpg ]
the interesting is that this catamaran is born with four centerboards

[ img - pahi-63.jpg ]
placed as trimboards in the ends of each hull

Instruction:
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 fundamental rule for floating bodies exposed for wind is:

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.

[ img - pahi63-profile+CLRs.jpg ]
CLR means 'Center of Lateral Resistance',
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.

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

 

On every free floating craft:
the wind will blow 'Center of Effort' leeward of 'Center of Lateral Resistance'

[ 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 ]

Two warnings

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-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 -
KLAUS LYNGE

 

[ mail: kly@pusac.org ]

kly-note written february 2017