The design space for the rudders opens up when combined with a centreboard.
The rudders do not need to be sized for leeway prevention. With a balanced rig they will do very little work. Their size is governed by their ability to survive a hit. Their contribution to drag is low so if they are ventilating or not it does not make much difference. The leading one under the hull is prone to ventilate anyhow.
A possibility would be to use two dipping rudders at either end preset at about 5 degrees or more. Essentially there is no rudder drag and nothing to foul most of the time. As soon as the rudder is lifted clear any fouling drops off. Most of the steering could be achieved with the rudders immersed shallower than the bottom of the hull. The steering force is a function of the level of immersion.
This is the solution I have used on my pedal boats to avoid fouling and damage when hit with logs. I use different methods of operation. The simplest is control lines to immerse and spring return but I have also made a simple counter-rotating gearbox so one rudder lifts higher as the other goes lower. Rob has seen both arrangements.
This shows the counter-rotating set up:
There is a 6mm diameter shaft from the starboard grab handle to the rudder box to control the immersion. Similar to any ventilating rudder they deflect water to produce the steering force.
A counter-rotating box could be set within the end of the hulls with the shafts coming out not too far above the waterline on either side of the hull. Only the trailing pair would be used unless in a tight space or possibly during a shunt. The box could be outside the hull but then it presents more resistance when forced through waves. If hit the rudders are free to rotate upward against the applied control force.
Rick Willoughby
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