I don't recall Rare Bird ever requiring any noticable helm angle on either rudder to steer straight. (Col, maybe we can take some photos when it is sailing again, hint, hint). Nor does my El and the others I have built. This is one of the first things I check, a hangover from all the flak I got in the early days about the impossibility of such a set up.
In the video at http://www.youtube.com/watch?v=8chR6DAFjGA the rudders appear to be fore and aft (from memory, the front steering lines had jumped off so it was locked fore and aft), although there are no head on shots. The aft rudder wake appears to line up with the front rudder wake, which may imply that they are both pointing in the same direction.
On RB turning with the rear rudder while sailing to windward in 15-20 knots was like putting the brakes on. Helm would load up, there would be a big valley on the windward side, a corresponding hill on the lee side, exacerbated by it's nearness to the hull, the wake width would widen and the boat would alter course very slowly. Lock the aft one straight ahead (like a daggerboard) and turn with the bow one and it would alter course quickly and with no fuss.
I will be very interested to see what difference the longer, thinner rudders make on Ono. The standard ones are 1.5m deep (immersed) x 0.5 wide NACA0012. If you can go this big, you should be able to eliminate the daggerboards.
Have you got any photos/description of the steering set up you are using? If you do build new ones, be aware that the amount of carbon required for strength goes up proportionally to the square of the thickness and for stiffness by the cube of the length. Let me know if you need any specs or materials for new blades.
regards,
rob
__._,_.___
.