Thanks Nick.

The info and links you provided helped me understand why the tiller arms are bent where they are. I suppose you would have to map the minimum turning path to determine the exact difference between the inner and outer hulls. This would determine exactly where to point the tiller arms.

I guess that different speeds would give different turning radiuses so there would have to be a certain setting that would suit one speed with a tolerance each side of this. I also assume that in light winds the adverse effects of the chosen setting would be minimised through low flow around the rudders and minimised drag. Converserly at high speeds the number of skipper errors and conservation of rig, sail body and soul would tend to outweigh having a precise tiller angle setting.