Jamie wrote:
The plywood-carbon fiber on the other hand would be well in my comfort zone. Is anyone able to say about the strength of it? We’re talking about a 1600kg 22ft monohull with a large junk sail and a larger rudder than the original plus I’m moving it some 40-50cm aft to the transom.
This is where someone with some engineering knowledge would come in handy. When building my rudder fittings I aimed to equal the thickness of the designed stainless steel fittings, which was 4 mm. Given that carbon fiber is supposed to be as strong as steel I figured I was in safe ground. It took a lot more layers of carbon than I expected to build up the thickness. I used a mix of woven cloth as the first and last layers, and then some double bias for thickness buildup, and some unidirectionals for strength. If it were me I would aim for a thickness of 6mm for the transom brackets, probably about 8 mm bolts for attachment to the transom, and 12 mm through bolts for the pins. I think I would want the thickness of the flanges on the rudder to be at least 50 mm with probably at least 6 layers of unidirectional carbon fiber wrapped around them. I used a proper laminating roller for laying up the carbon, and I used peel ply over the final layer to give a smooth finish.
Certainly if you can build the rudders then you have the skill to make carbon rudder fittings. It probably does not need to be carbon fiber, but if you just used normal glass cloth to make these the fittings would need to be so much thicker to get the strength.
If you build in some balance area on the rudder blade forward of the rudder gudgeons you will decrease the load on everything and the boat will be a lot easier to steer.