Carbon layup for a rudder and daggerboard

[usa1154]

I'm thinking of building a new rudder and daggerboard for my I14. A friend has a CNC milling machine and has offered to machine the cores for me, but I really don't have a good idea of how many layers of carbon to use. I assume that I'll have to use unidirectional for most of the layup. Would I have to use uni at 45degree angles for torsional strength or could I use bidirectional cloth?

Does anyone know a good book I could buy on the subject?
thanks,
jack

[Karsten]

It's not that simple unfortunately. The cores could also fail in shear so you would have to check that as well. Then there is the question if the foils are stiff enough if they are strong enough. This means they might not break but will be too floppy to be fast. That will also require extra carbon or you have to switch to high modulus fibres if you can get them. If glass foils have no stiffness problems your carbon foils will have enough stiffness. Although if you are light and sail in gusty conditions a flexible centreboard might be better. They tend to deflect in gusts and therefore the boat is easyer to handle.
Torsion is probably not a problem even for the rudder. You can just use a layer of cloth wrapped around the whole foil at +-45 or unis at +- 30 degrees. That should do the job.