I second what Mark said about epoxy and threaded rod. This is an awesome repair technique for lots of things, not just rudders. You drill a hole just a little bigger than the rod, and fill it partially with thickened epoxy, then push the rod in. The epoxy of course grips the wood, and it also grips the rod because of the thread. A smooth rod wouldn’t work nearly as well. I have used this for many repairs.
