The correct term for that bar is "rudder shoe". Your post doesn't state where the missing bolt is, and the size of bolt is determined by how the manufacturer constructed the shoe and how it's attached to the hull and rudder. On my Nordic Tug, the shoe is thru-bolted with 3 bolts through the hull (circled in red), and the rudder post rests in a bearing at the end of the bar. First picture shows the shoe where it's attached to the hull. The bolts and nuts are covered in a layer of BoatLIFE caulk. This picture was taken when I damaged the prop hitting a rock. Also shows how Interlux Trilux bottom paint failed in fresh water (boat is docked up a fresh water river). Second pic is after the prop repair and I'm ready for spray painting the prop with Rustoleum cold galvanized paint. You can see where the bolts are capped with BoatLIFE Went back to Pettit's Hydrocoat on the shoe and rudder.
