They have several different names. This boat’s designer called then guards. Others call them gunwales, or sometimes rails.
They weren’t hard to do. Many people like half rounds. The designer suggested half 8-sided because he has no router. Neither do I, and I like the looks of the half-8-sided.
These are made of Sitka spruce, absolutely delightful to shape. However, part of getting the right shape is getting the shape right. I’m fairly adept at planing something that is parallel to the bench top.
I’m not nearly as adept planing a 45 degree surface. After a bit of fumbling, I put a good 45 degree surface on a piece of poplar. It was then cut into about ten small chunks and glued with rubber cement to the qunwale. That positioned the workpiece for easier planing. Pop off the props and refit for the opposite surface. Easy.
Attachment is with ring nails. Bedding is Dolfinite, a tan colored material with a consistency a bit stiffer than peanut butter. The only mishap was dropping one of the guards immediately after buttering it with Dolfinite. Of course, it hit the floor butter side down. Dolfinite cleans up rather easily with mineral spirits.