Spruce and Ipe back bracing. I've done back bracing very similar to this (with results I've been very pleased with) using carbon fiber on top of spruce. I decided to do this one using all wood on the back braces. I chose Ipe for its extreme stiffness. These braces are arched by laminating them in the radius dish. They maintain the 15' radius dome of the back extremely well. They are beveled at the ends and stop short of the linings. You'll see that better when I have the "boat" done.