I've got oak dowel masts, with carbon fiber tubes for spars/yards. Now that I have the lathe, I can turn the masts for tapering
I used birch dowel rods for masts and yards. The masts were chucked in a drill and tapered with sandpaper. The yards on the Requin where two slightly flattened dowel rods lashed and glued together.
I used 1/4" carbon fiber for Constitution and Victory's masts, but those are smaller-scale ships and I used cantilever masts for simplicity. On my 1:48 Constitution (planned), I intend to use scale size wooden dowel, about 1/2" thick. That should be plenty strong enough, especially if I add some stays for extra strength. It's amazing how much strength a little rigging can add. For yards, I plan to use 1/4" (topgallants on up) and 3/8" (courses and topsails).