It's starting to look like a rudder! The rudder bow is now screwed and riveted to the rudder spar.
But before attaching the rudder bow, I formed the top of the 1" rudder spar to fit around the 1/2" tubing. That entailed inserting a 1/2" bolt in the slot and hammering lustily on the rudder spar.
I began with a few tentative taps of a rubber mallet, followed by several brisk strikes that were equally ineffective, I dug out the shot filled 2 pound dead blow hammer and relieved some aggression. 1" x .058 aluminum tubing is sturdy stuff and does not submit willingly.
Once the top 6 inches of the spar were tapered and the sides of the slot trimmed and folded around the 1/2" bolt, the fit was checked, an 1/8" hole was drilled opposite the 1/2" hole at the bottom of the spar, a pilot hole drilled into the dowel and the bow secured with a 1" wood screw. Then back to the rudder grid board for final positioning of the bow, drill and ream holes through each side of the spar into the 1/2" tubing, pull a couple of rivets and the rudder bow was secured.