Roof Rack Canoe Gunwale Bracket

Last weekend, we had a canoe sliding around on my friend's kayak/canoe trailer. It's a really nice setup with 1 1/4" aluminum tubes but the two canoes on the top had a tendency to slide to the sides. These brackets slip on the horizontal tubes to prevent side to side motion. Years ago I had a Yakima roof rack and was amazed at the improvement with gunwale brackets.