Hi Don, Replacement bungee cord for the M15 rudder is available at any marine store - by the yard. Check the diameter of what is currently in place and buy the same size. Tension is a try-it and see proposition. Install it. With knot on one side, pull some tension on the bungee and tie it off, and give it a try. If not tight enough, repeat, and tighten some more. T'ain't hard to do. Connie ex M15 LEPPO