John,
My concern was that the hull in the vicinity of the groove was flexing, allowing the bolt rope to escape. That's why I was thinking I needed to add material to the hull to stiffen it up. Although, when I got the boat, it was already pulling out, and I didn't really investigate why, I just wanted to make the boat functional.
So maybe I don't need to add thickness, just increase the bolt rope diameter? Can you describe how you enlarged the feed opening?
You might have saved me a bunch of work, thanks!