Suggestions for reinforcing Kevlar canoe floor

I recently got my hands on a 30 year old kevlar canoe that needs a little love. The most pressing issue to me is that when two people are in the canoe, the bottom flexes up in a fairly asymmetrical manner. I'm not seeing any stress lines in the floor of the canoe and there aren't any obvious weak areas in the hull. Has any one here been successful at reinforcing a composite canoe floor either with a rib or additional layer approach. Any help would be useful.