Added Strength Under Cap

[LandscapeSavannah]

I’m not a new boat owner, but I’m a newer SeaCraft owner. I have a 1976 20’ and someone began a transformation by adding an Armstrong bracket and closing the transom. I was wondering if there was a way to strengthen the space up under the cap? There is a large amount of flex when a passenger steps onto the side of the boat when boarding and I figured this would be a good area to practice working with fiberglass. Any recommendations?