Cracked Stringers

[JohnB]

What your looking at is not uncommon, they didn't get enough glass into the corners/edges of the stringers. Actually, I have seen worse (yes in seacrafts).
What I did with mine was, grind the surfaces to get some clean glass, fill the cracks with thickened epoxys, put 3 layers of 6" biaxel tape on it biaxel and use epoxy to put it all back together. Make sure you offset the layers, so you don't create a "hard spot". It will be stronger than when it was made. I would suggest doing this the entire length of the stringer.

I am not sure how much strength the foam in those stringers has. When they made these boats, I don't think they were using the high strength foam that is available today. I believe the box of fiberglass around them is where the strength is in these old boats. In most of them, the stringer glass is no longer bonded to the foam. You could drill small holes every 12" and "pour" epoxy down the sides if you really wanted to go nuts with it.