Very interesting thread. When I was looking for a boat I saw a First 40' here in Fajardo PR that had badly corroded keel
bolt nuts. They would crumble just by touching them. I contacted Beneteau
and they told me that the studs were stainless steel
and the nuts were galvanized. That made sense since the studs looked perfect. It was just the nuts falling apart. You can replace them one at a time.
In my First 456, the keel
was removed by "accident" after hurricane
Hugo. Theese boats had a reputation of weak keel to hull
joint structure. So the previous owner had the lower hull
structure reinforced from the inside of course and the keel was reinstalled and attached to the boat with new 316SS bolts and nuts. As an extra meassure he ordered custom 316 stainless steel
5/8 inch thick angles to provide extra support from the inside. The bolts go through the SS angles which are also attached to the inner structural elements of the hull. From an engineering point of view it is overkill but it is very nice to open the bilge
and see such a strong structure holding the keel.