How are the original bolts anchored to the (various) keels?
The bolts used to anchor
the frame of a house to the foundation are L shaped and set into the concrete. The L prevents the bolts from turning.
I would imagine that keel bolts
could be set into a poured keel
...assuming that it's not hot enough to melt, distort or weaken the bolts using the same L type bolts. Removing them and replacing them is another story.
To replace a bolt in a keel
one would have to drill and tap it, it would seem.
My keel bolts
(16 in all) are encased in GRP and not visible except as huge bumps in the bilge
. The keel is cast iron and it has a flange about 1" or more thick and the bolts are located in the flange about 4" to port and starboard of the CL. I don't know the material but I suspect they are tapped into the keel flange and then ground down flush to the feel which is then all covered with fairing. The location of the bolts appear at athwartship hull
reinforcements which I presume are either steel
belts or some other additional GRP layup
to stiffen the hull
which is about 3" thick at the keel location.
If I were to replace them, I would contact the builder
and find out what they are and how they would replace them and purchase
the bolts from them (most defintely metric). If I am correct in how this is constructed, I would not drop the keel, but remove the bolts one at a time (on the hard), remove the fairing, install a new bolt, grind it off flush and then seal and refair and then glass over the bolts in the bilger again. YIKES what a job.
This is what they look like from the bilge