I've had some various experiences. Bought several and built one GRP yacht with lead keels, had a steel keel
once a GRP boat, and had encapsulated lead in an aluminium keel
I must be a terrible sailor as I've hit the bottom at some stage with all the above - and fortunately all survived without damage to the hull
structure or keel / hull
join. The one I worried about the most was the aluminium one - but despite hitting rocks at 7 knots beating up a narrow channel and sticking fast - no leaks
But interestingly when we were having the lead keel cast for the boat we built, the forge wanted to know exactly how hard / soft we wished the keel to be.
They accomodated this by additon or subraction of antimony to the molten lead.
So maybe some of the above stories where lead has taken a bash and simply scored or dented - and others where the load has been tranferred up to the keel / hull join - simply had differing lead / antimony mixes?
I've never seen a production boat spec where this is defined - but just maybe it should be?