Today I powerwashed the hull below the waterline and found a crevice on the lower half of the keel trunk that has been hidden by the black bottom paint that was put on by the previous owner. When I push on the area adjacent to the crevice water comes out. I presume it was forced in by the powerwasher. So I've got a hole there. I also tapped the trunk all around with the handle of a screwdriver and found there are several spots that sound hollow. There is some outward bulging in some of the hollow sounding areas, but not all. So I don't know if I'm dealing with osmotic blistering or areas that the concrete ballast inside has pulled away from the fiberglass skin. So my question is, is the concrete attachment to the skin necessary for the strength of the keel trunk, or is the trunk itself strong enough to support the weight of the boat?
Wanted to follow up my post with a couple of things I've learned in case anyone has a similar problem/question. I called Hutchins this morning and asked my question. The answer is that concrete doesn't stick to fiberglass and so the keel trunk sounding hollow is not uncommom. When the concrete is first poured there is some attachment, but as it ages and cures it shrinks some and pulls away. There is some strength derived from having a plug of concrete behind the fiberglass, but the majority of strength is in the laminate.