Yep, this is one lucky boat. Out of intensive care and now onto full recovery....
So I can say from first-hand experience, this was caused by a hard-grounding. I ran aground hard in the bight at Cape Lookout last Fall (the channels shift quite a bit, and create shelves of sand that are practically vertical. Yep, that's what I ran into at 6 knots). Now, I have an almost identical crack (compared to photos posted above) in the roving atop my keel that goes about two feet, from the middle access hole in the bilge, up to the compression post bulkhead. I discovered it today, while the boat was on the hard, and just before I had to drive 3hrs back home. Sorry I don't have any photos, I'll try to take one next week when I'm back down on the boat.
I didn't realize what damage I had done when I ran aground this past October. I looked in the bilge immediately afterwards for water, and it was dry. I looked in the aft bilge access hole and so didn't see the crack (it started under the middle access hole). The boat went on a two more trips afterwards in 2013, and wintered on her mooring. She is hauled out right now for a new bottom coat, and one of my tasks in the haul out was to study the exterior fiberglass for any signs of cracks (I even pinged around the keel and surrounding underbody for delimitation. All felt solid).
The roving that is cracked, directly over the keel, on my boat is very thin - maybe two layers of roving at the most, and no more than 1/16-inch thick. So what I suspect happened was the hull flexed when running aground pushing the keel up ever so much, and that area, being the thinnest and experiencing a significant tensile force as the keel was pushed up, cracked and parted. If the glass there is meant to be structural, I have to think it would have been thicker. I think it was merely to cover up the keel resin, scrap, what have you. I will have the yard owner (Alan, for those of you familiar with Oriental, NC - he knows his s..t!) take a look. I suspect it will be fine to relaunch her and sail this season.
But I do want to repair her, and when I do, I will come back to this thread for valuable insight. I will gut the floor along with the compression post stringer (if you can call it that), and glass in structural stringers (akin to structural grid employed in later Ericson's) as a floor base and then lay down something nice - teak & holly, or bamboo, etc.
Let us know when you get ready to do your TFG project. I can show pictures from my project that you may find interesting.
Very nice work. Thanks for sharing. This gives me inspiration for my project. I am excited to replace the floor - I never liked the fiberglass cabin sole, and rugs were always awkward. I can envision a grid like that, to which a decorative floor attaches - perhaps a marine ply with teak or bamboo laminated on the surface. Lets face it - the floor is only something like 3' x 4'. We're not talking major surgery here, only minor....
Will post photos once I've committed to something. Thanks again, PDX!