Thanks all for your replies. Yes it has a keel. To answer Toddster's question about method of repair, basically the yard told me they would grind down the hull from outside (a lot of grinding!) over and beyond the affected area, feathered in, then re-glass the whole thing. They told me they do this routinely and that it would be stronger than new. I was roughly quoted $3000 to $4000 for the repair. I am hoping my insurance can cover at least part of it, they are sending a surveyor. I was wondering if anyone ever went through the same kind of repair with their E30 and if it really held as well as I was told it would. ...The sad thing is that it was only my 3rd outing; I am starting to regret selling my 1973 E27, which was in fantastic shape and solid as a rock.
When I first saw your post with the pictures, my guess was along the lines of what Loren suggested: that this model had the hull laid up in two halves and then was joined together--the failure here being at that joint.
Regardless, I'd suggest that you find the most knowledgeable surveyor you can have have him look at it. Perhaps the one the insurance company is sending will fit the bill, but check out that person's qualifications carefully. Simply being a "surveyor" doesn't mean they really know a whole lot.
The other thing is that I'd want to attack that repair from both sides, not just the outside. It's obvious why the yard would want to do it entirely from the outside, because internal access may be limited. Repairing it from the outside makes the work far easier for them. But this is a very, very important structural repair and getting at it from both sides can only make it stronger.
As for the price: $4K strikes me as pretty high for a repair done solely from the outside, where access is simple. But then, I am often surprised by what things cost. Get a few more bids on it for a point a comparison. Also, find out specifically what materials they are proposing to use for this. Epoxy? (Probably the best bet.) Vinylester resin? Polyester resin? (Not so hot for secondary bonds.) Again, a *good* surveyor will help you navigate all of this.
Blessings to you and I hope you are able to get a good resolution to this.