It is hard to beleive that shuch a large void happened in the bottom of the mould, in such a critical place and would go unnoticed in the factory or take 15years to reveal itself. I have never seen a void in a straight line either, other than damage when compressed around a frame or bulkhead . Is the crack /void under the inner wall of the grid liner?
The first pic with the keel on, it appears there is a considerable gap to the hull at the forward part of the keel, rings an alarm, has the boat had a significant grounding? I have repaired and assisted with few boats repairs over the years, but I am not a boatbuilder.
Is the internal grid well bonded/ undamaged, particularly look aft of the keel. I have a 2009 45p and my grid is well glassed to the hull around the keel area, but glued elsewhere less critical.
I have never seen or heard of a bolt on keel that didnt have straight bolts from new, this would be incredibly bad engineering practice, as you would significantly reduce their strenght of the bolts. Were the nuts and backing plates flush with the floor of the hull?
Possibly Dufour had a seriously rough bugger on the job and didnt check the drilling template with the keel for an exact match…. any hammer marks on the bolts or elongation of the keel bolt holes?
Or could the keel have been replaced with one that didn’t match the hull?
Has your surveyor carried out a hammer test on the rest of the hull… looking for other voids?
I am not suprised your surveyor has had no luck talking to anyone at Dufour, I have tried to source basic info, but no one replies, Dufour could be helpful and add to there website a simple statment, ” Past clients go F… yourselfves”, would have saved me time trying.
All the best