Yep, a location on the hull would be nice to know. Judging from the scratches it may be in the rear of the hull. Something structural has failed to cause enough flex for metal fatigue. If it is in the rear then it could be the transom brace or the transom itself is rotted causing flex/deflection. That'[s usually a pretty strong area of the hull.
You need to find and repair the structural component first, then you can repair the crack with HTS 2000 very easily; be sure to drill the cracks to keep them from running.