What is this upside down roof peak or boat hull? Here's another mystery piece from my collection. I'm not 100% sure it's genuine LEGO, but I would love to know whether it is, and if so, what part. It attaches to the bottom of a 2x8 brick securely. No markings to identify branding or part numbers, but other legos it came with were from 1970s era.

It kind of looks like it ought to be a curved roof peak, except it's upside down. Maybe the bottom of a boat hull? But what about the notched slots on the bottom? 

* there is a small crack in the narrow end of the brick. The left side is what both sides should look like.
It looks to me like this is a Weighted Keel 2 x 8 x 4 (x149). I don't personally have this part, but it looks like your part is this part broken in two:



These were mounted under the floating boats of the late 70s and early 80s.