[abl1111]

You want to look inside the boat, to see where the boat's stringers are - then match that up with, as close as you can, with where the bunks set on the outside of the hull.

For my 23' Tsunami, looking from the aft, it is the first chine from the side of the boat, about 1" in, toward the centerline. I also have centerline rollers for keel support.

Good luck.