Shims
The shims will support the 1st planks on each side.The shims will be epoxied to the ribs. All of them will have a gap of 1 inch to the keelson in order for the water to flow to the back.
The angles are adjusted from rib to rib. Most of them are between 8 and 12 degrees.
I used the miter saw to cut the shims. With a little jig I was holding down the narrow pieces. I still have all my fingers!