I'm almost done building the same exact boat. I laminated the coaming from 1/8 inch thick fir strips, but am going to use 1/4 inch ply for the lip.

I was of the understanding that traditionally, the coaming was only attached to the skin, not to the frame. I have already skinned the boat in polyester, and painted it so that the thread won't pull when I stitch it to the inside of the coaming. I will be stitching the coaming on shortly.

Am I doing this right? I thought some flexibility in the coaming (ie stitching it to the skin only) was a good thing, especially for rolling? haha after all this work is my 18x30 keyhole coaming going to rip out in use?