I'm building a Rapid Roberts . The question is the size, the plan calls for 5/8 x 1-1/8 this seems small to me . I guess i need reassurance this will work.
That would be exactly right. Anything larger than 5x8 is too hard to bend to shape. Remember the chine log (or inside chine) will be supported by the side and then by the outside chine batten. After the sandwich of inside chine (5/8) side panel (1/4) and chine batten (1/2) you have 1 3/8 thickness of laminated wood at the chine. If you put a stainless steel trim on the outside of your chine batten then it will take a life threatening rock smack to damage the chine area.
I built my first boat with 3/4" W.Oak. broke two getting them in.
managed to do it, but it was NOT fun.
Two more boats, but both are 5/8." as a matter of fact, all the trim, rails, chines, chine batten are 5/8" on my boats. Simplifies the planing and planning process.