Couple more thoughts, on my '62 Columbia
is structurally there, though it still looks a little rough. Still have finish work to do; fill in the previous arch cut-out and a cosmetic hardwood arch covering the bolts, some paint
... The arch is 6 inches wide, made of layers of laminated plywood
and has 3, 1/4" thick arches of aluminum
embedded. So far, so good and I have pushed her pretty hard since putting it in. And... I can confirm, you can row an 8000# boat, but not very fast. On the positive side though, getting in and out of a slip is very easy!