It says nothing about how to repeat the cut outs accurately. I would make a router template out of 1/4 inch plastic or aluminum. Build a box that could slide down a plank with peg holes for alignment. Use a single plank to make two rails, rough cut and then route the gaps of two rails together and then rip the plank to form the two rails.

I have been thinking about this a long time.

I have thought about stainless, King starboard and wood alternatives. My rails through-bolt to another set below. The on-deck rails, now 27 years old are very weathered and cracked and need replacing. I can't change the hole spacing because of the through bolts. A stainless fabricator I trust told me that to do all those bolt position would be obscenely expensive and said I could do stainless with a third of the bolt points. That would leave me with a problem fastening the cabin hand rails - I wouldn't like plain old screw heads there.

Eliminating stainless leaves me with a DIY fabrication. I should mention that my replacements will be fourteen loops each and just over 13 feet long. The originals are in two sections and I don't like the position of the gap. Getting the material of that length is a problem I haven't solved. I would need a 5/4 X 7 inches X 14 feet. I'm sure that is why the rails are in two sections now. I suppose I could do a long scarf joint but doing that with one inch teak doesn't sit right with me from a strength perspective.

Any ideas?