For the circles:
This is how I do the markup for deck or hull planking. I print piece of paper that is divided to equal segments. The quantity of the segments is equal to the quantity of the planks on the deck per side. Using this piece of paper I am able to divide the deck width (from centerline to waterway piece) at any place by the same number of planks, and they all will have equal width regardless of the local deck width. Like this:
View attachment 106296
When the deck width becomes smaller you just tilt more the piece of paper, it still gives you equal division.
Now, I put the marks not with a pencil, but with a knife. It's much more precise. And finally, to highlite the knife marks I just circle them with pencil - to be able to quickly find them and not loose