I make some out of cedar. They have a 10” radius cut into the board the entire length, the fish will somewhat lay in the “ trough like” radius. I have lines engraved at different measurements and names; fish etc. this one shown was graduation present.
I’ll try to get a picture that shows the radius better. This particular board was basically made for the Roanoke River Rockfish. The keeper fish are from 18”-22”. No fish between 22”-26”. Over 26” falls back into the keeper size.