Hi Conrad,
The NACA 63 series foils have the hollow/concave surfaces approaching the trailing edge. When you look at the Cd vs Cl curve, drag coefficient vs lift coefficient, you also see that there is a significant drag coefficient reduction in this curve, called the drag bucket, at low angles of attack relative to other foil shapes.
It doesn't cost any more to make a mold that produces parts of lower drag characteristics than it does to make a mold that produces parts of higher drag characteristics. Have you ever seen a production daggerboard or rudder foil shape with the hollow surfaces approaching the trailing edge on any production boat, Hobie, Prindle, NACRA, etc, except the Marstrom Tornado?
Bill
PS If you are really interested in NACA foil sections, get the book, THEORY OF WING SECTIONS" by Abbott and Von Doernhoff.