These frame grabs are from a humorous skit featuring Hevs McClelland, shot by Bruce Brown in the mid-60's. Without realizing it, they provided a nice perspective of the complexity of the "plank" surfboard.
The entire bottom is a compound curve displacement hull. Every square inch is engineered.
It appears to be around 3 inches thick, which means there was plenty of room for rocker curve to be shaped into it.
The shots also show a flattish belly under the nose, V in the tail, a nice rocker break/knuckle in the front 1/3, and a tapered rail in the tail. All the convex 'drag and suction' are in exactly the right place for a finless board that weighed over 100 pounds.
Bottom line? The pre-1945 shapers knew what they were doing!