One of the changes in surfboard design after boards went from balsa wood to foam was rocker.

The early balsa wood boards were pretty straight from nose to tail. The boards were made by face gluing wood planks together to get a solid piece around 20 inches wide and 9 feet long and thick enough to  cut a surfboard  from. That big block of wood then was cut and shaped into a surfboard not unlike hand shaping an eps blank now days. The difference being eps blanks are profiled and have rocker cut and glued to a stringer.

The wood board was just a big plank. The end result for the most part was a surfboard with a nice outline, as thick as the wood plank would allow with some curve from rail to rail on the bottom, a little curve from rail to rail on the deck, a bottom rocker curve from nose to tail with the decks from nose to tail pretty flat.

The original plugs for surfboard foam molds were similar to the balsa boards of the day. That was what was known, so the early foam boards as far as shape were quite similar to the balsa boards.

The bottom rockers were ok but because the decks were flat the rail line from nose to tail was pretty straight. That long straight rail line began to change from the early sixties, because the foam blanks could be made with nose to tail deck curve and when a wood stringer was glued into the blank it helped keep that curve in place. As well you could cut the stringer to any number of bottom and deck curves for custom rockers.

With bottom and deck curves better surfboards became more maneuverable, combined with the foam cores which made boards lighter performance surfing was getting it's start.

D.R.

It may be a little hard to see but in the above picture I've pulled a string from nose to tail across an early sixties surfboard. I can barely get the fingers of my left hand between the string and deck... pretty flat deck curve.

This second picture is from a mid sixties type board. The space between the string and deck of this boards is double the space of the early sixties board.

Again it's a little hard to see but the rail line curve is quite different between the two.