You don't need a stringer in one of these boards except in extreme circumstances like a big wave gun or tow board (in which the stringer needed would be extremely thin). Without the need for a stringer, boards made with Varial Foam have a more consistent flex throughout.

Why do you need a stringer in a surfboard?

Stringer Notes - Stringers are used to stiffen a surfboard blank for shaping purposes. Without a piece of wood glued into the centre of a blank the foam on its own would be too floppy, particularly in small, thin blanks. Stringers are used for decoration.

Do all surfboards have a stringer?

A classic shortboard usually features a 3/16'' (4.7 mm) wide stringer; big wave guns and longboards have 3/8'' (9.5 mm) stringers. However, epoxy-based boards don't usually incorporate any stringer. There are also parabolic stringers. They add an arc along the rails of the board for extra memory flex.